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Type Conversion in Go

Type Conversion in Go
Hostman Team
Technical writer
Go
10.12.2024
Reading time: 10 min

Go is a statically typed programming language, meaning that data types are tied to variables. If you declare a variable as int to store numerical values, you cannot store a string in it. This rule works in the reverse direction as well.

Static typing protects developers from errors where the program expects one data type and gets another. However, this strict binding can be limiting when performing certain operations. Go provides type conversion (or type casting) to overcome this limitation. This formal process allows developers to convert integer values to floating-point numbers, strings to numbers, and vice versa. This article will help you understand how to perform such conversions.

Data Types in Go

The basic types in Go are as follows:

  • bool — Boolean values: true or false
  • string — Strings
  • int, int8, int16, int32, int64 — Signed integer types
  • uint, uint8, uint16, uint32, uint64, uintptr — Unsigned integer types
  • byte — Alias for uint8
  • rune — Alias for int32
  • float32, float64 — Floating-point numbers
  • complex64, complex128 — Complex numbers

The types int, uint, and uintptr have a width of 32 bits in 32-bit systems and 64 bits in 64-bit systems. When you need an integer value, you should use int unless you have a specific reason for using a sized or unsigned integer type.

Go does not have a char data type. The language uses byte and rune to represent character values. byte represents ASCII characters, while rune represents a broader set of Unicode characters encoded in UTF-8.

To define characters in Go, you enclose them in single quotes like this: 'a'. The default type for character values is rune. If you do not explicitly declare the type when assigning a character value, Go will infer the type as rune:

var firstLetter = 'A' // Type inferred as `rune`

You can explicitly declare a byte variable like this:

var lastLetter byte = 'Z'

Both byte and rune are integer types. For example, a byte with the value 'a' is converted to the integer 97. Similarly, a rune with the Unicode value '♥' is converted to the corresponding Unicode code point U+2665, where U+ indicates Unicode, and the numbers are in hexadecimal, which is essentially an integer.

Here's an example:

package main
import "fmt"
func main() {
    var myByte byte = 'a'
    var myRune rune = '♥'
    fmt.Printf("%c = %d and %c = %U\n", myByte, myByte, myRune, myRune)
}

Output:

a = 97 and ♥ = U+2665

When you need to convert from int to string or vice versa, you essentially take the type initially assigned to a variable and convert it to another type. As mentioned earlier, Go strictly formalizes these actions. The examples in this article will help you understand the basics of such conversions.

Number Conversion in Go

Converting numeric types can be useful when solving various tasks. For example, we decided to add a calculator to the website. It should perform only one operation: division. The main requirement is that the result be accurate down to the last digit.

However, when dividing two integer variables, the result may be inaccurate. For example:

package main
import "fmt"

func main() {
    var first int = 15
    var second int = 6
    var result = first / second
    fmt.Println(result)
}

Output:

2

After executing this code, you get 2. The program outputs the nearest integer quotient, but this is far from the precise division you need. Such a calculator is not useful.

To improve the accuracy, you need to cast both variables to float. Here's how you can do it:

package main
import "fmt"

func main() {
    var first int = 15    
    var second int = 6    
    var result = float64(first) / float64(second)    
    fmt.Println(result)
}

Output:

2.5

Now the output will be precise — 2.5. It was quite easy to achieve by simply wrapping the variables with the float64() or float32() conversion functions. Now the calculator works as expected. Product metrics are not a concern, as the feature is technically implemented correctly.

You can also divide numbers without explicitly converting them to float. When you use floating-point numbers, other types are automatically cast to float. Try this code:

package main
import "fmt"

func main() {
    a := 5.0 / 2
    fmt.Println(a)
}

Output:

2.5

Even though you didn’t explicitly use the float64() or float32() wrapper in the code, Go's compiler automatically recognizes that 5.0 is a floating-point number and performs the division with the floating-point precision. The result is displayed as a floating-point number.

In the first example with division, you explicitly cast the integers to float using the float64() function. Here’s another example of converting from int64 to float64:

package main
import "fmt"

func main() {
    var x int64 = 57
    var y float64 = float64(x)
    fmt.Printf("%.2f\n", y)    
}

Output:

57.00

The two zeros after the decimal point appear because we added the %.2f\n format specifier. Instead of 2, you could specify any other number, depending on how many decimal places you want to display.

You can also convert from float to int. Here's an example:

package main
import "fmt"

func main() {
    var f float64 = 409.8
    var i int = int(f)
    fmt.Printf("f = %.3f\n", f)
    fmt.Printf("i = %d\n", i)
}

Output:

f = 409.800
i = 409

In this example, the program prints f = 409.800 with three decimal places. In the second print statement, the float is first converted to int, and the decimal part is discarded. Note that Go does not perform rounding, so the result is 409 without any rounding to the nearest integer.

Strings Conversion in Go

In Golang, we can convert a number to a string using the method strconv.Itoa. This method is part of the strconv package in the language's standard library.

Run this code:

package main
import (
    "fmt"
    "strconv"
)

func main() {
    a := strconv.Itoa(12)
    fmt.Printf("%q\n", a)
}

The result should be the string "12". The quotes in the output indicate that this is no longer a number.

In practice, such string-to-number and number-to-string conversions are often used to display useful information to users. For example, if you're building an online store, you can host it at Hostman, implement the core business logic, and fill it with products.

After some time, the product manager suggests improving the user profile. The user should see the amount they have spent and how much more they need to spend to reach the next level. To do this, you need to display a message in the user profile that consists of a simple text and a set of digits.

Try running this code:

package main
import (
    "fmt"
)

func main() {
    user := "Alex"
    sum := 50
    fmt.Println("Congratulations, " + user + "! You have already spent " + lines + " dollars.")
}

The result will be an error message. You cannot concatenate a string and a number. The solution to this problem is to convert the data in Go.

Let's fix the code by converting the variable lines to a string:

package main
import (
    "fmt"
    "strconv"
)

func main() {
    user := "Alex"
    sum := 50
    fmt.Println("Congratulations, " + user + "! You have already spent " + strconv.Itoa(sum) + " dollars.")
}

Now, there will be no error, and the output will display the correct message with the proper set of digits. Of course, this is a simplified example. In real projects, the logic is much more complex and challenging. However, knowing the basic operations helps avoid a large number of errors. This is especially important when working with complex systems.

