Build RESTful API service in golang using gin-gonic framework

Today I’m going to build a simple API for todo application with the golang programming language. I’m going to use golang simplest/fastest framework gin-gonic and a beautiful ORM gorm for our database work. To install these packages go to your workspace $GOPATH/src and run these command below:

$ go get gopkg.in/gin-gonic/gin.v1
$ go get -u github.com/jinzhu/gorm
$ go get github.com/go-sql-driver/mysql

In generic crud application we need the API’s as follows:

POST todos/
GET todos/
GET todos/{id}
PUT todos/{id}
DELETE todos/{id}

Let’s start coding, go to your $GOPATH/src and make a directory todo. Inside the todo directory create a file main.go. Import the “gin framework” to our project and create the routes like below inside main function. I like to add a prefix of the apis like “api/v1/”, that’s why we’ll use the router Group method

package main

import (
	"github.com/gin-gonic/gin"
)

func main() {
	router := gin.Default()
	v1 := router.Group("/api/v1/todos")
	{
		v1.POST("/", createTodo)
		v1.GET("/", fetchAllTodo)
		v1.GET("/:id", fetchSingleTodo)
		v1.PUT("/:id", updateTodo)
		v1.DELETE("/:id", deleteTodo)
	}
	router.Run()
}

We have created five routes and they handle some functions like createTodo, fetchAllTodo etc. We’ll discuss about them soon. Now we need to setup a database connection. To use database pull the gorm package and mysql dialects in our code. Follow the code below:

package main

import (
	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/mysql"
)

var db *gorm.DB

func init() {
	//open a db connection
	var err error
	db, err = gorm.Open("mysql", "root:12345@/demo?charset=utf8&parseTime=True&loc=Local")
	if err != nil {
		panic("failed to connect database")
	}
	//Migrate the schema
	db.AutoMigrate(&todoModel{})
}

In the above code “mysql” is our database driver, “root” is database username, “12345” password and “demo” is database name. Please change these information as your needs. We’ll use the Database function to get the database connection. Lets make a todoModel and transformedTodo struct. The first struct will represent the original Todo and the second one will hold the transformed todo for response to the api. Here we transformed the todo response because we don’t expose some database fields (updated_at, created_at) to the consumer.

type (
	// todoModel describes a todoModel type
	todoModel struct {
		gorm.Model
		Title     string `json:"title"`
		Completed int    `json:"completed"`
	}
	// transformedTodo represents a formatted todo
	transformedTodo struct {
		ID        uint   `json:"id"`
		Title     string `json:"title"`
		Completed bool   `json:"completed"`
	}
)

Todo struct has one field extra gorm.Model what does it mean? well, this field will embed a Model struct for us which contains four fields “ID, CreatedAt, UpdatedAt, DeletedAt”

Gorm has migration facilities, we already used it in init function. When we run the application first it’ll create a connection and then the migration.

//Migrate the schema
 db.AutoMigrate(&todoModel{})

Can you remember the five routes we wrote a minute earlier? Lets implement the five methods one by one. When a user send a POST request to the path ‘api/v1/todos/’ with ‘title and completed’ field it’ll be handled by this route v1.POST(“/”, createTodo)

Lets Implement the createTodo function

// createTodo add a new todo
func createTodo(c *gin.Context) {
	completed, _ := strconv.Atoi(c.PostForm("completed"))
	todo := todoModel{Title: c.PostForm("title"), Completed: completed}
	db.Save(&todo)
	c.JSON(http.StatusCreated, gin.H{"status": http.StatusCreated, "message": "Todo item created successfully!", "resourceId": todo.ID})
}

In the above code we use gin Context to receive the posted data and gorm database connection to save the todo. After saving the resource we send the resource id with a good & meaningful response to the user.

Lets implement the rest of the functions

// fetchAllTodo fetch all todos
func fetchAllTodo(c *gin.Context) {
	var todos []todoModel
	var _todos []transformedTodo
	db.Find(&todos)
	if len(todos) <= 0 {
		c.JSON(http.StatusNotFound, gin.H{"status": http.StatusNotFound, "message": "No todo found!"})
		return
	}
	//transforms the todos for building a good response
	for _, item := range todos {
		completed := false
		if item.Completed == 1 {
			completed = true
		} else {
			completed = false
		}
		_todos = append(_todos, transformedTodo{ID: item.ID, Title: item.Title, Completed: completed})
	}
	c.JSON(http.StatusOK, gin.H{"status": http.StatusOK, "data": _todos})
}

// fetchSingleTodo fetch a single todo
func fetchSingleTodo(c *gin.Context) {
	var todo todoModel
	todoID := c.Param("id")
	db.First(&todo, todoID)
	if todo.ID == 0 {
		c.JSON(http.StatusNotFound, gin.H{"status": http.StatusNotFound, "message": "No todo found!"})
		return
	}
	completed := false
	if todo.Completed == 1 {
		completed = true
	} else {
		completed = false
	}
	_todo := transformedTodo{ID: todo.ID, Title: todo.Title, Completed: completed}
	c.JSON(http.StatusOK, gin.H{"status": http.StatusOK, "data": _todo})
}

// updateTodo update a todo
func updateTodo(c *gin.Context) {
	var todo todoModel
	todoID := c.Param("id")
	db.First(&todo, todoID)
	if todo.ID == 0 {
		c.JSON(http.StatusNotFound, gin.H{"status": http.StatusNotFound, "message": "No todo found!"})
		return
	}
	db.Model(&todo).Update("title", c.PostForm("title"))
	completed, _ := strconv.Atoi(c.PostForm("completed"))
	db.Model(&todo).Update("completed", completed)
	c.JSON(http.StatusOK, gin.H{"status": http.StatusOK, "message": "Todo updated successfully!"})
}

// deleteTodo remove a todo
func deleteTodo(c *gin.Context) {
	var todo todoModel
	todoID := c.Param("id")
	db.First(&todo, todoID)
	if todo.ID == 0 {
		c.JSON(http.StatusNotFound, gin.H{"status": http.StatusNotFound, "message": "No todo found!"})
		return
	}
	db.Delete(&todo)
	c.JSON(http.StatusOK, gin.H{"status": http.StatusOK, "message": "Todo deleted successfully!"})
}

In the fetchAllTodo function we fetched all the todos and and build a transformed response with id, title, completed . We removed the CreatedAt, UpdatedAt, DeletedAt fields and cast the integer value to bool.

Well, we write enough code, let try to build the app and test it, I’m going test it using chrome extension Postman (you can use any REST client like curl to test).

To build the app open your terminal and go the the project directory

$ go build main.go

The command will build a binary file main and to run the file us this command $ ./main . Wow, our simple todo app is running on port: 8080. It’ll display the debug log, because by default gin run’s in debug mode and port 8080.

Need full source code?#

Need full source code?