如何在EF Core中将两个类映射到一个表

Question

public class User
{
    public Account Account { get; set; }
    public string SomeInfo { get; set; }
    public Guid Id { get; set; }
}

public class Account
{
    public string Name { get; set; }
}

public class UserEntityTypeConfiguration : IEntityTypeConfiguration<User>
{
    public virtual void Configure(EntityTypeBuilder<User> builder)
    {
        builder.HasKey(x => x.Id);
        builder
            .Property(t => t.Id)
            .ValueGeneratedOnAdd();
    }
}

Can I map to a single table that looks like this?

| Id | SomeInfo | AccountName |
-------------------------------
| 1  | info1    | name1       |
| 2  | info2    | NULL        |

And after the mapping, 1 would map to:

User.SomeInfo        is "info1"
User.Account         is not null
User.Account.Name    is "name1"

and loading 2 would result in

User.SomeInfo        is "info2"
User.Account         is null

Can anyone help?

Answer 1

What you want cannot be done exactly the way you want - when using table splitting/owned entities that reside in the same table as the owner, it looks like EFCore requires the related entity not be null.

I figure there are two options - shared primary key (which would required two tables and an eager/explicit load to load the dependent entity with the principal) or Table-per-Hierarchy (TPH) inheritance (which would require two entity types).

Shared Primary Key:

public class SharedKeyPrincipal
{
    public int Id { get; set; }
    public int PrincipalProperty { get; set; }
    public SharedKeyDependent Dependent { get; set; }
}
public class SharedKeyDependent
{
    public int Id { get; set; }
    public int DependentProperty { get; set; }
    public SharedKeyPrincipal Principal { get; set; }
}

modelBuilder.Entity<SharedKeyDependent>()
    .HasOne( d => d.Principal )
    .WithOne( p => p.Dependent )
    .IsRequired()
    .HasForeignKey<SharedKeyDependent>( d => d.Id );

var principals = dbContext.Set<SharedKeyPrincipal>()
    .Include( p => p.Dependent )
    .ToArray();

TPH:

public class InheritanceBaseEntity
{
    public int Id { get; set; }
    public int BaseEntityProperty { get; set; }
}
public class InheritanceDerivedEntity : InheritanceBaseEntity
{
    public int DerivedEntityProperty { get; set; }
}

public DbSet<InheritanceBaseEntity> InheritanceBaseEntities { get; set; }
public DbSet<InheritanceDerivedEntity> InheritanceDerivedEntities { get; set; }

// use .OfType<InheritanceDerivedEntity>() to get entities that have a 
//     non-null 'value' for the related properties
var inheritanceEntities = dbContext.Set<InheritanceBaseEntity>().ToArray();