Repositories

Sometimes, it is necessary to interact with any type of persistence system in an application. Such a persistence system may be a SQL or NoSQL database, a file, or even an external service. There should be a mechanism that allows us to interact with these systems. The important point here is that the business logic remains separate from the repository-connections logic.

What are repositories?

A repository does not necessarily involve a database. A repository is a pattern, which isolates business logic from data-store-interaction logic. It functions as a collection of objects in memory. It conceals the storage-level details needed for management and query of the information of an aggregate in the underlying data tier. When an aggregate wants to interact with information outside of itself, it invokes functions in a repository. It only knows a group of objects in memory. It is unaware of what lies behind such a repository.