Let's go back to our example. The product manager comes again and says that customers want to see the exact total amount of their purchases in their profile, down to the pennies. An integer value won't work here. As you already understood from the examples above, all digits after the decimal point are simply discarded. To make sure the total purchase amount in the user profile is displayed correctly, we will convert not an int, but a float to a string.

For this task, there is a method fmt.Sprint, which is part of the fmt package.

package main
import (
    "fmt"
)
func main() {
    fmt.Println(fmt.Sprint(421.034))
    f := 5524.53
    fmt.Println(fmt.Sprint(f))
}

To verify that the conversion was successful, concatenate the total with the string. For example:

package main
import (
    "fmt"
)
func main() {
    f := 5524.53
    fmt.Println("Alex spent " + fmt.Sprint(f) + " dollars.")
}

There is no error now, and the information message correctly displays the floating-point number. Customers can see how much money they've spent in your store, with all expenses accounted for down to the penny.

A common reverse task is to convert a string into numbers. For example, you have a form where the user enters their age or any other numeric values. The entered data is saved in the string format. Let's try working with this data— for instance, performing a subtraction:

package main
import (
    "fmt"
)
func main() {
    lines_yesterday := "50"
    lines_today := "108"
    lines_more := lines_today - lines_yesterday
    fmt.Println(lines_more)
}

The result of running this code will be an error message, as subtraction cannot be applied to string values. To perform mathematical operations on data stored as strings, you need to convert them to int or float.

The choice of method depends on the type you will convert the string to. If you are working with integers, use the strconv.Atoi method. For floating-point numbers, use the strconv.ParseFloat method.

package main
import (
    "fmt"
    "log"
    "strconv"
)
func main() {
    lines_yesterday := "50"
    lines_today := "108"
    yesterday, err := strconv.Atoi(lines_yesterday)
    if err != nil {
        log.Fatal(err)    }
    today, err := strconv.Atoi(lines_today)
    if err != nil {
        log.Fatal(err)
    }
    lines_more := today - yesterday
    fmt.Println(lines_more)
}

In this example, you use the if operator to check whether the conversion was successful. If an error occurs, the program will terminate, and the error information will be saved in the log. If the conversion is successful, the output will give you the correct result: 108 - 50 = 58.

If you try to convert a string that does not contain a numerical value in the same way, you will receive an error message:

strconv.Atoi: parsing "not a number": invalid syntax

Try running this code:

package main
import (
    "fmt"
    "strconv"
)
func main() {
    a := "not a number"
    b, err := strconv.Atoi(a)
    fmt.Println(b)
    fmt.Println(err)
}

The code from the example above will fail because you are trying to convert a string whose value is not a number into a numeric type.

Strings can also be converted to byte slices and back using the []byte() and string() constructs. 

package main
import (
    "fmt"
)
func main() {
    a := "hostman"
    b := []byte(a)
    c := string(b)
    fmt.Println(a)
    fmt.Println(b)
    fmt.Println(c)
}

In this function, you save the string to variable a, then convert the same string into a byte slice and save it to variable b, then turn the byte slice into a string and save the result to variable c. The output will be like this:

hostman
[104 111 115 116 109 97 110]
hostman

This simple example shows that you can easily convert strings to byte slices and back.

Conclusion

In this article, we only covered the basics. We looked at the available data types and how to perform type conversion in Go.

If you want to learn more, explore the language documentation or at least the "A Tour of Go" tutorial — it's an interactive introduction to Go divided into three sections. The first section covers basic syntax and data structures, the second discusses methods and interfaces, and the third introduces Go's concurrency primitives. Each section concludes with several exercises so you can practice what you've learned. 

In addition,  you can deploy Go applications (such as Beego and Gin) on our app platform.

