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Session12 (#55)
* Initialized session 12 samples * Completed sample EF context interactions * Added notes and migrations to show relations in database * updated with final state after broadcast
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‎sessions/0110-UnitTests/.vscode/settings.json

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{
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"dotnet-test-explorer.testProjectPath": "**/*Test.@(csproj|vbproj|fsproj)",
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"dotnet-test-explorer.autoWatch": true,
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"dotnet-test-explorer.showCodeLens": true
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}

‎sessions/0112-EfCore/.vscode/launch.json

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{
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// Use IntelliSense to find out which attributes exist for C# debugging
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// Use hover for the description of the existing attributes
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// For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
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"version": "0.2.0",
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"configurations": [
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{
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"name": ".NET Core Launch (console)",
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"type": "coreclr",
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"request": "launch",
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"preLaunchTask": "build",
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// If you have changed target frameworks, make sure to update the program path.
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"program": "${workspaceFolder}/SampleEntityFramework/bin/Debug/net5.0/SampleEntityFramework.dll",
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"args": [],
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"cwd": "${workspaceFolder}/SampleEntityFramework",
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// For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
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"console": "internalConsole",
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"stopAtEntry": false
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},
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{
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"name": ".NET Core Attach",
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"type": "coreclr",
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"request": "attach",
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"processId": "${command:pickProcess}"
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}
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]
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}

‎sessions/0112-EfCore/.vscode/tasks.json

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{
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"version": "2.0.0",
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"tasks": [
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{
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"label": "build",
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"command": "dotnet",
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"type": "process",
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"args": [
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"build",
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"${workspaceFolder}/SampleEntityFramework/SampleEntityFramework.csproj",
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"/property:GenerateFullPaths=true",
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"/consoleloggerparameters:NoSummary"
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],
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"problemMatcher": "$msCompile"
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},
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{
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"label": "publish",
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"command": "dotnet",
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"type": "process",
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"args": [
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"publish",
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"${workspaceFolder}/SampleEntityFramework/SampleEntityFramework.csproj",
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"/property:GenerateFullPaths=true",
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"/consoleloggerparameters:NoSummary"
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],
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"problemMatcher": "$msCompile"
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},
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{
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"label": "watch",
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"command": "dotnet",
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"type": "process",
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"args": [
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"watch",
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"run",
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"${workspaceFolder}/SampleEntityFramework/SampleEntityFramework.csproj",
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"/property:GenerateFullPaths=true",
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"/consoleloggerparameters:NoSummary"
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],
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"problemMatcher": "$msCompile"
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}
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]
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}

‎sessions/0112-EfCore/0112-EfCore.sln

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Microsoft Visual Studio Solution File, Format Version 12.00
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# Visual Studio 15
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VisualStudioVersion = 15.0.26124.0
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MinimumVisualStudioVersion = 15.0.26124.0
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SampleEntityFramework", "SampleEntityFramework\SampleEntityFramework.csproj", "{912529D4-72BB-41C7-96BA-B4B8DE8740EC}"
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EndProject
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Global
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GlobalSection(SolutionConfigurationPlatforms) = preSolution
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Debug|Any CPU = Debug|Any CPU
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Debug|x64 = Debug|x64
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Debug|x86 = Debug|x86
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Release|Any CPU = Release|Any CPU
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Release|x64 = Release|x64
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Release|x86 = Release|x86
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EndGlobalSection
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GlobalSection(SolutionProperties) = preSolution
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HideSolutionNode = FALSE
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EndGlobalSection
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GlobalSection(ProjectConfigurationPlatforms) = postSolution
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|x64.ActiveCfg = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|x64.Build.0 = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|x86.ActiveCfg = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Debug|x86.Build.0 = Debug|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|Any CPU.Build.0 = Release|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|x64.ActiveCfg = Release|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|x64.Build.0 = Release|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|x86.ActiveCfg = Release|Any CPU
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{912529D4-72BB-41C7-96BA-B4B8DE8740EC}.Release|x86.Build.0 = Release|Any CPU
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EndGlobalSection
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EndGlobal

