Using Entity Framework Core for Data Access & Relational Mapping/

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Loading Related Data

Loading Related Data

Learn how to load related data via the navigational properties of entities in an EF Core model.

We'll cover the following...

Overview

In this lesson, we’ll review strategies for loading related entities via the navigational properties of entities in EF Core. There are three common patterns:

  • Eager loading
  • Explicit loading
  • Lazy loading

The differences between these patterns are related to how and when EF Core translates the queries to the database.

Eager loading

Eager loading loads related data from the database as part of the initial query. It allows us to fetch related entities and prevent additional round-trips to the database. Eager loading uses the Include method to specify the related data.

We’ll demonstrate eager loading using the C# console project below:

{
    "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"
        }
    ]
}
Eager loading related data

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

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dotnet run

Below is a snippet from the output:

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SELECT "e"."Id", "e"."Age", "e"."FirstName", "e"."LastName", "s"."Id", "s"."City", "s"."EmployeeId", "s"."HouseNumber"        
FROM "Employees" AS "e"
LEFT JOIN "Studios" AS "s" ON "e"."Id" = "s"."EmployeeId"

Among the other files in the project is a SQL file named Artists.sql. This file holds the schema and prepopulated data for our Artists database. The database has the following tables:

  • Employees: This stores the music artists’ names and ages.

  • Studios: This stores the studio addresses where the music artists work.

  • Albums: This stores albums released by the music artists. ...