aspnetcore/tutorials/first-mvc-app/adding-model/includes/adding-model3.md
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In this tutorial, classes are added for managing movies in a database. These classes are the "Model" part of the MVC app.
These model classes are used with Entity Framework Core (EF Core) to work with a database. EF Core is an object-relational mapping (ORM) framework that simplifies the data access code that you have to write.
The model classes created are known as POCO classes, from Plain Old CLR Objects. POCO classes don't have any dependency on EF Core. They only define the properties of the data to be stored in the database.
In this tutorial, model classes are created first, and EF Core creates the database.
Right-click the Models folder > Add > Class. Name the file Movie.cs.
Add a file named Movie.cs to the Models folder.
Right-click the Models folder > Add > New Class > Empty Class. Name the file Movie.cs.
Update the Movie.cs file with the following code:
The Movie class contains an Id field, which is required by the database for the primary key.
The xref:System.ComponentModel.DataAnnotations.DataType attribute on ReleaseDate specifies the type of the data (Date). With this attribute:
DataAnnotations are covered in a later tutorial.
From the Tools menu, select NuGet Package Manager > Package Manager Console (PMC).
In the PMC, run the following command:
Install-Package Microsoft.EntityFrameworkCore.SqlServer
The preceding command adds the EF Core SQL Server provider. The provider package installs the EF Core package as a dependency. Additional packages are installed automatically in the scaffolding step later in the tutorial.
From the Project menu, select Manage NuGet Packages.
In the Search field in the upper right, enter Microsoft.EntityFrameworkCore.SQLite and press the Return key to search. Select the matching NuGet package and press the Add Package button.
The Select Projects dialog will be displayed, with the MvcMovie project selected. Press the Ok button.
A License Acceptance dialog will be displayed. Review the licenses as desired, then click the Accept button.
Repeat the above steps to install the following NuGet packages:
Microsoft.VisualStudio.Web.CodeGeneration.DesignMicrosoft.EntityFrameworkCore.SqlServerMicrosoft.EntityFrameworkCore.Design<a name="dc"></a>
A database context class is needed to coordinate EF Core functionality (Create, Read, Update, Delete) for the Movie model. The database context is derived from xref:Microsoft.EntityFrameworkCore.DbContext?displayProperty=fullName and specifies the entities to include in the data model.
Create a Data folder.
Add a Data/MvcMovieContext.cs file with the following code:
The preceding code creates a DbSet<Movie> property for the entity set. In Entity Framework terminology, an entity set typically corresponds to a database table. An entity corresponds to a row in the table.
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ASP.NET Core is built with dependency injection (DI). Services (such as the EF Core DB context) must be registered with DI during application startup. Components that require these services (such as Razor Pages) are provided via constructor parameters. The constructor code that gets a DB context instance is shown later in the tutorial. In this section, you register the database context with the DI container.
Add the following using statements at the top of Startup.cs:
using MvcMovie.Data;
using Microsoft.EntityFrameworkCore;
Add the following highlighted code in Startup.ConfigureServices:
The name of the connection string is passed in to the context by calling a method on a xref:Microsoft.EntityFrameworkCore.DbContextOptions object. For local development, the ASP.NET Core configuration system reads the connection string from the appsettings.json file.
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Add a connection string to the appsettings.json file:
Build the project as a check for compiler errors.
Use the scaffolding tool to produce Create, Read, Update, and Delete (CRUD) pages for the movie model.
In Solution Explorer, right-click the Controllers folder > Add > New Scaffolded Item.
In the Add Scaffold dialog, select MVC Controller with views, using Entity Framework > Add.
Complete the Add Controller dialog:
Visual Studio creates:
Controllers/MoviesController.cs)The automatic creation of these files is known as scaffolding.
Open a command window in the project directory (The directory that contains the Program.cs, Startup.cs, and .csproj files).
On macOS and Linux, export the scaffold tool path:
export PATH=$HOME/.dotnet/tools:$PATH
Run the following command:
dotnet aspnet-codegenerator controller -name MoviesController -m Movie -dc MvcMovieContext --relativeFolderPath Controllers --useDefaultLayout --referenceScriptLibraries -sqlite
[!INCLUDE explains scaffold generated params]
Open a command window in the project directory (The directory that contains the Program.cs, Startup.cs, and .csproj files).
Run the following command:
dotnet aspnet-codegenerator controller -name MoviesController -m Movie -dc MvcMovieContext --relativeFolderPath Controllers --useDefaultLayout --referenceScriptLibraries -sqlite
[!INCLUDE explains scaffold generated params]
You can't use the scaffolded pages yet because the database doesn't exist. If you run the app and click on the Movie App link, you get a Cannot open database or no such table: Movie error message.
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Use the EF Core Migrations feature to create the database. Migrations is a set of tools that let you create and update a database to match your data model.
From the Tools menu, select NuGet Package Manager > Package Manager Console (PMC).
In the PMC, enter the following commands:
Add-Migration InitialCreate
Update-Database
Add-Migration InitialCreate: Generates a Migrations/{timestamp}_InitialCreate.cs migration file. The InitialCreate argument is the migration name. Any name can be used, but by convention, a name is selected that describes the migration. Because this is the first migration, the generated class contains code to create the database schema. The database schema is based on the model specified in the MvcMovieContext class.
Update-Database: Updates the database to the latest migration, which the previous command created. This command runs the Up method in the Migrations/{time-stamp}_InitialCreate.cs file, which creates the database.
The database update command generates the following warning:
No type was specified for the decimal column 'Price' on entity type 'Movie'. This will cause values to be silently truncated if they do not fit in the default precision and scale. Explicitly specify the SQL server column type that can accommodate all the values using 'HasColumnType()'.
You can ignore that warning, it will be fixed in a later tutorial.
[!INCLUDE more information on the PMC tools for EF Core]
[!INCLUDE more information on the CLI for EF Core]
Run the following .NET CLI commands:
dotnet ef migrations add InitialCreate
dotnet ef database update
ef migrations add InitialCreate: Generates an Migrations/{timestamp}_InitialCreate.cs migration file. The InitialCreate argument is the migration name. Any name can be used, but by convention, a name is selected that describes the migration. Because this is the first migration, the generated class contains code to create the database schema. The database schema is based on the model specified in the MvcMovieContext class (in the Data/MvcMovieContext.cs file).
ef database update: Updates the database to the latest migration, which the previous command created. This command runs the Up method in the Migrations/{time-stamp}_InitialCreate.cs file, which creates the database.
Examine the Migrations/{timestamp}_InitialCreate.cs migration file:
The Up method creates the Movie table and configures Id as the primary key. The Down method reverts the schema changes made by the Up migration.
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Run the app and click the Movie App link.
If you get an exception similar to one of the following:
SqlException: Cannot open database "MvcMovieContext-1" requested by the login. The login failed.
SqliteException: SQLite Error 1: 'no such table: Movie'.
You probably missed the migrations step.
Test the Create page. Enter and submit data.
[!NOTE] You may not be able to enter decimal commas in the
Pricefield. To support jQuery validation for non-English locales that use a comma (",") for a decimal point and for non US-English date formats, the app must be globalized. For globalization instructions, see this GitHub issue.
Test the Edit, Details, and Delete pages.
Open the Controllers/MoviesController.cs file and examine the constructor:
The constructor uses Dependency Injection to inject the database context (MvcMovieContext) into the controller. The database context is used in each of the CRUD methods in the controller.
The constructor uses Dependency Injection to inject the database context (MvcMovieContext) into the controller. The database context is used in each of the CRUD methods in the controller.
When SQLite is selected, the template generated code is ready for development. The following code shows how to inject xref:Microsoft.AspNetCore.Hosting.IWebHostEnvironment into Startup. IWebHostEnvironment is injected so ConfigureServices can use SQLite in development and SQL Server in production.
<a name="strongly-typed-models-keyword-label"></a> <a name="strongly-typed-models-and-the--keyword"></a>
Earlier in this tutorial, you saw how a controller can pass data or objects to a view using the ViewData dictionary. The ViewData dictionary is a dynamic object that provides a convenient late-bound way to pass information to a view.
MVC also provides the ability to pass strongly typed model objects to a view. This strongly typed approach enables compile time code checking. The scaffolding mechanism used this approach (that is, passing a strongly typed model) with the MoviesController class and views.
Examine the generated Details method in the Controllers/MoviesController.cs file:
The id parameter is generally passed as route data. For example https://localhost:5001/movies/details/1 sets:
movies controller (the first URL segment).details (the second URL segment).You can also pass in the id with a query string as follows:
https://localhost:5001/movies/details?id=1
The id parameter is defined as a nullable type (int?) in case an ID value isn't provided.
A lambda expression is passed in to FirstOrDefaultAsync to select movie entities that match the route data or query string value.
var movie = await _context.Movie
.FirstOrDefaultAsync(m => m.Id == id);
If a movie is found, an instance of the Movie model is passed to the Details view:
return View(movie);
Examine the contents of the Views/Movies/Details.cshtml file:
The @model statement at the top of the view file specifies the type of object that the view expects. When the movie controller was created, the following @model statement was included:
@model MvcMovie.Models.Movie
This @model directive allows access to the movie that the controller passed to the view. The Model object is strongly typed. For example, in the Details.cshtml view, the code passes each movie field to the DisplayNameFor and DisplayFor HTML Helpers with the strongly typed Model object. The Create and Edit methods and views also pass a Movie model object.
Examine the Index.cshtml view and the Index method in the Movies controller. Notice how the code creates a List object when it calls the View method. The code passes this Movies list from the Index action method to the view:
When the movies controller was created, scaffolding included the following @model statement at the top of the Index.cshtml file:
The @model directive allows you to access the list of movies that the controller passed to the view by using a Model object that's strongly typed. For example, in the Index.cshtml view, the code loops through the movies with a foreach statement over the strongly typed Model object:
Because the Model object is strongly typed (as an IEnumerable<Movie> object), each item in the loop is typed as Movie. Among other benefits, this means that you get compile time checking of the code.
[!div class="step-by-step"] Previous Adding a View Next Working with SQL
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