Part 4, add a model to an ASP.NET Core MVC app

By Rick Anderson and Jon P Smith.

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.

Add a data model class

Visual Studio

Right-click the Models folder > Add > Class. Name the file Movie.cs.

Visual Studio Code

Add a file named Movie.cs to the Models folder.

Update the Models/Movie.cs file with the following code:

using System.ComponentModel.DataAnnotations;

namespace MvcMovie.Models;

public class Movie
{
    public int Id { get; set; }
    public string? Title { get; set; }
    [DataType(DataType.Date)]
    public DateTime ReleaseDate { get; set; }
    public string? Genre { get; set; }
    public decimal Price { get; set; }
}

The Movie class contains an Id field, which is required by the database for the primary key.

The DataType attribute on ReleaseDate specifies the type of the data (Date). With this attribute:

• The user isn't required to enter time information in the date field.
• Only the date is displayed, not time information.

DataAnnotations are covered in a later tutorial.

The question mark after string indicates that the property is nullable. For more information, see Nullable reference types.

Add NuGet packages

Visual Studio

Visual Studio automatically installs the required packages.

Build the project as a check for compiler errors.

Visual Studio Code

Run the following .NET CLI commands:

dotnet tool uninstall --global dotnet-aspnet-codegenerator
dotnet tool install --global dotnet-aspnet-codegenerator
dotnet tool uninstall --global dotnet-ef
dotnet tool install --global dotnet-ef
dotnet add package Microsoft.EntityFrameworkCore.Design
dotnet add package Microsoft.EntityFrameworkCore.SQLite
dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.SqlServer
dotnet add package Microsoft.EntityFrameworkCore.Tools

The preceding commands add:

• The command-line interface (CLI) tools for EF Core
• The aspnet-codegenerator scaffolding tool.
• Design time tools for EF Core
• The EF Core SQLite provider, which installs the EF Core package as a dependency.
• Packages needed for scaffolding: Microsoft.VisualStudio.Web.CodeGeneration.Design and Microsoft.EntityFrameworkCore.SqlServer.

For guidance on multiple environment configuration that permits an app to configure its database contexts by environment, see Use multiple environments in ASP.NET Core.

Note

By default the architecture of the .NET binaries to install represents the currently running OS architecture. To specify a different OS architecture, see dotnet tool install, --arch option. For more information, see GitHub issue dotnet/AspNetCore.Docs #29262.

In Visual Studio Code, press Ctrl+F5 (Windows) or ⌘+F5 (macOS) to run the app without debugging.

In the Panel below the editor region, select the PROBLEMS tab, or from the View menu, select Problems if it is not currently in view. Verify there are no compilation errors.

Scaffold movie pages

Use the scaffolding tool to produce Create, Read, Update, and Delete (CRUD) pages for the movie model.

Visual Studio

In Solution Explorer, right-click the Controllers folder and select Add > New Scaffolded Item.

In the Add New Scaffolded Item dialog:

• In the left pane, select Installed > Common > MVC.
• Select MVC Controller with views, using Entity Framework.
• Select Add.

Complete the Add MVC Controller with views, using Entity Framework dialog:

• In the Model class drop down, select Movie (MvcMovie.Models).
• In the Data context class row, select the + (plus) sign.
  • In the Add Data Context dialog, the class name MvcMovie.Data.MvcMovieContext is generated.
  • Select Add.
• In the Database provider drop down, select SQL Server.
• Views and Controller name: Keep the default.
• Select Add.

If you get an error message, select Add a second time to try it again.

Scaffolding adds the following packages:

• Microsoft.EntityFrameworkCore.SqlServer
• Microsoft.EntityFrameworkCore.Tools
• Microsoft.VisualStudio.Web.CodeGeneration.Design

Scaffolding creates the following:

• A movies controller: Controllers/MoviesController.cs
• Razor view files for Create, Delete, Details, Edit, and Index pages: Views/Movies/*.cshtml
• A database context class: Data/MvcMovieContext.cs

Scaffolding updates the following:

• Inserts required package references in the MvcMovie.csproj project file.
• Registers the database context in the Program.cs file.
• Adds a database connection string to the appsettings.json file.

