Returning child objects with Entity Framework code first error: Unable to evaluate the expression. Operation not supported. Unknown error: 0x80070057

Question

I keep getting the following error

Unable to evaluate the expression. Operation not supported. Unknown error: 0x80070057

when trying to return a parent object and its children.

The database builds, seeds and has all the relationships defined correctly as far as I can see. I built a smaller model just to test and for the purpose of showing the problem:

Parent object:

public class Person
{
    [Key]
    [Column(Order = 1)]
    public int Id { get; set; }      

    [StringLength(100)]    
    public string Name { get; set; }

    public DateTime DateModified { get; set; }
    public DateTime DateCreated { get; set; }

    public virtual ICollection<Job> Jobs { get; set; }
}

Child object:

public class Job
{
    [Key]
    [Column(Order = 1)]
    public int Id { get; set; }

    [StringLength(100)]
    public string Name { get; set; }    

    public int PersonId { get; set; }

    [ForeignKey("PersonId")]
    public virtual Person Person { get; set; }
}

returning _context.Person works and returns the list of person with null jobs

Returning _context.Person.Include(o => o.Jobs) throws the above error.

This I know is simple stuff and only two very simple tables but I cannot see where the problem lies as I have created this model senario countless times without a problem. I am thinking about rebuilding the project and EF dependencies but would prefer to understand this issue and fix it if possible.

Answer 1

After some considerable hair pulling the following overcame the issue:

The repository method for _context:

  public IQueryable<Person> GetPeople()
    {
        return _context.Person.Include(s => s.Jobs);
    }

The calling code just required a ToList() method:

var people = _repository.GetPeople().ToList();

The people variable now contains a list of person objects each with a list of job objects. Pheeew!!