Using Entity Framework Core for Data Access & Relational Mapping/

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Projection and Grouping Query Operations

Projection and Grouping Query Operations

Learn the basics of projection, and grouping query operations in LINQ.

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Overview

In this lesson, we’ll review how to project and group queries in LINQ using query syntax and query methods.

Projection

Projection is the operation of transforming an object into a new form. This new form often consists only of those properties that get used subsequently.

When using query syntax, we use the select clause for projecting. The select clause determines the values produced when we execute a query. It is common to terminate an expression with it.

We use the C# console app project below to demonstrate:

{
    "version": "0.2.0",
    "configurations": [
        {
            // Use IntelliSense to find out which attributes exist for C# debugging
            // Use hover for the description of the existing attributes
            // For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
            "name": ".NET Core Launch (console)",
            "type": "coreclr",
            "request": "launch",
            "preLaunchTask": "build",
            // If you have changed target frameworks, make sure to update the program path.
            "program": "${workspaceFolder}/bin/Debug/net6.0/QueryData.dll",
            "args": [],
            "cwd": "${workspaceFolder}",
            // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
            "console": "internalConsole",
            "stopAtEntry": false
        },
        {
            "name": ".NET Core Attach",
            "type": "coreclr",
            "request": "attach"
        }
    ]
}
Projection query operations

Click the “Run” button above, then execute the command below:

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dotnet run

Below is a snippet from the output:

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 LASTNAME        SALARY
  Donald          7000
  Yemi            5400
  Fraser          4300
  Blaze           6100

Note the following:

  • The example uses an Employee type highlighted on lines ...