Domain layer

The domain layer holds the business logic layer of a module. It typically does not contain resource-specific or database-specific information. Its primary functions include:

• Defining the generic data objects, or models, that contain business logic. This logic defines which operations can be performed on particular types of data, such as a Customer object. These models contain generic information only. Applications can also use SOAP or RESTful endpoints to request data from models.

• (Optionally) Including the implementation of service contracts, although not their definition.

Models

Each domain-layer model contains a reference to a resource model, which it uses to retrieve data from the database with MySql calls. This resource model contains logic for connecting to the underlying database, typically MySQL. A model requires a resource model only if the model data must persist.

Accessing the domain layer

There are three primary ways of accessing a module's domain-layer code:

• Service contracts are the recommended way for one module to access another module's domain-level code. This loosely coupled solution is the optimal way for most modules to access another module.

• A module can directly call into another module. This tightly coupled solution is not recommended for most situations, but is sometimes unavoidable.

• Domain layer code in one module can also plug itself into another module by:

  • event hooks

  • plugins

  • di.xml files (with an SPI contract)

Your strategy for calling another module's domain-layer code is highly dependent upon the unique configuration and needs of your system.

Last updated 9/8/2023

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