Question

我正在使用带有Entity Framework 6的Asp.Net MVC 5.我有一个这样的表：

public class Recipe
{
    [Required]
    public virtual Food Food { get; set; }

    //...rest
}

现在我想将Food移到食物清单中。像这样：

public class Recipe
{
    public virtual IList<Food> Foods { get; set; }

    //... rest
}

如果我尝试这个并添加迁移，我将丢失与Food ID相关的数据。并且不知道哪种食谱适合哪种食物。

我尝试保留Food并添加如下列表：

public class Recipe
{
    [Required]
    public virtual Food Food { get; set; }

    public virtual IList<Food> Foods { get; set; }

    //... rest
}

但是迁移添加了第二个外键并且无法更新。这是失败的迁移代码：

    public override void Up()
    {
        DropForeignKey("dbo.Recipes", "Food_ID", "dbo.Foods");
        DropIndex("dbo.Recipes", new[] { "Food_ID" });
        AddColumn("dbo.Foods", "Recipe_Id", c => c.Int());
        AddColumn("dbo.Foods", "Recipe_Id1", c => c.Int());
        AlterColumn("dbo.Recipes", "Food_ID", c => c.Int());
        CreateIndex("dbo.Foods", "Recipe_Id");
        CreateIndex("dbo.Foods", "Recipe_Id1");
        CreateIndex("dbo.Recipes", "Food_ID");
        AddForeignKey("dbo.Foods", "Recipe_Id", "dbo.Recipes", "Id");
        AddForeignKey("dbo.Foods", "Recipe_Id1", "dbo.Recipes", "Id");
        AddForeignKey("dbo.Recipes", "Food_ID", "dbo.Foods", "ID");
    }

如何在不丢失表格中的当前数据的情况下将单个Food移至Food列表？

Answer 1

创建后，您需要自定义迁移。

修改您的实体类

public class Recipe
{
    public virtual IList<Food> Foods { get; set; }

    //... rest
}

使用Add-Migration来构建迁移

修改生成的迁移以使用数据填充新列。您需要使用以前相关行的ID填充Recipe_Id中的新Foods列。

public override void Up()
{
    DropForeignKey("dbo.Recipes", "Food_ID", "dbo.Foods");
    DropIndex("dbo.Recipes", new[] { "Food_ID" });
    AddColumn("dbo.Foods", "Recipe_Id", c => c.Int());

    // Update values from existing data, not sure if the syntax is perfect
    Sql(@"UPDATE dbo.Foods SET Recipe_Id = r.Id
          FROM (SELECT Id, Food_ID FROM dbo.Recipes) AS r
          WHERE Foods.ID = r.Food_ID");

    DropColumn("dbo.Recipes", "Food_ID");
    CreateIndex("dbo.Foods", "Recipe_Id");
    AddForeignKey("dbo.Foods", "Recipe_Id", "dbo.Recipes", "Id");
}

将项目移动到Entity Framework迁移中的项目列表

1 个答案: