Multi Layered

Solution Structure

• Do create a separated Visual Studio solution for every module.

• Do name the solution as CompanyName.ModuleName (for core ABP modules, it's Volo.Abp.ModuleName).

• Do develop the module as layered, so it has several packages (projects) those are related to each other.

  • Every package has its own module definition file and explicitly declares the dependencies for the depended packages/modules.

Layers & Packages

The following diagram shows the packages of a well-layered module and dependencies of those packages between them:

The ultimate goal is to allow an application to use the module in a flexible manner. Example applications:

• A) A monolithic application;

  • Adds references to the Web and the Application packages.

  • Adds a reference to one of the EF Core or the MongoDB packages based on the preference.

  • The result;

    • The application can show UI of the module.

    • It hosts the application and domain layers in the same process (that's why it needs to have a reference to a database integration package).

    • This application also serves the module's HTTP API (since it includes the HttpApi package through the Web package).

• B) An application that just serves the module as a microservice;

  • Adds a reference to HttpApi and Application packages.

  • Adds a reference to one of the EF Core or the MongoDB packages based on the preference.

  • The result;

    • The application can not show UI of the module since it does not have a reference to the Web package.

    • It hosts the application and domain layers in the same process (that's why it needs to have a reference to a database integration package).

    • This application serves the module's HTTP API (as the main goal of the application).

• C) An application that shows the module UI but does not host the application (just uses it as a remote service that is hosted by the application A or B);

  • Adds a reference to the Web and the HttpApi.Client packages.

  • Configures the remote endpoint for the HttpApi.Client package.

  • The result;

    • The application can show UI of the module.

    • It does not host the application and domain layers of the module in the same process. Instead, uses it as a remote service.

    • This application also serves the module's HTTP API (since it includes the HttpApi package through the Web package).

• D) A client application (or microservice) that just uses the module as a remote service (that is hosted by the application A, B or C);

  • Adds a reference to the HttpApi.Client package.

  • Configures the remote endpoint for the HttpApi.Client package.

  • The result;

    • The application can use all the functionality of the module as a remote client.

    • The application is just a client and can not serve the HTTP API of the module.

    • The application is just a client and can not show the UI of the module.

• E) A proxy application that hosts the HTTP API of the module but just forwards all requests to another application (that is hosted by the application A, B or C);

  • Adds a reference to the HttpApi and HttpApi.Client packages.

  • Configures the remote endpoint for the HttpApi.Client package.

  • The result;

    • The application can use all the functionality of the module as a remote client.

    • This application also serves the module's HTTP API, but actually works just like a proxy by redirecting all requests (for the module) to another remote server.

Next section describes the packages in more details.

Domain Layer

• Do divide the domain layer into two projects:

  • Domain.Shared package, named as CompanyName.ModuleName.Domain.Shared, that contains constants, enums and other types those can be safely shared with the all layers of the module. This package can also be shared to 3rd-party clients. It can not contain entities, repositories, domain services or any other business objects.

  • Domain package, named as CompanyName.ModuleName.Domain, that contains entities, repository interfaces, domain service interfaces and their implementations and other domain objects.

    • Domain package depends on the Domain.Shared package.

Application Layer

• Do divide the application layer into two projects:

  • Application.Contracts package, named as CompanyName.ModuleName.Application.Contracts, that contains application service interfaces and related data transfer objects.

    • Application contract package depends on the Domain.Shared package.

  • Application package, named as CompanyName.ModuleName.Application, that contains application service implementations.

    • Application package depends on the Domain and the Application.Contracts packages.

Infrastructure Layer

• Do create a separated integration package for each ORM/database integration like Entity Framework Core and MongoDB.

  • Do, for instance, create a CompanyName.ModuleName.EntityFrameworkCore package that abstracts the Entity Framework Core integration. ORM integration packages depend on the Domain package.

  • Do not depend on other layers from the ORM/database integration package.

• Do create a separated integration package for each major library that is planned to be replaceable by another library without effecting the other packages.

HTTP Layer

• Do create an HTTP API package, named as CompanyName.ModuleName.HttpApi, to develop a REST style HTTP API for the module.

  • HTTP API package only depends on the Application.Contracts package. It does not depend on the Application package.

  • Do create a Controller for each application service (generally by implementing their interfaces). These controllers uses the application service interfaces to delegate the actions. It just configures routes, HTTP methods and other web related stuffs if needed.

• Do create an HTTP API Client package, named as CompanyName.ModuleName.HttpApi.Client, to provide client services for the HTTP API package. Those client services implement application interfaces as clients to a remote endpoint.

  • HTTP API Client package only depends on the Application.Contracts package.

  • Do use dynamic HTTP C# client proxy feature of the ABP.

Web Layer

• Do create a Web package, named as CompanyName.ModuleName.Web, that contains pages, views, scripts, styles, images and other UI components.

  • Web package only depends on the HttpApi package.