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
- HowTo: Starting with MySQL EF Core provider and Connector/Net 7.0.4
- .NET Core - New Database
- ASP.NET CORE 1.0 WITH MYSQL AND ENTITY FRAMEWORK CORE
- ASP.NET CORE 1.0 WITH SQLITE AND ENTITY FRAMEWORK 7