horse-mvc-architecture

Horse MVC Architecture

For large-scale, production-ready REST APIs, avoid placing business logic inside route handlers or keeping everything in the .dpr bootstrap file. Implement a clean, decoupled MVC (Model-View-Controller) architecture.

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1. Project Directory Structure

Keep your project organized by dividing concerns into dedicated directories under the src/ folder:

my_project/
├── my_project.dpr
└── src/
    ├── controllers/   # Mappings of HTTP endpoints to service invocations
    ├── services/      # Core business rules, validations, and orchestration
    ├── repositories/  # Database access layer (SQL execution, FireDAC queries)
    └── models/        # Entity classes and data structures (Domain)

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2. Decoupling Rules (The Golden Rule)

To ensure testability and maintenance, never couple your business logic to the web framework.

• Rule: The Service, Repository, and Model layers must never import Horse units or reference Horse objects (like THorseRequest or THorseResponse).
• Reason: If you decide to migrate from HTTP to a CLI application or gRPC, your business services and repositories remain 100% untouched.

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3. Implementation Blueprint

A. The Repository Layer (Database Access)

Retrieves and updates raw database data. It knows nothing about HTTP.

unit Repository.Customer;

interface

uses
  System.JSON, FireDAC.Comp.Client;

type
  TCustomerRepository = class
  public
    class function FindById(const AId: Integer): TJSONObject;
  end;

implementation

class function TCustomerRepository.FindById(const AId: Integer): TJSONObject;
var
  LConnection: TFDConnection;
  LQuery: TFDQuery;
begin
  Result := nil;
  LConnection := TFDConnection.Create(nil);
  LQuery := TFDQuery.Create(nil);
  try
    LConnection.ConnectionDefName := 'MyPooledDef';
    LConnection.Connected := True;
    
    LQuery.Connection := LConnection;
    LQuery.SQL.Text := 'SELECT id, name, email FROM customers WHERE id = :id';
    LQuery.ParamByName('id').AsInteger := AId;
    LQuery.Open;
    
    if not LQuery.IsEmpty then
      Result := LQuery.ToJSONObject; // Returns raw JSON entity
  finally
    LQuery.Free;
    LConnection.Free;
  end;
end;

end.