EF Code First Migrations数据库迁移

1、EF Code First创建数据库

步骤1：新建控制台应用程序

步骤2：安装EntityFramework

在程序包管理器控制台中执行以下语句：

PM>Install-Package EntityFramework

2、项目结构

两个实体及映射，PortalContext代码如下：

using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Portal.Enities;
using Portal.Mapping;

namespace Portal
{
    public class PortalContext : DbContext
    {
        static PortalContext()
        {
            System.Data.Entity.Database.SetInitializer<PortalContext>(null);

           //Database.SetInitializer(new DropCreateDatabaseAlways<PortalContext>());
        }

        public DbSet<Category> Categories { get; set; }
        public DbSet<Province> Provinces { get; set; }


        /// <summary>
        /// This method is called when the model for a derived context has been initialized, but
        /// before the model has been locked down and used to initialize the context.  The default
        /// implementation of this method does nothing, but it can be overridden in a derived class
        /// such that the model can be further configured before it is locked down.
        /// </summary>
        /// <remarks>
        /// Typically, this method is called only once when the first instance of a derived context
        /// is created.  The model for that context is then cached and is for all further instances of
        /// the context in the app domain.  This caching can be disabled by setting the ModelCaching
        /// property on the given ModelBuidler, but note that this can seriously degrade performance.
        /// More control over caching is provided through use of the DbModelBuilder and DbContextFactory
        /// classes directly.
        /// </remarks>
        /// <param name="modelBuilder"> The builder that defines the model for the context being created. </param>
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.Add(new CategoryMap());
            modelBuilder.Configurations.Add(new ProvinceMap());
        }

    }
}

其他代码，可以从本博文最后下载。

3、EF Code First数据库迁移

步骤1：生成数据库

修改PortailContext.cs的静态构造函数，取消当数据库模型发生改变时删除当前数据库重建数据库的设置。

static PortalContext()
        {
            System.Data.Entity.Database.SetInitializer<PortalContext>(null);

            //Database.SetInitializer(new DropCreateDatabaseAlways<PortalContext>());
        }

步骤2：在程序包管理器控制台，执行以下语句

PM>Enable-Migrations –EnableAutomaticMigrations

运行结果如下：

Configuration代码如下

namespace Portal.Migrations
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Migrations;
    using System.Linq;

    internal sealed class Configuration : DbMigrationsConfiguration<Portal.PortalContext>
    {
        public Configuration()
        {
            AutomaticMigrationsEnabled = true;
        }

        protected override void Seed(Portal.PortalContext context)
        {
            //  This method will be called after migrating to the latest version.

            //  You can use the DbSet<T>.AddOrUpdate() helper extension method 
            //  to avoid creating duplicate seed data. E.g.
            //
            //    context.People.AddOrUpdate(
            //      p => p.FullName,
            //      new Person { FullName = "Andrew Peters" },
            //      new Person { FullName = "Brice Lambson" },
            //      new Person { FullName = "Rowan Miller" }
            //    );
            //
        }
    }
}

步骤3：在程序包管理器控制台执行以下语句

PM>Add-Migration InitialCreate

运行结果如下：

步骤4：在程序包管理器控制台执行以下语句

PM>Update-Database –Verbose

执行结果如下：

到此，数据完成了创建：

4、EF Code First添加实体

步骤1：增加City.cs实体

步骤2：在程序包管理器控制台执行以下语句：

PM>Add-Migration AddCity

执行结果如下：

步骤3：更新实体到数据库，在程序包管理器控制台执行以下语句

PM>Update-Database –Verbose

数据库变化如下：

5、EF Code First修改实体

步骤1：修改City，增加CityNo属性

步骤2：在程序包管理器控制台中执行以下代码：

PM>Add-Migration UpdateCity

执行结果如下：

步骤3：在程序包管理器控制台执行以下语句

PM>Update-Database –Verbose

执行结果如下：

6、版本回溯

步骤1：修改数据库中的City，删除CityNo字段

步骤2：在程序包管理器控制器执行以下语句：

PM>Add-Migration ModifyCity

步骤3：更新到数据库，在程序包管理器控制台执行以下语句：

PM>Update-Database –Verbose

在程序包管理器控制台执行以下语句：

PM>Update-Database –SourceMigration “201701091349455_AddCity.cs”

执行结果如下：

7、其他命令

1、为指定的DbContext启用数据库迁移

PM> Enable-Migrations -ContextTypeName Portal.PortalContext

2、设置是否允许自动迁移

Enable-Migrations

生成的Configuration.cs类文件的构造函数

public Configuration()
{
      AutomaticMigrationsEnabled = false;
}

3、Enable-Migrations指定项目名称

PM>Enable-Migrations -StartUpProjectName Portal

如果在“Package Manager Console”中选择了默认项目可以不设置“-StartUpProjectName”参数；如果多次执行此命令可以添加-Force参数。

4、查看所执行的Sql语句 -Verbose指令

Update-Database -Verbose 

8、示例下载

Portal示例下载：https://files.cnblogs.com/files/zsy/Portal.rar