创建ASP.NETCoreMVC应用程序(3)-基于EntityFrameworkCore(CodeFirst)创建MySQL数据库 ...

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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)
    {
        builder.Entity<User>().HasKey(m => m.ID);
        base.OnModelCreating(builder);
    }
}

OnConfiguring方法里面的指定使用MySQL provider及具体的连接字符串等逻辑也可以统一放到Startup类中的ConfigureServices方法中：

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。

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 = "[email protected]", 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);
            }
        }
    }
}