如何使用 EntityFrameworkCore 定义父/子关系？

Question

I have a project that uses EntityFrameworkCore to access data from a database.

I am trying to create a parent/children relation for a single object (ie, Category ). My object looks like this

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

    public string Name { get; set; }

    public int? ParentCategoryId { get; set; }

    public Category ParentCategory { get; set; }

    public ICollection<Category> Children { get; set; }
}

The property ParentCategoryId is optional, but when set, it'll determine the parent of the current category. At the same time, when the Children relation is included, I want to be able to pull all the categories where ParentCategoryId equal the id of the current category.

I added the following code in the context to define the relations

protected override void OnModelCreating(ModelBuilder builder)
{
    base.OnModelCreating(builder);
    builder.Entity<Category>(cat =>
    {
        cat.HasMany(x => x.Children).WithOne().HasForeignKey(x => x.ParentCategoryId);
        cat.HasOne(x => x.ParentCategory).WithOne();
    });
}

So when the following code is called I want to get the ParentCategory and all Children of category id 10.

var category = _context.Categories.Where(cat => cat.Id == 10)
                       .Include(x => x.ParentCategory)
                       .Include(x => x.Children)
                       .ToList();

However, the above code gives me the following error

Invalid column name 'ParentCategoryId1'." string

How can I correctly define the relations for ParentCategory and Children ?

Answer 1

You have to use more simple names for navigation properties, otherwise EF getting confused.This code was tested and working properly

public class Category
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public int? ParentId { get; set; }
        public virtual Category Parent { get; set; }

        public virtual ICollection<Category> Children { get; set; }

     }

and dbcontext

       public virtual DbSet<Category> Categories { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {

            modelBuilder.Entity<Category>()
            .HasOne(s => s.Parent)
            .WithMany(m => m.Children)
            .HasForeignKey(e => e.ParentId);

            OnModelCreatingPartial(modelBuilder);
        }