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C# Entity Framework Query

Building an EF Core Query

C# EF Core query retrieves data with LINQ expressions.

Introduction to Entity Framework Core Queries

Entity Framework Core (EF Core) is a powerful Object-Relational Mapper (ORM) for .NET, which simplifies database access. EF Core enables developers to work with a database using .NET objects, eliminating the need for most of the data-access code that developers usually need to write.

A key feature of EF Core is its ability to query data using Language Integrated Query (LINQ). LINQ provides a consistent syntax for querying various data sources, including databases, making it easier to write and understand queries.

Setting Up EF Core in a C# Project

To use EF Core in your C# project, you need to install the necessary NuGet packages. You can do this using the NuGet Package Manager in Visual Studio or by running the following command in the Package Manager Console:

Defining the Data Model

Before querying data, you need to define your data model. This typically includes defining entity classes and a derived context class. For example, a simple model for a blogging application might look like this:

Querying Data with LINQ

Once you have your data model set up, you can start querying data using LINQ. Here's an example of how to retrieve all the blogs from the database:

In this example, context.Blogs.ToList() is a LINQ query that retrieves all the blogs from the database. The ToList() method executes the query and returns the results as a list.

Filtering and Sorting Data

LINQ also allows you to filter and sort data. For example, you can retrieve blogs whose URLs contain a specific substring and order them by their ID:

In this example, the Where method filters the blogs to include only those whose URLs contain the string "example". The OrderBy method sorts the results by BlogId.

Eager Loading Related Data

EF Core supports eager loading, which allows you to load related data as part of the initial query. This is done using the Include method. Here's how you can load blogs along with their related posts:

The Include method tells EF Core to include the related Posts when it retrieves the Blogs. This is useful when you need to work with both entities simultaneously.

Conclusion

Entity Framework Core provides a robust way to interact with databases using C#. By leveraging LINQ, developers can write expressive and efficient queries that are easy to maintain. Understanding how to query data effectively using EF Core is an essential skill for any C# developer working with databases.

Examples