如何在__MigrationHistory表中添加其他列?

时间:2014-06-03 21:17:28

标签: c# entity-framework-6 ef-migrations

根据Customizing the Migrations History Table,我应该能够添加一列,但是我无法找到有关如何实际添加新列的任何示例。

我很担心放置实际属性的位置以及如何将其配置到现有的__MigrationHistory表。从文档中,我可以自定义表配置..

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    base.OnModelCreating(modelBuilder);
    modelBuilder.Entity<HistoryRow>().ToTable(tableName: "MigrationHistory", schemaName: "admin");
    modelBuilder.Entity<HistoryRow>().Property(p => p.MigrationId).HasColumnName("Migration_ID");
}

...但我无法修改HistoryRow实体。

我是否应该根据HistoryRow实体添加新的派生类型?

1 个答案:

答案 0 :(得分:7)

首先,您需要为历史记录行实体创建一个新类。例如:

public sealed class MyHistoryRow : HistoryRow
{
    //We will just add a text column
    public string MyColumn { get; set; }
}

接下来我们需要一个上下文,就像我们对普通EF操作一样,但这次我们继承自HistoryContext

public class MyHistoryContext : HistoryContext
{
    //We have to 'new' this as we are overriding the DbSet type
    public new DbSet<MyHistoryRow> History { get; set; }

    public MyHistoryContext(DbConnection dbConnection, string defaultSchema)
        : base(dbConnection, defaultSchema)
    {
    }

    //This part isn't needed but shows what you can do
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        //Rename the table and put it in a different schema. Our new table
        //will be called 'admin.MigrationHistory'
        modelBuilder.Entity<MyHistoryRow>().ToTable(tableName: "MigrationHistory", schemaName: "admin");

        //Rename one of the columns for fun
        modelBuilder.Entity<MyHistoryRow>().Property(p => p.MigrationId).HasColumnName("Migration_ID");
    }
} 

现在要连接它们,我们需要配置它,所以首先我们设置配置:

public class MyConfiguration : DbConfiguration
{
    public MyConfiguration()
    {
        //Set our new history context to be the one that gets used
        this.SetHistoryContext("System.Data.SqlClient",
            (connection, defaultSchema) => new MyHistoryContext(connection, defaultSchema)); 
    }
}

最后,通过修改我们的web.config来使配置适用:(你必须填写你自己的命名空间和应用程序集:

<entityFramework codeConfigurationType="Namespace.MyConfiguration, ApplicationAssembly">
    ...snipped...
</entityFramework>

执行此操作的副作用是,如果/当您启用迁移时,您需要明确说明您正在使用的上下文。这显然是因为你现在在程序集中有两种上下文类型(除非你将它们拆分出来。)所以你现在需要运行这样的命令:

enable-migrations -ContextTypeName Namespace.YourContextClass