Go
10.12.2024
Reading time: 10 min

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Let's create a dictionary named record1, containing three keys: record1 = { "name": "Alex", "age": 25, "location": "London" } To insert the dictionary data, use the insert_one method in MongoDB. insertrecord = collection1.insert_one(record1) import pymongo connect_to_mongo = pymongo.MongoClient("mongodb://91.206.179.29:27017/") db1 = connect_to_mongo["newdb"] collection1 = db1["userdata"] record1 = { "name": "Alex", "age": 25, "location": "London" } insertrecord = collection1.insert_one(record1) print(insertrecord) Run the script: python3 connect_mongodb.py ClickHouse and Python ClickHouse is a columnar NoSQL database where data is stored in columns rather than rows. It is widely used for handling analytical queries. Install the ClickHouse driver for Python. There is a dedicated plugin for ClickHouse called clickhouse-driver. Install the driver using the pip package manager: pip install clickhouse-driver Connect to ClickHouse. To initialize a connection with ClickHouse, you need to import the Client class from the clickhouse_driver library. To execute SQL queries, use the client.execute function. You also need to specify the engine. For more details on supported engines in ClickHouse, you can refer to the official documentation. We'll use the default engine, MergeTree. Next, create a new table called users and insert two columns with data. To list the data to be added to the table, use the tuple data type. After executing the necessary queries, make sure to close the connection to the database using the client.disconnect() method. The final code will look like this: from clickhouse_driver import Client client = Client(host=91.206.179.128', user='root', password='P@$$w0rd123', port=9000) client.execute(''' CREATE TABLE IF NOT EXISTS Users ( id UInt32, name String, ) ENGINE = MergeTree() ORDER BY id ''') data = [ (1, 'Alice'), (2, 'Mary') ] client.execute('INSERT INTO Users (id, name) VALUES', data) result = client.execute('SELECT * FROM Users') for row in result: print(row) client.disconnect() Database Connection in Go Go is one of the youngest programming languages, developed in 2009 by Google.  It is widely used in developing microservice architectures and network utilities. For example, services like Docker and Kubernetes are written in Go. Go supports integrating all popular databases, including PostgreSQL, Redis, MongoDB, MySQL, ClickHouse, etc. MySQL and Go For working with the MySQL databases in Go, use the go-sql-driver/mysql driver. Create a new directory for storing project files and navigate into it: mkdir mysql-connect && cd mysql-connect Create a go.mod file to store the dependencies: go mod init golang-connect-mysql Download the MySQL driver using the go get command: go get -u github.com/go-sql-driver/mysql Create a new file named main.go. Specify the database connection details in the dsn variable: package main import ( "database/sql" "fmt" "log" _ "github.com/go-sql-driver/mysql" ) func main() { dsn := "root:password@tcp(localhost:3306)/testdb" db, err := sql.Open("mysql", dsn) if err != nil { log.Fatal(err) } defer db.Close() if err := db.Ping(); err != nil { log.Fatal(err) } fmt.Println("Successfully connected to the database!") query := "INSERT INTO users (name, age) VALUES (?, ?)" result, err := db.Exec(query, "Alex", 25) if err != nil { log.Fatal(err) } lastInsertID, err := result.LastInsertId() if err != nil { log.Fatal(err) } fmt.Printf("Inserted data with ID: %d\n", lastInsertID) } PostgreSQL and Go To connect to PostgreSQL, use the pq driver. Before installing the driver, let's prepare our environment. Create a new directory for storing the project files and navigate into it: mkdir postgres-connect && cd postgres-connect Since we will be working with dependencies, we need to create a go.mod file to store them: go mod init golang-connect-postgres Download the pq driver using the go get command: go get github.com/lib/pq Create a new file named main.go. In addition to importing the pq library, it is necessary to add the database/sql library as Go does not come with official database drivers by default. The database/sql library consists of general, independent interfaces for working with databases. It is also important to note the underscore (empty identifier) when importing the pq module: _ "github.com/lib/pq" The empty identifier is used to avoid the "unused import" error, as in this case, we only need the driver to be registered in database/sql. The fmt package is required to output data to the standard output stream, for example, to the console. To open a connection to the database, the sql.Open function is used, which takes the connection string (connStr) and the driver name (postgres). The connection string specifies the username, database name, password, and host address: package main import ( "database/sql" "fmt" "log" _ "github.com/lib/pq" ) func main() { connStr := "user=golang dbname=db_for_golang password=Golanguserfordb0206$ host=47.45.249.146 sslmode=disable" db, err := sql.Open("postgres", connStr) if err != nil { log.Fatal(err) } defer db.Close() err = db.Ping() if err != nil { log.Fatal(err) } fmt.Println("Successfully connected to PostgreSQL!") } Compile and run: go run main.go If everything works correctly, the terminal will display the message Successfully connected to PostgreSQL! Now, let's look at an example of how to insert data into a table.  First, we need to create a table in the database. When using Hostman cloud databases, you can copy the PostgreSQL connection string displayed in the "Connections" section of the Hostman web interface. Make sure that the postgresql-client utility is installed on your device beforehand. Enter the psql shell and connect to the previously created database: \c db_for_golang Create a table named Cities with three fields — city_id, city_name, and city_population: CREATE TABLE Cities ( city_id INT PRIMARY KEY, city_name VARCHAR(45) NOT NULL, city_population INT NOT NULL); Grant full privileges to the created table for the user: GRANT ALL PRIVILEGES ON TABLE cities TO golang; The function db.Prepare is used to prepare data. It specifies the query for insertion in advance. To insert data, use the function stmt.Exec. In Go, it's common to use plain SQL without using the ORM (Object-Relational Mapping) approach. stmt, err := db.Prepare("INSERT INTO Cities(city_id, city_name, city_population) VALUES($1, $2, $3)") if err != nil { log.Fatal(err) } defer stmt.Close() _, err = stmt.Exec(1, "Toronto", 279435) if err != nil { log.Fatal(err) } fmt.Println("Data inserted successfully!") } If all works correctly, you will see: Data inserted successfully! Redis and Go To connect to Redis, you need to use the go-redis driver. Сreate a new directory: mkdir connect-to-redis && cd connect-to-redis Prepare the dependency file: go mod init golang-connect-redis And optimize them: go mod tidy Download the go-redis module: go get github.com/go-redis/redis/v8 To connect to Redis, use the redis.Options function to specify the address and port of the Redis server. Since Redis does not use authentication by default, you can leave the Password field empty and use the default database (database 0): package main import ( "context" "fmt" "log" "github.com/go-redis/redis/v8" ) func main() { rdb := redis.NewClient(&redis.Options{ Addr: "91.206.179.128:6379", Password: "", DB: 0, }) ctx := context.Background() _, err := rdb.Ping(ctx).Result() if err != nil { log.Fatalf("Couldn't connect to Redis: %v", err) } fmt.Println("Successfully connected to Redis!") } You should see the message «Successfully connected to Redis!» MongoDB and Go To work with MongoDB, we'll use the mongo driver. Create a new directory to store the project structure: mkdir connect-to-mongodb && cd connect-to-mongodb Initialize the dependency file: go mod init golang-connect-mongodb Download the mongo library: go get go.mongodb.org/mongo-driver/mongo Connect to MongoDB using the options.Client().ApplyURI method. It takes a connection string such as mongodb://91.206.179.29:27017, where 91.206.179.29 is the MongoDB server address and 27017 is the port for connecting to MongoDB. The options.Client().ApplyURI string is used only for specifying connection data. To check the connection status, you can use another function, client.Ping, which shows the success or failure of the connection: package main import ( "context" "fmt" "log" "time" "go.mongodb.org/mongo-driver/mongo" "go.mongodb.org/mongo-driver/mongo/options" ) func main() { clientOptions := options.Client().ApplyURI("mongodb://91.206.179.29:27017") client, err := mongo.Connect(context.TODO(), clientOptions) if err != nil { log.Fatalf("Couldn't connect to MongoDB server: %v", err) } fmt.Println("successfully connected to MongoDB!") ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second) defer cancel() err = client.Ping(ctx, nil) if err != nil { log.Fatalf("Could not ping MongoDB server: %v", err) } fmt.Println("Ping MongoDB server successfully!") } You should see the message: successfully connected to MongoDB!Ping MongoDB server successfully MongoDB uses collections to store data. You can create collections using the .Collection function.  Below, we will create a database called first-database and a collection called first-collection. The collection will have a new document, containing three keys: user-name, user-age, and user-email. collection := client.Database("first-database").Collection("first-collection") document := map[string]interface{}{ "user-name": "Alice", "user-age": 25, "user-email": "alice@corporate.com", } insertResult, err := collection.InsertOne(ctx, document) if err != nil { log.Fatalf("Couldn't insert new document: %v", err) } fmt.Printf("Inserted new document with ID: %v\n", insertResult.InsertedID) if err := client.Disconnect(ctx); err != nil { log.Fatalf("Could not disconnect from MongoDB: %v", err) } fmt.Println("Disconnected from MongoDB!") } If successful, you will see the Inserted new document message with the document ID.  ClickHouse and Go To work with ClickHouse, use the clickhouse-go driver. Create a new directory to store the project files and navigate to it: clickhouse-connect && cd clickhouse-connect Create a go.mod file to store the dependencies: go mod init golang-connect-clickhouse Download the Clickhouse driver using the command: go get github.com/ClickHouse/clickhouse-go/v2 Create a new file named main.go, where you will specify the connection data to ClickHouse. package main import ( "database/sql" "log" "github.com/ClickHouse/clickhouse-go/v2" ) func main() { dsn := "tcp://localhost:9000?username=user1&password=PasswordForuser175465&database=new_db" db, err := sql.Open("clickhouse", dsn) if err != nil { log.Fatal(err) } defer db.Close() if err := db.Ping(); err != nil { log.Fatal(err) } log.Println("Connected to ClickHouse!") } Database Connection in JavaScript In JavaScript, all connections to external services are made using the Node.js platform. Make sure that you have Node.js and the npm package manager installed on your device. MySQL and JavaScript To work with MySQL, use the mysql2 driver. Create a directory where we will store the project files: mkdir js-mysql-connect && cd js-mysql-connect Initialize the project: npm init -y Install the mysql2 library: npm install mysql2 Use the following code to connect to MySQL: const mysql = require('mysql2'); const connection_to_mysql = mysql.createConnection({ host: 'localhost', user: 'root', password: 'PasswordForRoot74463', database: db1, }); connection_to_mysql.connect((err) => { if (err) { console.error('Error connecting to MySQL:', err.message); return; } console.log('Successfully connected to MySQL Server!'); connection_to_mysql.end((endErr) => { if (endErr) { console.error('Error closing the connection_to_mysql:', endErr.message); } else { console.log('Connection closed.'); } }); }); PostgreSQL and JavaScript Connecting to PostgreSQL is done using the pg library. Create a directory where we will store the project files: mkdir js-postgres-connect && cd js-postgres-connect Initialize the project: npm init -y Install the pg library: npm install pg To connect to PostgreSQL, first import the pg library. Then, create a constant where you specify variables for the database address, username, password, database name, and port. Use the new pg.Client class to pass the connection data. We will create a table called cities and add two records into it. To do this, we will use the queryDatabase function, which contains the SQL queries. const pg = require('pg'); const config = { postgresql_server_host: '91.206.179.29', postgresql_user: 'gen_user', postgresql_user_password: 'PasswordForGenUser56467$', postgresql_database_name: 'default_db', postgresql_database_port: 5432, }; const client = new pg.Client(config); client.connect(err => { if (err) throw err; else { queryDatabase(); } }); function queryDatabase() { const query = ` DROP TABLE IF EXISTS cities; CREATE TABLE cities (id serial PRIMARY KEY, name VARCHAR(80), population INTEGER); INSERT INTO cities (name, population) VALUES ('Berlin', 3645000); INSERT INTO cities (name, population) VALUES ('Paris', 2161000); `; client .query(query) .then(() => { console.log('Table created successfully!'); client.end(console.log('Closed client connection')); }) .catch(err => console.log(err)) .then(() => { console.log('Finished execution, exiting now'); process.exit(); }); } Use this command to run the code: node connect-to-postgres.js Redis and JavaScript To work with Redis, use the ioredis library. Create a directory to store the project files: mkdir js-redis-connect && cd js-redis-connect Initialize the project: npm init -y Install the ioredis library: npm install ioredis To connect to Redis, import the ioredis library. Then create a constant named redis and specify the Redis server address. Inserting data, i.e., creating key-value objects, is done using an asynchronous function named setData, which takes two values — key and value, corresponding to the data format of the Redis system. const Redis = require('ioredis'); const redis = new Redis({ host: '91.206.179.29', port: 6379, password: 'UY+p8e?Kxmqqfa', }); async function setData(key, value) { try { await redis.set(key, value); console.log('Data successfully set'); } catch (error) { console.error('Error setting data:', error); } } async function getData(key) { try { const value = await redis.get(key); console.log('Data retrieved'); return value; } catch (error) { console.error('Error getting data:', error); } } (async () => { await redis.select(1); await setData('user', 'alex'); await getData('user'); redis.disconnect(); })(); Run: node connect-to-redis.js MongoDB and JavaScript To work with MongoDB, use the mongodb driver. Create a directory for storing the project files: mkdir js-mongodb-connect && cd js-mongodb-connect Initialize the project: npm init -y Install the mongodb library: npm install mongodb To connect to MongoDB, import the mongodb library. Specify the database address in the constant uri and pass the address into the MongoClient class. const { MongoClient } = require('mongodb'); const uri = "mongodb://91.206.179.29:27017"; const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true }); async function connectToDatabase() { try { await client.connect(); console.log("Successfully connected to MongoDB!"); const database = client.db("myDatabase"); const collection = database.collection("myCollection"); const documents = await collection.find({}).toArray(); console.log("Documents found:", documents); } catch (error) { console.error("Error connecting to MongoDB:", error); } finally { await client.close(); console.log("Connection closed."); } } connectToDatabase(); ClickHouse and JavaScript To work with ClickHouse, use the clickhouse/client driver. Create a directory where we will store the project files: mkdir js-clickhouse-connect && cd js-clickhouse-connect Initialize the project: npm init -y Install the @clickhouse/client library: npm install @clickhouse/client To connect to ClickHouse, use the code below where we set the connection details and execute a simple SQL query that will return the first 10 records from the system table named system.tables: const { ClickHouse } = require('@clickhouse/client'); const client = new ClickHouse({ host: 'http://localhost:8123', username: 'default', password: 'PasswordforDefaultUser45435', database: 'default', }); async function connectAndQuery() { try { console.log('Successfully connected to ClickHouse Server!'); const rows = await client.query({ query: 'SELECT * FROM system.tables LIMIT 10', format: 'JSON', }).then((result) => result.json()); console.log('Query results:', rows); } catch (error) { console.error('Error Successfully connected to ClickHouse Server! or running the query:', error); } finally { console.log('Done.'); } } connectAndQuery(); Conclusion In today's article, we thoroughly explored how to connect to PostgreSQL, Redis, MongoDB, MySQL, and ClickHouse databases using Python, Go, and JavaScript. These languages can be used to create both web applications and microservices that utilize databases in their operation.
18 February 2025 · 23 min to read
Go

