# Go Language REST API Part -2

In this article, we'll build a RESTful API in Go language that allows us to perform CRUD (Create, Read, Update, and Delete) operations using all HTTP verbs. We'll use the Gorilla Mux package to handle our routing.

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1680346821506/622946ad-54da-4bb4-9f5d-d59b1e5de77c.png align="center")

## **Setting up the Project**

Before we start, make sure you have Go installed on your system. You can download the latest version of Go from the official website [**https://golang.org/dl/**](https://golang.org/dl/).

To create a new Go project, create a new directory for your project and navigate to it in the terminal. We'll call our project `rest-api`. Inside the `rest-api` directory, create a new file called `main.go`.

Next, we'll install the Gorilla Mux package using the following command:

```go
go get -u github.com/gorilla/mux
```

This will install the package in the `$GOPATH` directory.

## **Defining our Data Model**

In our REST API, we'll be working with a simple data model representing a book. Each book has an ID, title, author, and description. We'll define a struct to represent a book as follows:

```go
type Book struct {
    ID          string `json:"id"`
    Title       string `json:"title"`
    Author      string `json:"author"`
    Description string `json:"description"`
}
```

We'll also create a global variable to store our books:

```go
var books []Book
```

## **Implementing the Endpoints**

### **GET /books**

The first endpoint we'll implement is a `GET` endpoint that retrieves all the books. The endpoint will respond with a JSON array of all the books.

```go
func getBooks(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(books)
}
```

### **GET /books/{id}**

The second endpoint we'll implement is a `GET` endpoint that retrieves a specific book by its ID. The endpoint will respond with a JSON object representing the book.

```go
func getBook(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    params := mux.Vars(r)
    for _, item := range books {
        if item.ID == params["id"] {
            json.NewEncoder(w).Encode(item)
            return
        }
    }
    json.NewEncoder(w).Encode(&Book{})
}
```

### **POST /books**

The third endpoint we'll implement is a `POST` endpoint that creates a new book. The endpoint will accept a JSON object representing the book, generate a new ID for the book, and add it to the list of books.

```go
func createBook(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    var book Book
    _ = json.NewDecoder(r.Body).Decode(&book)
    book.ID = strconv.Itoa(rand.Intn(1000000))
    books = append(books, book)
    json.NewEncoder(w).Encode(book)
}
```

### **PUT /books/{id}**

The PUT method is used to update an existing resource. In this case, we will be updating a book's information using its ID as a parameter. Here's an example:

```go
func updateBook(w http.ResponseWriter, r *http.Request) {
	// Get the book ID from the URL parameter
	params := mux.Vars(r)
	id := params["id"]

	// Check if the book exists
	book, err := getBookByID(id)
	if err != nil {
		w.WriteHeader(http.StatusNotFound)
		return
	}

	// Parse the request body to get the new book information
	var updatedBook Book
	err = json.NewDecoder(r.Body).Decode(&updatedBook)
	if err != nil {
		w.WriteHeader(http.StatusBadRequest)
		return
	}

	// Update the book with the new information
	book.Title = updatedBook.Title
	book.Author = updatedBook.Author
	book.Year = updatedBook.Year

	// Save the updated book to the database
	err = updateBookInDB(book)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
}
```

This function first gets the book ID from the URL parameter using `mux.Vars()`. It then checks if the book exists using the `getBookByID()` function, which retrieves a book from the database by its ID. If the book does not exist, it returns a 404 status code.

The function then parses the request body to get the new book information using `json.NewDecoder()`. If the request body is malformed, it returns a 400 status code.

The book's information is updated with the new information from the request body, and it is saved to the database using `updateBookInDB()`. If there is an error while updating the book, it returns a 500 status code.

Finally, it returns a 200 status code to indicate that the book was successfully updated.

## **DELETE /books/{id}**

The DELETE method is used to delete an existing resource. In this case, we will be deleting a book using its ID as a parameter. Here's an example:

```go
func deleteBook(w http.ResponseWriter, r *http.Request) {
	// Get the book ID from the URL parameter
	params := mux.Vars(r)
	id := params["id"]

	// Check if the book exists
	book, err := getBookByID(id)
	if err != nil {
		w.WriteHeader(http.StatusNotFound)
		return
	}

	// Delete the book from the database
	err = deleteBookFromDB(book)
	if err != nil {
		w.WriteHeader(http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusNoContent)
}
```

This function first gets the book ID from the URL parameter using `mux.Vars()`. It then checks if the book exists using the `getBookByID()` function. If the book does not exist, it returns a 404 status code.

The function then deletes the book from the database using `deleteBookFromDB()`. If there is an error while deleting the book, it returns a 500 status code.

Finally, it returns a 204 status code to indicate that the book was successfully deleted.

I hope this helps, you!!

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