EntityFrameworkCore 根据实体类自动创建数据库

1.首先新建 Asp.Net Core WebApi 项目

2.添加一下引用：

2.1 Pomelo.EntityFrameworkCore.MySql（我用的Mysql 根据自己情况引用就行）

2.2 Microsoft.EntityFrameworkCore

2.3 Microsoft.EntityFrameworkCore.Design

3.使项目支持dotnet ef 工具以使用Migrations

3.1 手动修改csproj文件(手动添加是因为在nuget添加Microsoft.EntityFrameworkCore.Tools.DotNet 时报错，估计是vs的问题)，添加一下配置

<ItemGroup>
<DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" />
</ItemGroup>

4.打开CMD命令 cd到项目目录下(C:\Users\Administrator\source\repos\CodeFirst\CodeFirst),执行

dotnet build

Microsoft (R) Build Engine version 15.1.545.13942 Copyright (C) Microsoft Corporation. All rights reserved. Startup.cs(45,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [C:\WorkSpacesC\DotNetCore\EntityFrameworkCoreMigrationsDemo\EntityFrameworkCoreMigrationsDemo\EntityFrameworkCoreMigrationsDemo.csproj] EntityFrameworkCoreMigrationsDemo -> C:\WorkSpacesC\DotNetCore\EntityFrameworkCoreMigrationsDemo\EntityFrameworkCoreMigrationsDemo\bin\Debug\netcoreapp1.0\EntityFrameworkCoreMigrationsDemo.dll Build succeeded. Startup.cs(45,13): warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call. [C:\WorkSpacesC\DotNetCore\EntityFrameworkCoreMigrationsDemo\EntityFrameworkCoreMigrationsDemo\EntityFrameworkCoreMigrationsDemo.csproj] 1 Warning(s) 0 Error(s) Time Elapsed 00:00:04.76

5. 第4步完成后继续执行

 dotnet ef

可以看见独角兽就说明引用成功了。距离胜利更近一步了

6.创建实例 StudentDbContext和相关实体类

using CodeFirst.Model.Entity;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodeFirst.Model.Db
{
  public class StudentDbContext: DbContext
    {
        public StudentDbContext(DbContextOptions<StudentDbContext> options)
            : base(options)
        {
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseMySql(
                @"Server=localhost;Port=3306;Database=Policy;UId=root;Pwd=mysql.com");
        }

        public DbSet<Student> Student { get; set; }
        public DbSet<Teacher> Teacher { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Text;

namespace CodeFirst.Model.Entity
{
   public class Student
    {
        [Key]
        public int Id { get; set; }
        public string Name { get; set; }
        public Teacher Teach { get; set; }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace CodeFirst.Model.Entity
{
   public class Teacher
    {
        public int Id { get; set; }
        public int Age { get; set; }
        public List<Student> Stus { get; set; }
    }
}

7. 在Startup将StudentDbContext 注册为服务

8.使用Migrations 新建数据库初始化类DbInitializer

using CodeFirst.Model.Db;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;

namespace CodeFirst.Model
{
   public class DbInitializer
    {
        public void InitializeAsync(StudentDbContext context)
        {
            //var migrations = await context.Database.GetPendingMigrationsAsync();//获取未应用的Migrations，不必要，MigrateAsync方法会自动处理
             context.Database.MigrateAsync();//根据Migrations修改/创建数据库
        }
    }
}

9.在Startup.cs的Configure方法中，添加参数StudentContext context，netcore会使用DI将DbContext注入到Configure方法，并添加对DbInitializer的调用。

10.使用dotnet ef命令创建Migrations：dotnet ef migrations add text text随便起名

C:\Users\Administrator\source\repos\CodeFirst\CodeFirst>dotnet ef migrations add Initial

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:02.32
Done. To undo this action, use 'ef migrations remove'

如果执行dotnet ef migrations add Initial报错 :