[c#] Repository Pattern Step by Step Explanation

Can someone please explain to me the Repository Pattern in .NET, step by step giving a very simple example or demo.

I know this is a very common question but so far I haven't found a satisfactory answer.

As a summary, I would describe the wider impact of the repository pattern. It allows all of your code to use objects without having to know how the objects are persisted. All of the knowledge of persistence, including mapping from tables to objects, is safely contained in the repository.

Very often, you will find SQL queries scattered in the codebase and when you come to add a column to a table you have to search code files to try and find usages of a table. The impact of the change is far-reaching.

With the repository pattern, you would only need to change one object and one repository. The impact is very small.

Perhaps it would help to think about why you would use the repository pattern. Here are some reasons:

• You have a single place to make changes to your data access

• You have a single place responsible for a set of tables (usually)

• It is easy to replace a repository with a fake implementation for testing - so you don't need to have a database available to your unit tests

There are other benefits too, for example, if you were using MySQL and wanted to switch to SQL Server - but I have never actually seen this in practice!

This is a nice example: The Repository Pattern Example in C#

Basically, repository hides the details of how exactly the data is being fetched/persisted from/to the database. Under the covers:

• for reading, it creates the query satisfying the supplied criteria and returns the result set
• for writing, it issues the commands necessary to make the underlying persistence engine (e.g. an SQL database) save the data