1: Practically Designing and API to be An Asset

Any software you design will be used in ways you did not anticipate, that is especially true when you are design API’s which nowadays refers to Web REST APIs. There are different audiences or users for any API. There are the direct API users you know of that are defined in the specifications or solution design/architecture documents, like Web or Mobile clients for example. Then there are the ones you did not anticipate that would come at later stages. For example the API might be used to synchronize data with another system or to extract data for migration to another system. Nowadays, APIs are being considered as assets that would live longer than the projects or systems they are being built for. Taking that into account, there are many things that needs to be considered when designing an API. Let us assume we are designing and API for Authors/Books microservice as shown in the diagram below.

 

 

In the Book Author example, we want to implement CRUD (Create, read, Update and Delete) API for Author and Book entities. The requirements for this API

  1. Search and listing functionality to:
    1. Get a List Authors with various search terms
    2. Get author books
    3. Search books by Author, Genre
  2. Add, update, delete Author or Book

To implement these requirements and have this API as an asset for later use we take the following steps

1: Define the Data type for the API Data Objects

Based on the requirement we first define the schemas for the Author and Book objects that the API will support.

For each resource the API supports we define a schema for:

  1. Data Manipulation Object
  2. Full object
  3. Full Object with HATEOAS (Links for operations)

In RAML we can define those objects as follows :

#%RAML 1.0

title: GT Books API Types

types:


AuthorMod:


description: This is Author for Data Manipulation


type: object


properties:


Name:


required: true


example: Moustafa Refaat


description: Author Name


type: string


Nationality:


required: true


example: Canadian


description: Author Nationality


type: string


Date-of-Birth:


required: true


example: 2018-12-09


description: Author Date of Birth


type: date-only


Date-of-Death:


required: false


example: 2018-12-09


description: Author Date of Death


type: date-only

 


Author:


description: This is the Full Author


type: AuthorMod


properties:


Id:


required: true


example: 1


description: Author Id


type: integer


Age:


required: false


maximum: 200


minimum: 8


example: 10


description: Author Age


type: integer

 


AuthorHateoas:


description: Author with Hateoas information LINKS


type: Author


properties:


Links:


required: true


description: Property description


type: array


items:


required: true


type: Link

 


BookMod:


description:
Book Info for Data Manipulation


type: object


properties:


AuthorId:


required: true


example: 1


description: Author Id


type: integer


Name:


required: true


example: Example


description: Book Name


type: string


Genre:


required: true


example: Example


description: Book Genre


type: string


Stars-Rating:


required: false


maximum: 5


minimum: 0


example: 1


description: Book Rating


type: integer


ISBN:


required: true


example: Example


description: Book ISBN


type: string


PublishDate:


required: true


example: 2018-12-09


description: Book Publish Date


type: date-only

 


Book:


description: Book Info


type: BookMod


properties:


Id:


required: true


example: 1


description: Book Id


type: integer


AuthorName:


required: true


example: Moustafa Refaat


description: Author Name


type: string

 


BookHateoas:


description: Book Information with Hateoas links


type: Book


properties:


Links:


required: true


description: Property description


type: array


items:


required: true


type: Link

 


Link:


description: Hateoas LINK


type: object


properties:


href:


required: true


example: /Book/10


description: URL Link


type: string


rel:


required: true


example: GetBook


description: Operation


type: string


method:


required: true


example: GET


description: HTTP Method Get, PUT,..


type: string

 

2: Define URLs Resources for the API

For each Resource define and implement all the HTTP methods (Get, Post, Put, Delete, Patch, Head, Options) even if you are not going to use them now. You can make the implementation return “403 forbidden” message to the client to indicate that this operation is not supported. For our example we will have

  • /Authors
    • Get: Search/List Authors, return body list of authors matching the search/list criteria with headers containing the paging information
    • Post: Create a new Author, return created author
    • Put: Not Supported return “403 Forbidden” error
    • Delete: Not Supported return “403 Forbidden” error
    • Patch: Not Supported return “403 Forbidden” error
    • Head: Return empty body
    • Options: returns the supported methods by this resource “Get, Post, Head, Options”.
  • /Authors/{id}
    • Get: return author with supplied ID
    • Post: Not Supported return “403 Forbidden” error
    • Put: Update the author and return the updated author
    • Delete: Deletes the author
    • Patch: Not Supported return “403 Forbidden” error
    • Head: Not Supported return “403 Forbidden” error
    • Options: returns “Get, Put, Delete, Options”
  • /Authors/{id}/Books
    • Get: Search/List of books for Author, return body list of books matching the search/list criteria with headers containing the paging information
    • Post: Create a new book for author with Id returns created Book
    • Put: Not Supported return “403 Forbidden” error
    • Delete: Not Supported return “403 Forbidden” error
    • Patch: Not Supported return “403 Forbidden” error
    • Head: Returns same as Get with empty body
    • Options: Returns “Get, Post, Head, Options”
  • /Books
    • Get: Search/List of books, return body list of books matching the search/list criteria with headers containing the paging information
    • Post: Create a new book for author with Id returns created Book
    • Put: Not Supported return “403 Forbidden” error
    • Delete: Not Supported return “403 Forbidden” error
    • Patch: Not Supported return “403 Forbidden” error
    • Head: returns same as Get with empty body
    • Options: returns “Get, Post, Head, Options”
  • /Books/{id}
    • Get: Returns the book with ID
    • Post: Not Supported return “403 Forbidden” error
    • Put: update the book
    • Delete: Deletes the book
    • Patch: Not Supported return “403 Forbidden” error
    • Head: Not Supported return “403 Forbidden” error
    • Options: returns “Get, Put, Delete, Options”

 

To be continued…

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