The automatic creation of these files and file updates is known as scaffolding.

The scaffolded pages can't be used yet because the database doesn't exist. Running the app and selecting the Movie App link results in a Cannot open database or no such table: Movie error message.

Build the app to verify that there are no errors.

Visual Studio Code

Open a command window in the project directory. The project directory is the directory that contains the Program.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 MvcMovie.Data.MvcMovieContext --relativeFolderPath Controllers --useDefaultLayout --referenceScriptLibraries --databaseProvider sqlite

The following table details the ASP.NET Core code generator parameters:

Parameter	Description
-m	The name of the model.
-dc	The data context.
--relativeFolderPath	The relative output folder path to create the files.
--useDefaultLayout|-udl	The default layout should be used for the views.
--referenceScriptLibraries	Adds _ValidationScriptsPartial to Edit and Create pages.
--databaseProvider sqlite	Specify DbContext should use SQLite instead of SQL Server.

Use the h switch to get help on the aspnet-codegenerator controller command:

dotnet aspnet-codegenerator controller -h

For more information, see dotnet aspnet-codegenerator

Scaffolding creates the following:

• A movies controller: Controllers/MoviesController.cs
• Razor view files for Create, Delete, Details, Edit, and Index pages: Views/Movies/*.cshtml
• A database context class: Data/MvcMovieContext.cs

Scaffolding updates the following:

• Registers the database context in the Program.cs file
• Adds a database connection string to the appsettings.json file.

The automatic creation of these files and file updates is known as scaffolding.

The scaffolded pages can't be used yet because the database doesn't exist. Running the app and selecting the Movie App link results in a Cannot open database or no such table: Movie error message.

Build the app to verify that there are no errors.

Use SQLite for development, SQL Server for production

The following highlighted code in Program.cs shows how to use SQLite in development and SQL Server in production.

var builder = WebApplication.CreateBuilder(args);

if (builder.Environment.IsDevelopment())
{
    builder.Services.AddDbContext<MvcMovieContext>(options =>
        options.UseSqlite(builder.Configuration.GetConnectionString("MvcMovieContext")));
}
else
{
    builder.Services.AddDbContext<MvcMovieContext>(options =>
        options.UseSqlServer(builder.Configuration.GetConnectionString("ProductionMvcMovieContext")));
}

Initial migration

Use the EF Core Migrations feature to create the database. Migrations is a set of tools that create and update a database to match the data model.

Visual Studio

From the Tools menu, select NuGet Package Manager > Package Manager Console .

In the Package Manager Console (PMC), enter the following command:

Add-Migration InitialCreate

• 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.

The following warning is displayed, which is addressed in a later step:

No store type was specified for the decimal property '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 in 'OnModelCreating' using 'HasColumnType', specify precision and scale using 'HasPrecision', or configure a value converter using 'HasConversion'.

In the PMC, enter the following command:

Update-Database

• 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.

For more information on the PMC tools for EF Core, see EF Core tools reference - PMC in Visual Studio.

Visual Studio Code

Run the following .NET CLI command:

dotnet ef migrations add InitialCreate

• ef migrations add 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. This is the first migration, so 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.

The following warning is displayed, which is addressed in a later step:

No store type was specified for the decimal property '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 in 'OnModelCreating' using 'HasColumnType', specify precision and scale using 'HasPrecision', or configure a value converter using 'HasConversion'.

Run the following .NET CLI command:

dotnet ef database update

• 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.

For more information on maintaining multiple providers such as Microsoft SQL Server and SQLite, see Migrations with Multiple Providers.

Test the app

Visual Studio

Run the app and select the Movie App link.

If you get an exception similar to the following, you may have missed the Update-Database command in the migrations step:

SqlException: Cannot open database "MvcMovieContext-1" requested by the login. The login failed.