Working with Date and Time in Go Using the time Package

Go (Golang), like many other programming languages, has a built-in time package that provides special types and methods for working with dates and times. You can find comprehensive information about the time package in the official documentation. This guide will cover the basic aspects of working with time in Go.  All the examples shown were run on a cloud server provided by Hostman, using the Ubuntu 22.04 operating system and Go version 1.21.3. It is assumed that you are already familiar with the basics of Go and know how to run scripts using the appropriate interpreter command: go run script.go Parsing, Formatting, and Creating Dates Before getting started with time manipulation, it's important to understand a key feature of time formatting in Go. In most programming languages, date and time formats are specified using special symbols, which are replaced by values representing day, month, year, hour, minute, and second. However, Go approaches this differently. Instead of special symbols, it uses default date and time values represented by an increasing sequence of numbers: 01-02-03-04-05-06 This sequence of numbers represents: 1st month of the year (January) 2nd day of the month 3rd hour in 12-hour format (p.m.) 4th minute in 12-hour format (p.m.) 5th second in 12-hour format (p.m.) 6th year of the 21st century Thus, this results in the following time format: January 2nd, 3:04:05 PM, 2006 Or in another form: 02.01.2006 03:04:05 PM It is important to remember that this value is nothing more than a regular increasing sequence of numbers without any special significance. Therefore, this date and time act as a predefined layout for working with any explicitly specified date and time values. For example, here’s an abstract (not Go-specific) pseudocode example: currentTime = time.now() console.write("Current date: ", currentTime.format("%D.%M.%Y")) console.write("Current time: ", currentTime.format("%H:%M")) console.write("Current date and time: ", currentTime.format("%D.%M.%Y %H:%M")) In our pseudo-console, this would produce the following pseudo-output: Current date: 26.11.2024 Current time: 14:05 Current date and time: 26.11.2024 14:05 This is how date and time formatting works in most programming languages. In Go, however, the pseudocode would look like this: currentTime = time.now() console.write("Current date: ", currentTime.format("02.01.2006")) console.write("Current time: ", currentTime.format("03:04")) console.write("Current date and time: ", currentTime.format("02.01.2006 03:04")) The console output would be similar: Current date: 26.11.2024 Current time: 14:05 Current date and time: 26.11.2024 14:05 Here, the standard template values for date and time are automatically replaced with the actual date and time values. Additionally, template values have certain variations. For instance, you can specify the month 01 as Jan. Thanks to this approach, Go allows templates to be defined in a more intuitive and human-readable way. Parsing Working with time in Go starts by explicitly specifying it. This can be done using the time parsing function: package main import ( "fmt" // package for console I/O "time" // package for working with time "reflect" // package for determining variable types ) func main() { timeLayout := "2006-01-02" // time layout template timeValue := "2024-11-16" // time value to be parsed timeVariable, err := time.Parse(timeLayout, timeValue) // parsing time value using the template if err != nil { panic(err) // handling possible parsing errors } fmt.Println(timeVariable) // output the parsed time variable to the console fmt.Println(reflect.TypeOf(timeVariable)) // output the type of the time variable } When you run the script, the terminal will display the following output: 2024-11-16 00:00:00 +0000 UTC  time.Time Note that after parsing, a variable of type time.Time is created. This variable stores the parsed time value in its internal format. In the example shown, the time layout and value could be replaced with another equivalent format. func main() { timeLayout := "2006-Jan-02" timeValue:= "2024-Nov-16" ... The final result would remain the same. During parsing, an additional parameter can be specified to set the time zone, also known as the time offset or time zone: package main import ( "fmt" "time" ) func main() { // Local timeLocation, err := time.LoadLocation("Local") if err != nil { panic(err) } timeVariable, err := time.ParseInLocation("2006-01-02 15:04", "2024-11-16 07:45", timeLocation) if err != nil { panic(err) } fmt.Println("Local: ", timeVariable) // Asia/Bangkok timeLocation, err = time.LoadLocation("Asia/Bangkok") if err != nil { panic(err) } timeVariable, err = time.ParseInLocation("2006-01-02 15:04", "2024-11-16 07:45", timeLocation) if err != nil { panic(err) } fmt.Println("Asia/Bangkok: ", timeVariable) // Europe/Nicosia timeLocation, err = time.LoadLocation("Europe/Nicosia") if err != nil { panic(err) } timeVariable, err = time.ParseInLocation("2006-01-02 15:04", "2024-11-16 07:45", timeLocation) if err != nil { panic(err) } fmt.Println("Europe/Nicosia: ", timeVariable) } The console output of this script will be as follows: Local: 2024-11-16 07:45:00 +0000 UTC Asia/Bangkok: 2024-11-16 07:45:00 +0700 +07 Europe/Nicosia: 2024-11-16 07:45:00 +0300 EET Instead of explicitly creating a time zone variable, you can use a predefined constant: package main import ( "fmt" "time" ) func main() { // time.LoadLocation("Local") timeLocation, err := time.LoadLocation("Local") if err != nil { panic(err) } timeVariable, err := time.ParseInLocation("2006-01-02 15:04", "2024-11-16 07:45", timeLocation) if err != nil { panic(err) } fmt.Println(timeVariable) // time.Local timeVariable, err = time.ParseInLocation("2006-01-02 15:04", "2024-11-16 07:45", time.Local) if err != nil { panic(err) } fmt.Println(timeVariable) } In this case, the complete date and time values in both variants will be identical. 