EF Code First: Many-to-many and one-to-many

Question

This is probably just because my knowledge with the EF Code First fluent API is lacking, but I\'m stumped.

I want to model the following:

• A Gro

Answer 1

Based on Ladislav's excellent answer, here's how to do it without using any mappings - just attributes applied to the Model classes themselves:

public class Group 
{
    public int Id { get; set; }

    [MaxLength(300)]
    public string Name { get; set; }

    public ICollection Users { get; set; }
}

public class User
{
    public int Id { get; set; }

    [MaxLength(300)]
    public string Name { get; set; }

    [ForeignKey("PrimaryGroup")]
    public int PrimaryGroupId { get; set; }
    [Required]
    public Group PrimaryGroup { get; set; }

    [InverseProperty("Users")]
    public ICollection SecondaryGroups { get; set; }
}

Notes

If you want, you can add the virtual keyword to the 2 ICollections and the Group. This allows lazy-loading. Performance-wise, I don't recommend it, but it is possible.

I included MaxLength attributes with an arbitrary (but safe) length of 300, because putting strings out in EF without a MaxLength gets you low-performance NVarChar(MAX) columns. Totally irrelevant to what's being asked but better to post good code.

I recommend against class names "User" and "Group" for your EF classes. They're going to complicate any SQL you attempt to run later, having to type [User] and [Group] to access them, and complicate using these classes in MVC Controllers where your class User will conflict with the Context property User that gives you access to the Asp.Net Identity library.