Visual Studio Code

Run the app and select the Movie App link.

If you get an exception similar to the following, you may have missed the dotnet ef database update command in the migrations step:

SqliteException: SQLite Error 1: 'no such table: Movie'.

Note

You may not be able to enter decimal commas in the Price field. 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.

Examine the generated database context class and registration

With EF Core, data access is performed using a model. A model is made up of entity classes and a context object that represents a session with the database. The context object allows querying and saving data. The database context is derived from Microsoft.EntityFrameworkCore.DbContext and specifies the entities to include in the data model.

Scaffolding creates the Data/MvcMovieContext.cs database context class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using MvcMovie.Models;

namespace MvcMovie.Data
{
    public class MvcMovieContext : DbContext
    {
        public MvcMovieContext (DbContextOptions<MvcMovieContext> options)
            : base(options)
        {
        }

        public DbSet<MvcMovie.Models.Movie> Movie { get; set; } = default!;
    }
}

The preceding code creates a DbSet<Movie> property that represents the movies in the database.

Dependency injection

ASP.NET Core is built with dependency injection (DI). Services, such as the database context, are registered with DI in Program.cs. These services are provided to components that require them via constructor parameters.

In the Controllers/MoviesController.cs file, the constructor uses Dependency Injection to inject the MvcMovieContext database context into the controller. The database context is used in each of the CRUD methods in the controller.

Scaffolding generated the following highlighted code in Program.cs:

Visual Studio

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("MvcMovieContext") ?? throw new InvalidOperationException("Connection string 'MvcMovieContext' not found.")));

Visual Studio Code

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddDbContext<MvcMovieContext>(options =>
    options.UseSqlite(builder.Configuration.GetConnectionString("MvcMovieContext")));

The ASP.NET Core configuration system reads the "MvcMovieContext" database connection string.

Examine the generated database connection string

Scaffolding added a connection string to the appsettings.json file:

Visual Studio

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "MvcMovieContext": "Server=(localdb)\\mssqllocaldb;Database=MvcMovieContext-4ebefa10-de29-4dea-b2ad-8a8dc6bcf374;Trusted_Connection=True;MultipleActiveResultSets=true"
  }
}

Visual Studio Code

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "ConnectionStrings": {
    "MvcMovieContext": "Data Source=MvcMovie.db"
  }
}

For local development, the ASP.NET Core configuration system reads the ConnectionString key from the appsettings.json file.

The InitialCreate class

Examine the Migrations/{timestamp}_InitialCreate.cs migration file:

using System;
using Microsoft.EntityFrameworkCore.Migrations;

#nullable disable

namespace MvcMovie.Migrations
{
    /// <inheritdoc />
    public partial class InitialCreate : Migration
    {
        /// <inheritdoc />
        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.CreateTable(
                name: "Movie",
                columns: table => new
                {
                    Id = table.Column<int>(type: "int", nullable: false)
                        .Annotation("SqlServer:Identity", "1, 1"),
                    Title = table.Column<string>(type: "nvarchar(max)", nullable: true),
                    ReleaseDate = table.Column<DateTime>(type: "datetime2", nullable: false),
                    Genre = table.Column<string>(type: "nvarchar(max)", nullable: true),
                    Price = table.Column<decimal>(type: "decimal(18,2)", nullable: false)
                },
                constraints: table =>
                {
                    table.PrimaryKey("PK_Movie", x => x.Id);
                });
        }

        /// <inheritdoc />
        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.DropTable(
                name: "Movie");
        }
    }
}

In the preceding code:

• InitialCreate.Up creates the Movie table and configures Id as the primary key.
• InitialCreate.Down reverts the schema changes made by the Up migration.

Dependency injection in the controller

Open the Controllers/MoviesController.cs file and examine the constructor:

public class MoviesController : Controller
{
    private readonly MvcMovieContext _context;

    public MoviesController(MvcMovieContext context)
    {
        _context = context;
    }

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.

Test the Create page. Enter and submit data.

Test the Edit, Details, and Delete pages.

