The Repository Pattern is a common construct to avoid duplication of data access logic throughout our application. This includes direct access to a database, ORM, WCF dataservices, xml files and so on. The sole purpose of the repository is to hide the nitty gritty details of accessing the data. We can easily query the repository for data objects, without having to know how to provide things like a connection string. The repository behaves like a freely available in-memory data collection to which we can add, delete and update objects.
The Repository pattern adds a separation layer between the data and domain layers of an application. It also makes the data access parts of an application better testable.
The example below show an interface of a generic repository of type T, which is a LINQ to SQL entity. It provides a basic interface with operations like Insert, Delete, GetById and GetAll. The SearchFor operation takes a lambda expression predicate to query for a specific entity.
The implementation of the IRepository interface is pretty straight forward. In the constructor we retrieve the repository entity by calling the datacontext GetTable(of type T) method. The resulting Table(of type T) is the entity table we work with in the rest of the class methods. e.g. SearchFor() simply calls the Where operator on the table with the predicate provided.
// Sidenote: the == operator throws NotSupported Exception!
The generic GetById() method explicitly needs all our entities to implement the IEntity interface. This is because we need them to provide us with an Id property to make our generic search for a specific Id possible.
Since we already have LINQ to SQL entities with an Id property, declaring the IEntity interface is sufficient. Since these are partial classes, they will not be overridden by LINQ to SQL code generation tools.
We are now ready to use the generic repository in an application.
The code below shows a nice and clean implementation of the generic repository pattern for the Entity Framework. There’s no need for the IEntity interface here since we use the convenient Find extension method of the DbSet class. Thanks to my co-worker Frank van der Geld for helping me out.
You are currently reading The Repository Pattern Example in C# at Naik Vinay.