Question

This will create two tables “Ingredient” and “Recipe” and an additional table for many-to-many mapping.

public class DC : DbContext {
    public DbSet<Ingredient> Ingredients { get; set; }
    public DbSet<Recipe> Recipes { get; set; }
}

public class Ingredient {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Recipe> Recipes { get; set; }
}

public class Recipe {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Ingredient> Ingredients { get; set; }
}

Question: I want to include additional column “quantity” in the third mapping table that will be created by Entity Framework. How to make that possible? Thanks in advance.

Answer 1

When you’ve got some extra information, I suspect it won’t really count as a mapping table any more – it’s not just a many-to-many mapping. I think you should just model it as another table:

public class Ingredient {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<RecipePart> RecipeParts { get; set; }
}

public class RecipePart {
    public int Id { get; set; }
    public Ingredient { get; set; }
    public Recipe { get; set; }
    // You'll want to think what unit this is meant to be in... another field?
    public decimal Quantity { get; set; }
}

public class Recipe {
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual ICollection<RecipePart> Parts { get; set; }
}

So now you don’t really have a many-to-many mapping – you have two ordinary many-to-one mappings. Do you definitely need to “ingredient to recipes” mapping exposed in your model at all? If you want to find out all the recipes which use a particular ingredient, you could always do a query such as:

var recipies = DB.Recipies.Where(r => r.Parts
                                       .Any(p => p.Ingredient == ingredient));