2024-11-16 07:45:00 +0000 UTC2024-11-16 07:45:00 +0000 UTC You can find a complete list of available time zones in the so-called Time Zone Database (tz database). Time zone identifiers are specified using two region names separated by a slash. For example: Europe/Nicosia Asia/Dubai US/Alaska Formatting We can format an already created time variable to represent its value as a specific text string. Thus, a variable of type time.Time has built-in methods for converting date and time into a string type. package main import ( "fmt" "time" ) func main() { timeLayout := "2006-01-02 15:04:05" timeValue := "2024-11-15 12:45:20" timeVariable, err := time.Parse(timeLayout, timeValue) if err != nil { panic(err) } fmt.Print("\r", "DATE", "\r\n") fmt.Println(timeVariable.Format("2006-01-02")) fmt.Println(timeVariable.Format("01/02/06")) fmt.Println(timeVariable.Format("01/02/2006")) fmt.Println(timeVariable.Format("20060102")) fmt.Println(timeVariable.Format("010206")) fmt.Println(timeVariable.Format("January 02, 2006")) fmt.Println(timeVariable.Format("02 January 2006")) fmt.Println(timeVariable.Format("02-Jan-2006")) fmt.Println(timeVariable.Format("Jan-02-06")) fmt.Println(timeVariable.Format("Jan-02-2006")) fmt.Println(timeVariable.Format("06")) fmt.Println(timeVariable.Format("Mon")) fmt.Println(timeVariable.Format("Monday")) fmt.Println(timeVariable.Format("Jan-06")) fmt.Print("\r", "TIME", "\r\n") fmt.Println(timeVariable.Format("15:04")) fmt.Println(timeVariable.Format("15:04:05")) fmt.Println(timeVariable.Format("3:04 PM")) fmt.Println(timeVariable.Format("03:04:05 PM")) fmt.Print("\r", "DATE and TIME", "\r\n") fmt.Println(timeVariable.Format("2006-01-02T15:04:05")) fmt.Println(timeVariable.Format("2 Jan 2006 15:04:05")) fmt.Println(timeVariable.Format("2 Jan 2006 15:04")) fmt.Println(timeVariable.Format("Mon, 2 Jan 2006 15:04:05 MST")) fmt.Print("\r", "PREDEFINED FORMATS", "\r\n") fmt.Println(timeVariable.Format(time.RFC1123)) // predefined format fmt.Println(timeVariable.Format(time.Kitchen)) // predefined format fmt.Println(timeVariable.Format(time.Stamp)) // predefined format fmt.Println(timeVariable.Format(time.DateOnly)) // predefined format } Running this script will output various possible date and time formats in the terminal: DATE 2024-11-15 11/15/24 11/15/2024 20241115 111524 November 15, 2024 15 November 2024 15-Nov-2024 Nov-15-24 Nov-15-2024 24 Fri Friday Nov-24 TIME 12:45 12:45:20 12:45 PM 12:45:20 PM DATE and TIME 2024-11-15T12:45:20 15 Nov 2024 12:45:20 15 Nov 2024 12:45 Fri, 15 Nov 2024 12:45:20 UTC PREDEFINED FORMATS Fri, 15 Nov 2024 12:45:20 UTC 12:45PM Nov 15 12:45:20 2024-11-15 Pay attention to the last few formats, which are predefined as constant values. These constants provide commonly used date and time formats in a convenient, ready-to-use form. You can find a complete list of these constants in the official documentation. time.Layout 01/02 03:04:05PM '06 -0700 time.ANSIC Mon Jan _2 15:04:05 2006 time.UnixDate Mon Jan _2 15:04:05 MST 2006 time.RubyDate Mon Jan 02 15:04:05 -0700 2006 time.RFC822 02 Jan 06 15:04 MST time.RFC822Z 02 Jan 06 15:04 -0700 time.RFC850 Monday, 02-Jan-06 15:04:05 MST time.RFC1123 Mon, 02 Jan 2006 15:04:05 MST time.RFC1123Z Mon, 02 Jan 2006 15:04:05 -0700 time.RFC3339 2006-01-02T15:04:05Z07:00 time.RFC3339Nano 2006-01-02T15:04:05.999999999Z07:00 time.Kitchen 3:04PM time.Stamp Jan _2 15:04:05 time.StampMilli Jan _2 15:04:05.000 time.StampMicro Jan _2 15:04:05.000000 time.StampNano Jan _2 15:04:05.000000000 time.DateTime 2006-01-02 15:04:05 time.DateOnly 2006-01-02 time.TimeOnly 15:04:05 Another common method to format date and time in Go is by converting it to Unix time.  package main import ( "fmt" "time" "reflect" ) func main() { timeVariable := time.Unix(350, 50) // set Unix time to 350 seconds and 50 nanoseconds from January 1, 1970, 00:00:00 fmt.Println("Time:", timeVariable) // display time in UTC format timeUnix := timeVariable.Unix() timeUnixNano := timeVariable.UnixNano() fmt.Println("Time (UNIX, seconds):", timeUnix) // display time in Unix format (seconds) fmt.Println("Time (UNIX, nanoseconds):", timeUnixNano) // display time in Unix format (nanoseconds) fmt.Println("Time (type):", reflect.TypeOf(timeUnix)) // display the variable type for Unix time } After running this script, the following output will appear in the terminal: Time: 1970-01-01 00:05:50.00000005 +0000 UTC Time (UNIX, seconds): 350 Time (UNIX, nanoseconds): 350000000050 Time (type): int64 Note that the variable created to store the Unix time value is of type int64, not time.Time. Thus, by using formatting, you can perform conversions between string-based time and Unix time and vice versa: package main import ( "fmt" "time" ) func main() { timeString, _ := time.Parse("2006-01-02 15:04:05", "2024-11-15 12:45:20") fmt.Println(timeString.Unix()) timeUnix := time.Unix(12345, 50) fmt.Println(timeUnix.Format("2006-01-02 15:04:05")) } The console output of this script will display the results of conversions to and from Unix time: 17316747201970-01-01 03:25:45 Creation In Go, there is a more straightforward way to create a time.Time variable by explicitly setting the date and time parameters: package main import ( "fmt" "time" ) func main() { timeLocation, _ := time.LoadLocation("Europe/Vienna") // year, month, day, hour, minute, second, nanosecond, time zone timeVariable := time.Date(2024, 11, 20, 12, 30, 45, 50, timeLocation) fmt.Print(timeVariable) } After running this script, the following output will appear in the terminal: 2024-11-20 12:30:45.00000005 +0100 CET Current Date and Time In addition to manually setting arbitrary dates and times, you can set the current date and time: package main import ( "fmt" "time" "reflect" ) func main() { timeNow := time.Now() fmt.Println(timeNow) fmt.Println(timeNow.Format(time.DateTime)) fmt.Println(timeNow.Unix()) fmt.Println(reflect.TypeOf(timeNow)) } After running this script, the following output