创建ASP.NET Core MVC应用程序(3)-基于Entity Framework Core(Code First)创建MySQL数据库表

创建数据模型类(POCO类)

在Models文件夹下添加一个User类:

namespace MyFirstApp.Models

{

    public class User

    {

        public int ID { get; set; }

        public string Name { get; set; }

        public string Email { get; set; }

        public string Bio { get; set; }

    }

}

除了你期望的用来构建Movie模型的属性外，将作为数据库主键的ID字段是必须的。

安装Entity Framework Core MySQL相关依赖项

注：其中"MySql.Data.EntityFrameworkCore": "7.0.6-ir31",要7.0.6以上版本。

Missing implementation for running EntityFramework Core code first migration。

创建Entity Framework Context数据库上下文

在Models文件夹下添加一个UserContext类:

/// <summary>

/// The entity framework context with a User DbSet

/// > dotnet ef migrations add MyMigration

/// </summary>

public class UserContext : DbContext

{

    public DbSet<User> Users { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)

    {

        var builder = new ConfigurationBuilder()

                    .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true);

        var configuration = builder.Build();

        string connectionString = configuration.GetConnectionString("MyConnection");

        optionsBuilder.UseMySQL(connectionString);

    }

    protected override void OnModelCreating(ModelBuilder builder)

    {

        // Sets the properties that make up the primary key for this entity type.

        builder.Entity<User>().HasKey(m => m.ID);

        base.OnModelCreating(builder);

    }

}

DbContext类负责连接数据库并将User对象映射到数据库记录。数据库上下文(Database Context)可以在Startup文件中的ConfigureServices方法中用依赖注入容器进行注册的：

public void ConfigureServices(IServiceCollection services)

{

    string connectionString = Configuration.GetConnectionString("MyConnection");

    services.AddDbContext<UserContext>(options =>

        options.UseMySQL(connectionString)

    );

    // Add framework services.

    services.AddMvc();

}

注：UseMySQL是MySQL.Data.EntityFrameworkCore.Extensions里面的一个扩展方法，所以要手动添加using MySQL.Data.EntityFrameworkCore.Extensions;命名空间。这个小问题也花费了我不少的时间和精力。

namespace MySQL.Data.EntityFrameworkCore.Extensions

{

  /// <summary>

  /// ContextOptionsExtensions implementations for MySQL

  /// </summary>

  public static class MySQLDbContextOptionsExtensions

    {

        public static DbContextOptionsBuilder UseMySQL(this DbContextOptionsBuilder optionsBuilder,

            string connectionString,

            Action<MySQLDbContextOptionsBuilder> MySQLOptionsAction = null)

        {

            var extension = optionsBuilder.Options.FindExtension<MySQLOptionsExtension>();

            if (extension == null)

                extension = new MySQLOptionsExtension();

            extension.ConnectionString = connectionString;

            IDbContextOptionsBuilderInfrastructure o = optionsBuilder as IDbContextOptionsBuilderInfrastructure;

            o.AddOrUpdateExtension(extension);

            MySQLOptionsAction?.Invoke(new MySQLDbContextOptionsBuilder(optionsBuilder));

            return optionsBuilder;

        }

    }

    //...

}

创建数据库

通过Migrations工具来创建数据库。

运行dotnet ef migrations add MyMigration Entity Framework .NET Core CLI Migrations命令来创建一个初始化迁移命令。

运行dotnet ef database update应用一个你所创建的新的迁移到数据库。因为你的数据库还没不存在，它会在迁移被应用之前为你创建所需的数据库。

然后就会在项目生成Migrations文件夹,包括20161121064725_MyMigration.cs文件、20161121064725_MyMigration.Designer.cs文件和UserContextModelSnapshot.cs文件：

20161121064725_MyMigration.Designer.cs类：

[DbContext(typeof(UserContext))]

[Migration("20161121064725_MyMigration")]

partial class MyMigration

{

    protected override void BuildTargetModel(ModelBuilder modelBuilder)

    {

        modelBuilder

            .HasAnnotation("ProductVersion", "1.0.0-rtm-21431");

        modelBuilder.Entity("MyFirstApp.Models.User", b =>

            {

                b.Property<int>("ID")

                    .ValueGeneratedOnAdd();

                b.Property<string>("Bio");

                b.Property<string>("Email");

                b.Property<string>("Name");

                b.HasKey("ID");

                b.ToTable("Users");

            });

    }

}

20161121064725_MyMigration.cs Partial类：

public partial class MyMigration : Migration

{

    protected override void Up(MigrationBuilder migrationBuilder)

    {

        migrationBuilder.CreateTable(

            name: "Users",

            columns: table => new

            {

                ID = table.Column<int>(nullable: false)

                    .Annotation("MySQL:AutoIncrement", true),

                Bio = table.Column<string>(nullable: true),

                Email = table.Column<string>(nullable: true),

                Name = table.Column<string>(nullable: true)

            },

            constraints: table =>

            {

                table.PrimaryKey("PK_Users", x => x.ID);

            });

    }

    protected override void Down(MigrationBuilder migrationBuilder)

    {

        migrationBuilder.DropTable(

            name: "Users");

    }

}

UserContextModelSnapshot类：

[DbContext(typeof(UserContext))]

partial class UserContextModelSnapshot : ModelSnapshot

{

    protected override void BuildModel(ModelBuilder modelBuilder)

    {

        modelBuilder

            .HasAnnotation("ProductVersion", "1.0.0-rtm-21431");

        modelBuilder.Entity("MyFirstApp.Models.User", b =>

            {

                b.Property<int>("ID")

                    .ValueGeneratedOnAdd();

                b.Property<string>("Bio");

                b.Property<string>("Email");

                b.Property<string>("Name");

                b.HasKey("ID");

                b.ToTable("Users");

            });

    }

}

新创建的数据库结构如下：

将上述的Migrations文件夹中的代码与MySQL数据库表__EFMigrationsHistory对照一下，你会发现该表是用来跟踪记录实际已经应用到数据库的迁移信息。

创建User实例并将实例保存到数据库

public class Program

{

    public static void Main(string[] args)

    {

        using (var db = new UserContext())

        {

            db.Users.Add(new User { Name = "Charlie Chu", Email = "charlie.thinker@aliyun.com", Bio = "I am Chalrie Chu." });

            var count = db.SaveChanges();

            Console.WriteLine("{0} records saved to database", count);

            Console.WriteLine();

            Console.WriteLine("All users in database:");

            foreach (var user in db.Users)

            {

                Console.WriteLine(" - {0}", user.Name);

            }

        }

    }

}

参考文档

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