将项目移动到Entity Framework迁移中的项目列表

Question

I'm using Asp.Net MVC 5 with Entity Framework 6. I've got a table like this:

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

    //...rest
}

Now I want to move the Food to a list of foods. Like this:

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

    //... rest
}

If I try this and add a migration, I'll lose the data related to Food Ids. And won't know which recipe is for which food.

I tried keeping the Food and add the list like this:

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

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

    //... rest
}

But the migration adds a second foreign key and fails to update. Here's the migration code that fails:

    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");
    }

How can I move the single Food to a list of Food s without losing the current data in the table?

Answer 1

You'll need to customize your migration after creating it.

1. Modify your entity class

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

2. Use Add-Migration to scaffold the migration

3. Modify the generated migration to fill the new column with data. You'll want to fill the new Recipe_Id column in Foods with the IDs of the previously related rows.

    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"); }