will appear in the terminal: 2024-11-27 17:08:18.195495127 +0000 UTC m=+0.000035621 2024-11-27 17:08:18 1732727298 time.Time As you can see, the time.Now() function creates the familiar time.Time variable, whose values can be formatted arbitrarily. Extracting Parameters The time.Time variable consists of several parameters that together form the date and time: Year Month Day Weekday Hour Minute Second Nanosecond Time zone Go provides a set of methods to extract and modify each of these parameters. Most often, you will need to retrieve specific parameters from an already created time variable: package main import ( "fmt" "time" "reflect" ) func main() { timeLayout := "2006-01-02 15:04:05" timeValue := "2024-11-15 12:45:20" timeVariable, _ := time.Parse(timeLayout, timeValue) fmt.Println("Year:", timeVariable.Year()) fmt.Println("Month:", timeVariable.Month()) fmt.Println("Day:", timeVariable.Day()) fmt.Println("Weekday:", timeVariable.Weekday()) fmt.Println("Hour:", timeVariable.Hour()) fmt.Println("Minute:", timeVariable.Minute()) fmt.Println("Second:", timeVariable.Second()) fmt.Println("Nanosecond:", timeVariable.Nanosecond()) fmt.Println("Time zone:", timeVariable.Location()) fmt.Println("") fmt.Println("Year (type):", reflect.TypeOf(timeVariable.Year())) fmt.Println("Month (type):", reflect.TypeOf(timeVariable.Month())) fmt.Println("Day (type):", reflect.TypeOf(timeVariable.Day())) fmt.Println("Weekday (type):", reflect.TypeOf(timeVariable.Weekday())) fmt.Println("Hour (type):", reflect.TypeOf(timeVariable.Hour())) fmt.Println("Minute (type):", reflect.TypeOf(timeVariable.Minute())) fmt.Println("Second (type):", reflect.TypeOf(timeVariable.Second())) fmt.Println("Nanosecond (type):", reflect.TypeOf(timeVariable.Nanosecond())) fmt.Println("Time zone (type):", reflect.TypeOf(timeVariable.Location())) } The console output of this script will be: Year: 2024 Month: November Day: 15 Weekday: Friday Hour: 12 Minute: 45 Second: 20 Nanosecond: 0 Time zone: UTC Year (type): int Month (type): time.Month Day (type): int Weekday (type): time.Weekday Hour (type): int Minute (type): int Second (type): int Nanosecond (type): int Time zone (type): *time.Location Thus, you can individually retrieve specific information about the date and time without needing to format the output before displaying it in the console. Note the types of the retrieved variables — all of them have the int type except for a few: Month (time.Month) Weekday (time.Weekday) Time zone (*time.Location) The last one (time zone) is a pointer. Modification, Addition, and Subtraction Modification You cannot change the parameters of date and time directly in an already created time.Time variable. However, you can recreate the variable with updated values, thus changing the existing date and time: package main import ( "fmt" "time" ) func main() { timeVariable := time.Now() fmt.Println(timeVariable) // year, month, day, hour, minute, second, nanosecond, time zone timeChanged := time.Date(timeVariable.Year(), timeVariable.Month(), timeVariable.Day(), timeVariable.Hour() + 14, timeVariable.Minute(), timeVariable.Second(), timeVariable.Nanosecond(), timeVariable.Location()) fmt.Println(timeChanged) } When running this script, the following output will appear: 2024-11-28 14:35:05.287957345 +0000 UTC m=+0.0000391312024-11-29 04:35:05.287957345 +0000 UTC In this example, 14 hours were added to the current time. This way, you can selectively update the time values in an existing time.Time variable. Change by Time Zone Sometimes, it is necessary to determine what the specified date and time will be in a different time zone. For this, Go provides a special method: package main import ( "fmt" "time" ) func main() { locationFirst, _ := time.LoadLocation("Europe/Nicosia") timeFirst := time.Date(2000, 1, 1, 0, 0, 0, 0, locationFirst) fmt.Println("Time (Europe/Nicosia)", timeFirst) locationSecond, _ := time.LoadLocation("America/Chicago") timeSecond := timeFirst.In(locationSecond) // changing the time zone and converting the date and time based on it fmt.Println("Time (America/Chicago)", timeSecond) } The result of running the script will produce the following console output: Time (Europe/Nicosia) 2000-01-01 00:00:00 +0200 EET Time (America/Chicago) 1999-12-31 16:00:00 -0600 CST Thus, we obtain new date and time values, updated according to the newly specified time zone. Addition and Subtraction Go does not have separate methods for date and time addition. Instead, you can add time intervals to an already created time.Time variable: package main import ( "fmt" "time" ) func main() { // current time timeVariable := time.Now() fmt.Println(timeVariable) // adding 5 days (24 hours * 5 days = 120 hours) timeChanged := timeVariable.Add(120 * time.Hour) fmt.Println(timeChanged) // subtracting 65 days (24 hours * 65 days = 1560 hours) timeChanged = timeVariable.Add(-1560 * time.Hour) fmt.Println(timeChanged) } Running this script will give the following output: 2024-12-05 08:42:01.927334604 +0000 UTC m=+0.000035141 2024-12-10 08:42:01.927334604 +0000 UTC m=+432000.000035141 2024-10-01 08:42:01.927334604 +0000 UTC m=-5615999.999964859 Note that when subtracting a sufficient number of days from the time.Time variable, the month is also modified. Also, the time.Hour variable actually has a special type, time.Duration: package main import ( "fmt" "time" "reflect" ) func main() { fmt.Println(reflect.TypeOf(time.Hour)) fmt.Println(reflect.TypeOf(120* time.Hour)) } The output after running the script will be: time.Durationtime.Duration However, modifying the date and time by adding or subtracting a large number of hours is not very clear. In some cases, it is better to use more advanced methods for changing the time: package main import ( "fmt" "time" ) func main() { timeVariable := time.Now() fmt.Println(timeVariable) // year, month, day timeChanged := timeVariable.AddDate(3, 2, 1) fmt.Println(timeChanged) // day timeChanged = timeChanged.AddDate(0, 