Strongly typed models and the @model directive

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 provides the ability to pass strongly typed model objects to a view. This strongly typed approach enables compile time code checking. The scaffolding mechanism passed a strongly typed model in the MoviesController class and views.

Examine the generated Details method in the Controllers/MoviesController.cs file:

// GET: Movies/Details/5
public async Task<IActionResult> Details(int? id)
{
    if (id == null)
    {
        return NotFound();
    }

    var movie = await _context.Movie
        .FirstOrDefaultAsync(m => m.Id == id);
    if (movie == null)
    {
        return NotFound();
    }

    return View(movie);
}

The id parameter is generally passed as route data. For example, https://localhost:5001/movies/details/1 sets:

• The controller to the movies controller, the first URL segment.
• The action to details, the second URL segment.
• The id to 1, the last URL segment.

The id can be passed in with a query string, as in the following example:

https://localhost:5001/movies/details?id=1

The id parameter is defined as a nullable type (int?) in cases when the id value isn't provided.

A lambda expression is passed in to the FirstOrDefaultAsync method 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:

@model MvcMovie.Models.Movie

@{
    ViewData["Title"] = "Details";
}

<h1>Details</h1>

<div>
    <h4>Movie</h4>
    <hr />
    <dl class="row">
        <dt class = "col-sm-2">
            @Html.DisplayNameFor(model => model.Title)
        </dt>
        <dd class = "col-sm-10">
            @Html.DisplayFor(model => model.Title)
        </dd>
        <dt class = "col-sm-2">
            @Html.DisplayNameFor(model => model.ReleaseDate)
        </dt>
        <dd class = "col-sm-10">
            @Html.DisplayFor(model => model.ReleaseDate)
        </dd>
        <dt class = "col-sm-2">
            @Html.DisplayNameFor(model => model.Genre)
        </dt>
        <dd class = "col-sm-10">
            @Html.DisplayFor(model => model.Genre)
        </dd>
        <dt class = "col-sm-2">
            @Html.DisplayNameFor(model => model.Price)
        </dt>
        <dd class = "col-sm-10">
            @Html.DisplayFor(model => model.Price)
        </dd>
    </dl>
</div>
<div>
    <a asp-action="Edit" asp-route-id="@Model.Id">Edit</a> |
    <a asp-action="Index">Back to List</a>
</div>

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:

// GET: Movies
public async Task<IActionResult> Index()
{
    return View(await _context.Movie.ToListAsync());
}

The code returns problem details if the Movie property of the data context is null.

When the movies controller was created, scaffolding included the following @model statement at the top of the Index.cshtml file:

@model IEnumerable<MvcMovie.Models.Movie>

The @model directive allows access to 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:

@model IEnumerable<MvcMovie.Models.Movie>

@{
    ViewData["Title"] = "Index";
}

<h1>Index</h1>

<p>
    <a asp-action="Create">Create New</a>
</p>
<table class="table">
    <thead>
        <tr>
            <th>
                @Html.DisplayNameFor(model => model.Title)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.ReleaseDate)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.Genre)
            </th>
            <th>
                @Html.DisplayNameFor(model => model.Price)
            </th>
            <th></th>
        </tr>
    </thead>
    <tbody>
@foreach (var item in Model) {
        <tr>
            <td>
                @Html.DisplayFor(modelItem => item.Title)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.ReleaseDate)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.Genre)
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.Price)
            </td>
            <td>
                <a asp-action="Edit" asp-route-id="@item.Id">Edit</a> |
                <a asp-action="Details" asp-route-id="@item.Id">Details</a> |
                <a asp-action="Delete" asp-route-id="@item.Id">Delete</a>
            </td>
        </tr>
}
    </tbody>
</table>

Because the Model object is strongly typed as an IEnumerable<Movie> object, each item in the loop is typed as Movie. Among other benefits, the compiler validates the types used in the code.

Additional resources

• Entity Framework Core for Beginners
• Tag Helpers
• Globalization and localization

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