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Message Body Readers and Writers ​

Message Body Readers and Writers are crucial components in WiRL, serving as the bridge between HTTP request/response bodies and your application's data structures. They enable seamless conversion between various data formats and your Delphi objects, allowing you to focus on your business logic rather than low-level data parsing.

How They Work ​

When you define a resource in WiRL, like this:

pascal
[Path('order')]
TOrderResource = class
public
  [POST]
  [Consumes(TMediaType.APPLICATION_JSON)]
  [Produces(TMediaType.APPLICATION_JSON)]
  function PostOrder([BodyParam] AOrderProposal: TOrderProposal): TOrder;
end;

WiRL uses Message Body Readers and Writers to handle the incoming and outgoing data:

  1. Message Body Reader: When a request arrives, WiRL looks for a reader that can transform the incoming JSON (specified by Consumes(TMediaType.APPLICATION_JSON)) into a TOrderProposal object.

  2. Your Business Logic: WiRL then calls your PostOrder method with the created TOrderProposal.

  3. Message Body Writer: After your method returns a TOrder object, WiRL finds a writer to convert it back to JSON (as specified by Produces(TMediaType.APPLICATION_JSON)).

Content Negotiation ​

WiRL supports multiple Consumes and Produces attributes on a single resource. It selects the appropriate reader or writer based on the request's Content-Type and Accept headers, allowing your API to be flexible with different data formats.

Built-in Readers and Writers ​

WiRL provides a variety of pre-built Message Body Readers and Writers:

  1. Core Types (WiRL.Core.MessageBody.Default):

    • Handles strings, simple types (integer, double, etc.), arrays, records, and objects (via the Neon library plugin).
    • Supports streams and MultipartFormData.

  2. Data-aware Types (WiRL.Data.MessageBody.Default):

    • Manages DataSets, DataSet arrays, and conversions to XML and CSV.

  3. FireDAC Specific (WiRL.Data.FireDAC.MessageBody.Default):

    • Provides readers and writers tailored for FireDAC components.

Using Built-in Readers and Writers ​

To use these pre-built components, simply include the necessary units in your project:

pascal
uses
  WiRL.Core.MessageBody.Default,
  WiRL.Data.MessageBody.Default,
  WiRL.Data.FireDAC.MessageBody.Default;

This inclusion automatically registers the readers and writers with WiRL, making them available for use in your resources.

Custom Readers and Writers ​

While WiRL provides a comprehensive set of built-in readers and writers, you can also create custom ones for specific needs. This allows you to handle unique data formats or complex object transformations tailored to your application.

Conclusion ​

Message Body Readers and Writers in WiRL provide a powerful abstraction layer, handling the complexities of data transformation between HTTP and your application's domain objects. By leveraging these components, you can create clean, type-safe REST APIs while maintaining flexibility in data formats and focusing on your core business logic.