0, 15) fmt.Println(timeChanged) // year, month timeChanged = timeChanged.AddDate(5, 1, 0) fmt.Println(timeChanged) // -year, -day timeChanged = timeChanged.AddDate(-2, 0, -10) fmt.Println(timeChanged) } After running this script, the output will look like this: 2024-11-28 17:51:45.769245873 +0000 UTC m=+0.000024921 2028-01-29 17:51:45.769245873 +0000 UTC 2028-02-13 17:51:45.769245873 +0000 UTC 2033-03-13 17:51:45.769245873 +0000 UTC 2031-03-03 17:51:45.769245873 +0000 UTC Subtraction Unlike addition, Go has specialized methods for subtracting one time.Time variable from another. package main import ( "fmt" "time" "reflect" ) func main() { timeFirst := time.Date(2024, 6, 14, 0, 0, 0, 0, time.Local) timeSecond := time.Date(2010, 3, 26, 0, 0, 0, 0, time.Local) timeDeltaSub := timeFirst.Sub(timeSecond) // timeFirst - timeSecond timeDeltaSince := time.Since(timeFirst) // time.Now() - timeFirst timeDeltaUntil := time.Until(timeFirst) // timeFirst - time.Now() fmt.Println("timeFirst - timeSecond =", timeDeltaSub) fmt.Println("time.Now() - timeFirst =", timeDeltaSince) fmt.Println("timeFirst - time.Now() =", timeDeltaUntil) fmt.Println("") fmt.Println(reflect.TypeOf(timeDeltaSub)) fmt.Println(reflect.TypeOf(timeDeltaSince)) fmt.Println(reflect.TypeOf(timeDeltaUntil)) } Console output: timeFirst - timeSecond = 124656h0m0s time.Now() - timeFirst = 4029h37m55.577746026s timeFirst - time.Now() = -4029h37m55.577746176s time.Duration time.Duration time.Duration As you can see, the result of the subtraction is the familiar time.Duration type variable. In fact, the main function for finding the difference is time.Time.Sub(), and the other two are just its derivatives: package main import ( "fmt" "time" ) func main() { timeVariable := time.Date(2024, 6, 14, 0, 0, 0, 0, time.Local) fmt.Println(time.Now().Sub(timeVariable)) fmt.Println(time.Since(timeVariable)) fmt.Println("") fmt.Println(timeVariable.Sub(time.Now())) fmt.Println(time.Until(timeVariable)) } Console output: 4046h10m53.144212707s 4046h10m53.144254987s -4046h10m53.144261117s -4046h10m53.144267597s You can see that the results of these described functions are identical. time.Time.Since() = time.Now().Sub(timeVariable) time.Time.Until() = timeVariable.Sub(time.Now()) Time Durations Individual time intervals (durations) in the time package are represented as a special variable of type time.Duration. Unlike time.Time, they store not full date and time but time intervals. With durations, you can perform some basic operations that modify their time parameters. Parsing Durations A duration is explicitly defined using a string containing time parameters: package main import ( "fmt" "time" ) func main() { // hours, minutes, seconds durationHMS, _ := time.ParseDuration("4h30m20s") fmt.Println("Duration (HMS):", durationHMS) // minutes, seconds durationMS, _ := time.ParseDuration("6m15s") fmt.Println("Duration (MS):", durationMS) // hours, minutes durationHM, _ := time.ParseDuration("2h45m") fmt.Println("Duration (HM):", durationHM) // hours, seconds durationHS, _ := time.ParseDuration("2h10s") fmt.Println("Duration (HS):", durationHS) // hours, minutes, seconds, milliseconds, microseconds, nanoseconds durationFULL, _ := time.ParseDuration("6h50m40s30ms4µs3ns") fmt.Println("Full Duration:", durationFULL) } Output of the script: Duration (HMS): 4h30m20s Duration (MS): 6m15s Duration (HM): 2h45m0s Duration (HS): 2h0m10s Full Duration: 6h50m40.030004003s Note the last duration, which contains all possible time parameters in decreasing order of magnitude—hours, minutes, seconds, milliseconds, microseconds, and nanoseconds. During parsing, each parameter is specified using the following keywords: Hours — h Minutes — m Seconds — s Milliseconds — ms Microseconds — µs Nanoseconds — ns Moreover, the order of specifying duration parameters does not affect it: package main import ( "fmt" "time" ) func main() { duration, _ := time.ParseDuration("7ms20s4h30m") fmt.Println("Duration:", duration) } Terminal output: Duration: 4h30m20.007s Formatting Durations In Go, we can represent the same duration in different units of measurement: package main import ( "fmt" "time" "reflect" ) func main() { duration, _ := time.ParseDuration("4h30m20s") fmt.Println("Duration:", duration) fmt.Println("") fmt.Println("In hours:", duration.Hours()) fmt.Println("In minutes:", duration.Minutes()) fmt.Println("In seconds:", duration.Seconds()) fmt.Println("In milliseconds:", duration.Milliseconds()) fmt.Println("In microseconds:", duration.Microseconds()) fmt.Println("In nanoseconds:", duration.Nanoseconds()) fmt.Println("") fmt.Println(reflect.TypeOf(duration.Hours())) fmt.Println(reflect.TypeOf(duration.Minutes())) fmt.Println(reflect.TypeOf(duration.Seconds())) fmt.Println(reflect.TypeOf(duration.Milliseconds())) fmt.Println(reflect.TypeOf(duration.Microseconds())) fmt.Println(reflect.TypeOf(duration.Nanoseconds())) } Output of the script: Duration: 4h30m20s In hours: 4.5055555555555555 In minutes: 270.3333333333333 In seconds: 16220 In milliseconds: 16220000 In microseconds: 16220000000 In nanoseconds: 16220000000000 float64 float64 float64 int64 int64 int64 As you can see, the parameters for hours, minutes, and seconds are of type float64, while the rest are of type int. Conclusion This guide covered the basic functions for working with dates and times in the Go programming language, all of which are part of the built-in time package. Thus, Go allows you to: Format dates and times Convert dates and times Set time zones Extract specific date and time parameters Set specific date and time parameters Add and subtract dates and times Execute code based on specific time settings For more detailed information on working with the time package, refer to the official Go documentation. In addition, you can deploy Go applications (such as Beego and Gin) on our app platform.
28 January 2025 · 19 min to read

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