# Retrieving A Book By ID - Planning

Refer back to [*Chapter 6, The Bookstore API Endpoint Specifications, API Endpoint #6: Retrieve a Book Listing*](/part-3/chapter-6/1-the-bookstore-api-endpoint-specifications.md#api-endpoint-5-retrieve-all-book-listings) section for the API endpoint specifications.

## 1 - Route Name

Much like how we planned out the URI for retrieving all books, retrieving a single book is not too far off from that. From the specifications, it seems like this will be a `GET` request that will fetch a single book by its ID. We can refer back to the sections under chapter 3 for guidelines, specifically the sections [*Method Verbs*](/part-2/chapter-3/3-method-verbs.md) and [*URI Design*](/part-2/chapter-3/2-uri-design.md).

The following URI should suffice.

`GET /api/v1/books/:id`

## 2 - Input Request

Similar to retrieving all books, there are none.

## 3 - Middleware

Similar to retrieving all books, there are none.

## 4 - Validation

Similar to retrieving all books, there are none.

## 5 - Domain

Similar to the retrieval of all books, we will be using the same 3 entities to orchestrate our domain logic.

* `bookModel`
* `bookRepository`
* `bookService`

We will definitely use the `bookRepository` and get it a method something like `getById()`.

In the `bookService`, we would want to have a method as well, perhaps, `getBookById()`. Also, remember that we want to do some sort of validation to check if the book we are trying to retrieve exists. Recall that we must return a 404 in our response to indicate that a book with the specified ID by the client does not exist.

## 6 - Events

Similar to retrieving all books, there are none.

## 7 - Response(s)

There are 2 types of responses that could possibly return from this endpoint.

The first is the book with the specified ID if it does exist in the database.

```json
{
    "status": "success",
    "code": 200,
    "message": "Here is the book with the specified ID."
    "data": {
       "id": "61f88350745d83158f3c746d",
       "title": "Harry Potter and the Goblet of Fire",
       "description": "Mint condition, but will negotiate",
       "price": 99,
       "author": "J.K. Rowling",
       "datePublished": "Sun Oct 10 2021 23:56:34 GMT-0400"
    },
    "errors": null
}
```

The second is a message indicating to the client that the book with the specified ID does not exist.

```json
{
    "status": "error",
    "code": 404,
    "message": "That book with the specified ID does not exist."
    "data": null,
    "errors": [
        "Book listing not found."
    ]
}
```


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