How I can achieve two different foreign keys in Entity Framework?

Question

I need to bind some relations in Entity Framework Code First but I don't know how to. I searched deeply, I tried a lot of ways but still without luck. I think I need to use the fluent API.

Scenario

Organizations has many Notes . Projects has many Notes . Notes has one Organization or Project .

The idea is to bind every entity ( Organization or Project ) to only one column in Note entity: SourceKey .

Organization

public class Organization
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid ID { get; set; }

    [Required(ErrorMessage = "A name is required.")]
    public string Name { get; set; }

    public virtual ICollection<Project> Projects { get; set; }
    public virtual ICollection<Note> Notes { get; set; }
}

Project

public class Project
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid ID { get; set; }

    [Required(ErrorMessage = "An organization is required.")]
    [Display(Name = "Organization")]
    public Guid OrganizationID { get; set; }

    [Required(ErrorMessage = "A name is required.")]
    public string Name { get; set; }

    public virtual Organization Organization { get; set; }
    public virtual ICollection<Note> Notes { get; set; }
}

Note

public class Note
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid ID { get; set; }

    public Guid SourceKey { get; set; }

    [Required(ErrorMessage = "A title is required.")]
    public string Title { get; set; }

    [Column(TypeName = "ntext")]
    public string Value { get; set; }

    public string Tags { get; set; }
}

So an example of data can be:

Organizations

7846ac27-d490-4483-8f0b-975a11333dea, Google

Projects

3446ac27-d490-4323-8121-921a11333dac, Search
7846ac27-8497-5683-213b-933a11233abc, Maps

Notes

1236ac27-d490-4323-8121-921a11333dac, 7846ac27-d490-4483-8f0b-975a11333dea, A note for Google organization
2346ac27-d490-4323-8121-921a11335aab, 7846ac27-d490-4483-8f0b-975a11333dea, Another note for Google organization
3456ac27-d490-4323-8121-921a11331bcc, 7846ac27-8497-5683-213b-933a11233abc, Just a note for Maps project

BTW

I don't need to navigate from Notes (up) to Organization or Project. If I have an Organization or Project, I will need to navigate (down) to Notes.

Answer 1

As mentioned above, if you don't require navigation properties from notes, you can omit them.

If you then included two fields on the Note class to use for foreign key associations:

public class Note
{
    // Code

    public Guid OrganizationId { get; set; }
    public Guid ProjectId { get; set; }
}

I assume most notes won't belong to both an Organisation , and a Project (although they can).

You should be able to configure your mapping using the fluent API like this:

modelBuilder.Entity<Organization>()
        .HasMany(o => o.Notes)                    // Many Notes
        .WithOptional()                           // No navigation property on Notes            
        .HasForeignKey(n => n.OrganizationId );   // Use OrganizationId as a foreign key

modelBuilder.Entity<Project>()
        .HasMany(o => o.Notes)
        .WithOptional()
        .HasForeignKey(n => n.ProjectId);

Answer 2

You can define the Note entity without navigation properties,

public class Note
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid ID { get; set; }

    public Guid SourceKey { get; set; }

    [Required(ErrorMessage = "A title is required.")]
    public string Title { get; set; }

    [Column(TypeName = "ntext")]
    public string Value { get; set; }

    public string Tags { get; set; }

    public int OrganizationId { get; set; }
    public int ProjectId { get; set; }
}

Answer 3

If you don't need navigation properties, you can define it simply using the class below:

public class Note
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid NoteID { get; set; }

    public Guid SourceKey { get; set; }

    [Required(ErrorMessage = "A title is required.")]
    public string Title { get; set; }

    [Column(TypeName = "ntext")]
    public string Value { get; set; }

    public string Tags { get; set; }

    public Guid OrganizationId { get; set; }
    public Guid ProjectId { get; set; }

}

Note OrganizationId and ProjectId are of type Guid .

Answer 4

I think that the use of one column (SourceKey) for multiple foreign keys is not possible. It throws you an error. I was pretty sure that was possible but maybe I'm confused with the MyISAM tables in MySQL. I will use the foreign keys columns in the Note model as Chris suggest. Thanks to everybody.