‎sessions/0112-EfCore/README.md

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# Session 12 - Entity Framework Core and Data
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We've worked with all sorts of in-memory data storage, manipulation and retrieval up to this point. Let's start working with a database and write some content to disk. In .NET, we use Entity Framework Core to interact with relational databases. While this isn't the only way that you can interact with a database, its the preferred way by many because of the ease of use of Entity Framework Core as an object-relational mapper to convert our object interactions into actions to take against database records.
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## The Setup
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Let's create a console application as a test-bed for interacting with a database. Additionally, to ensure that these samples work on every platform and require no additional setup, we will use SQLite (a file-based database) to persist our data.
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We can add EntityFramework Core to our project with these commands:
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```
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dotnet add package Microsoft.EntityFrameworkCore
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dotnet add package Microsoft.EntityFrameworkCore.Tools
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dotnet add package Microsoft.EntityFrameworkCore.Sqlite
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```
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This will fetch the NuGet package containing the libraries and all of the tools for working with our database and add them to our project.
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## Introducing DbContext
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DbContext is your gateway to the database. A descendent of this class contains table references and configuration to connect to your database. There are two ways to work with this class:
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- Create the class and its classes to work with FIRST, called "Code First"
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- Extract a definition and class hierarchy from your existing database, called "Data First"
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### Defining a class to be stored in a table
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We'll focus on a Code First approach to working with the database. In this sample, we'll manage a database for our blog. Let's create a simple Blogpost type:
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```c#
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public class BlogPost {
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public int Id { get; set; }
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public string Title { get; set; }
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public DateTime PublishedUtc { get; set; }
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public string Content { get; set; }
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public override string ToString() {
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return $"{Title} ({Id})";
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}
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}
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```
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We can create a `DbContext` for our blog and add a property of type `DbSet<BlogPost>` to define a table to be created for our `BlogPost` objects:
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```c#
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public class AppDbContext : DbContext
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{
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public DbSet<BlogPost> Posts { get; set; }
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}
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```
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When we want to interact with the `BlogPost` objects in the database, we'll reach into the `Posts` property and use standard LINQ queries as well as collection interactions to add, update, and delete records from the database.
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## EF Tools
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With these C# classes created, how do we complete the connection to the database? Enter the ef tools. These are global tools that run at the command-line and allow you to manage the connection and definition of the database your code will work with.
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### Installation
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You can intsall the latest version of the ef tools using the following command:
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```
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dotnet tool install --global dotnet-ef
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```
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When a new version is available, you can update with this command:
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```
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dotnet tool update dotnet-ef --global
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```
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You will now be able to use `ef` tools from the dotnet command line to interact with the database. First, we'll want to configure a connection to the database. In this sample, we'll add a method to our `AppDbContext` class, but in real-world applications this would be fetched from application configuration and passed in:
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```c#
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protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
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{
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var conn = @"Data Source=appdb.db;";
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optionsBuilder.UseSqlite(conn);
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base.OnConfiguring(optionsBuilder);
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}
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```
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### Migrations
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We can now start creating **Migrations**, blocks of code that maintain the schema of the database. Each migration is a unit that can be applied and removed programmatically from the database. Create your first migration to define the `BlogPost` storage using this command:
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```
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dotnet ef migrations add "Add BlogPosts"
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```
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This will create the `Migrations` folder and add some files to it with the definitions of the `Posts` table. Each time we modify the objects that will be stored in the database, we need to create additional migrations to be applied to the database.
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### Database Update
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We can apply any newly created migrations to our database with this command:
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```
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dotnet ef database update
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```
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You can also go the _OTHER WAY_ and create your DbContext and objects from the database using the command:
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```
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dotnet ef dbcontext scaffold "Data Source=appdb.db" Microsoft.EntityFrameworkCore.Sqlite
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```
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## CRUD Operations
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View SQL statement with
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query.ToQueryString()
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UseSqlite().LogTo()
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### Reading Data
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WithNoTracking()
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### Creating Data
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### Updating Data
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### Deleting Data
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## Relational Data
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Foreign Keys / Navigation property
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https://docs.microsoft.com/en-us/ef/core/modeling/relationships
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Many to Many
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![Many to Many relationship](img/ManyToMany.PNG)

‎sessions/0112-EfCore/SampleEntityFramework/AppDbContext.cs

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using System;
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using Microsoft.EntityFrameworkCore;
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namespace SampleEntityFramework
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{
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public class AppDbContext : DbContext {
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protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
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{
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var connString = "Data Source=appdb.db";
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optionsBuilder.UseSqlite(connString);
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// .LogTo(Console.WriteLine, Microsoft.Extensions.Logging.LogLevel.Information);
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base.OnConfiguring(optionsBuilder);
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}
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public DbSet<BlogPost> Posts { get; set; }
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public DbSet<Tag> Tags { get; set; }
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}
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}

‎sessions/0112-EfCore/SampleEntityFramework/Author.cs

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using System.Collections.Generic;
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namespace SampleEntityFramework
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{
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public class Author {
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public int Id { get; set; }
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public string Name { get; set; }
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public string TwitterUserName { get; set; }
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public IEnumerable<BlogPost> Posts { get; set; }
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}
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}

‎sessions/0112-EfCore/SampleEntityFramework/BlogPost.cs

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using System;
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using System.Collections.Generic;
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using System.Linq;
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namespace SampleEntityFramework
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{
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public class BlogPost {
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public int Id { get; set; }
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public string Title { get; set; }
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public DateTime PublishedUtc { get; set; }
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public string Content { get; set; }
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public Author Author { get; set; }
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public int? AuthorId { get; set; }
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public IList<Tag> Tags { get; set; } = new List<Tag>();
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public override string ToString() {
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var tagsText = "";
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if (Tags.Any()) tagsText = $" Tagged with: [{string.Join(',', Tags.Select(t => t.Name))}]";
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if (Author == null) return $"{Title} ({Id})" + tagsText;
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return $"{Title} ({Id}) - Written By: {Author.Name}" + tagsText;
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}
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}
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}

‎sessions/0112-EfCore/SampleEntityFramework/Migrations/20201123144404_AddBlogPost.Designer.cs

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