创建 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 MyMigrationEntity 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1121064725_MyMigration.cs文件、1121064725_MyMigration.Designer.cs文件和UserContextModelSnapshot.cs文件：

1121064725_MyMigration.Designer.cs类：

[DbContext(typeof(UserContext))][Migration("1121064725_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");});}}

1121064725_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@", 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

HowTo: Starting with MySQL EF Core provider and Connector/Net 7. Core - New CORE 1.0 WITH MYSQL AND ENTITY FRAMEWORK CORE 1.0 WITH SQLITE AND ENTITY FRAMEWORK 7

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