The repository and Unit of Work patterns

The repository pattern is an entity-centric approach to the definition of the domain layer interfaces: each aggregate has its own repository interface that defines how to retrieve and save it, and that defines all queries that involve entities in the aggregate. The data layer implementation of each repository interface is called a repository.

With the repository pattern, each operation has an easy-to-find place where it must be defined: the interface of the aggregate the operation works on, or, in case of a query, the aggregate that contains the root entity of the query.

Often, application layer operations that span several aggregates and that, accordingly, use several different repository interfaces must be executed in a unique transaction. The Unit of Work pattern is a solution that maintains the independence of the domain layer from the underlying data layer. It states that each repository interface must also contain a reference...