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.

B. The Service Layer (Business Logic)

Implements business validation and orchestrates repositories.

unit Service.Customer;

interface

uses
  System.JSON;

type
  TCustomerService = class
  public
    class function GetCustomer(const AId: Integer): TJSONObject;
  end;

implementation

uses
  Repository.Customer, System.SysUtils;

class function TCustomerService.GetCustomer(const AId: Integer): TJSONObject;
begin
  if AId <= 0 then
    raise Exception.Create('Invalid Customer ID');
    
  Result := TCustomerRepository.FindById(AId);
  
  if not Assigned(Result) then
    raise Exception.Create('Customer not found');
end;

end.

C. The Controller Layer (HTTP Transport Adapter)

The ONLY layer that depends on Horse. It parses incoming requests, calls services, and formats HTTP responses.

unit Controller.Customer;

interface

uses
  Horse;

type
  TCustomerController = class
  private
    class procedure GetCustomerHandler(Req: THorseRequest; Res: THorseResponse);
  public
    class procedure RegisterRoutes;
  end;

implementation

uses
  Service.Customer, System.JSON, System.SysUtils, Horse.Commons;

class procedure TCustomerController.RegisterRoutes;
begin
  THorse.Get('/customers/:id', GetCustomerHandler);
end;

class procedure TCustomerController.GetCustomerHandler(Req: THorseRequest; Res: THorseResponse);
var
  LId: Integer;
  LCustomer: TJSONObject;
begin
  try
    LId := Req.Params.Field('id').AsInteger;
    
    // Invocate Business Service (No Horse dependencies passed!)
    LCustomer := TCustomerService.GetCustomer(LId);
    
    Res.Send(LCustomer);
  except
    on E: Exception do
      Res.Status(THTTPStatus.BadRequest).Send(TJSONObject.Create(TJSONPair.Create('error', E.Message)));
  end;
end;

end.
unit

D. The Bootstrap (.dpr)

Now, your main bootstrap file only handles middleware setup and controller registration, keeping it extremely clean:

program MyAPI;

{$APPTYPE CONSOLE}

uses
  Horse,
  Horse.Jhonson,
  Controller.Customer;

begin
  THorse.Use(Jhonson);

  // Register all Controller routes
  TCustomerController.RegisterRoutes;

  THorse.Listen(9000);
end.