Hierarchical Entity Framework Query Exception

Question

I am attempting to build up a hierarchical collection using Entity Framework - see the below query - every member in a given company has a parent member - but when trying to execute this I get the following exception:

System.NotSupportedException: The type 'Member' appears in two structurally incompatible initializations within a single LINQ to Entities query. A type can be initialized in two places in the same query, but only if the same properties are set in both places and those properties are set in the same order.

If I remove the ParentMember assign it works - any ideas on what is going on?

        return from c in _Entities.Company
               where c.Deleted == false
                select new Member()
                {
                    Name = c.Name,
                    ParentMember = new Member() 
                    {
                        Name = c.ParentMember.Name
                    }
                };

chris · Accepted Answer · 2010-11-09 16:00:45Z

12

I haven't tried this, but the error message gives you a clue: you're not setting the same properties in the same order in both places.

What happens if you try setting an ID property on the outer Member()?

answered Nov 9, 2010 at 16:00

chris

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2 Comments

Robert W Over a year ago

I've just updated the code in the question to reflect the actual code - I have exactly the same properties being set in the same order with the exception of setting the ParentMember property of the ParentMember, if that makes sense.

chris Over a year ago

Actually, you're still not setting all the same params: the outer has Name and ParentMember, while you're only setting the Name for the inner. Try assigning the property a null.

Bohdan Lyzanets · Accepted Answer · 2013-04-09 13:16:11Z

2

Try

return (from c in _Entities.Company
               where c.Deleted == false
                select new
                {
                    c.Name,
                    ParentMember = new
                    {
                        c.ParentMember.Name
                    }
                })
.AsEnumerable()
.Select(c=> new Member
                {
                    Name = c.Name,
                    ParentMember = new Member
                    {
                        Name = c.ParentMember.Name
                    }
                });

answered Apr 9, 2013 at 13:16

Bohdan Lyzanets

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1 Comment

Shaul Behr Over a year ago

+1 This catch-22 situation just bit me, and this was the solution I came up with independently. Less elegant than I was hoping, and a little wasteful, since we have to do double the object instantiation, but nonetheless effective.

Boggin · Accepted Answer · 2013-03-20 11:59:18Z

1

You will end up with a recursion of Member records when you try to retrieve the same fields in each one. You can't just make the last parent record equal to null.

I would retrieve what I could and then build up the record with further queries. Note that your Company entity will require a ParentId field or similar.

var members = 
  return from c in _Entities.Company
  select new Member()
  {
    Name = c.Name,
    ParentId = c.ParentId
  };

Now iterate and add in the parent records.

foreach (var member in members)
{
  member.ParentMember = new Member 
    {
      Name = _Entities.Company.First(c => c.Id == member.ParentId).Name
    };
}

edited Mar 20, 2013 at 11:59

answered Mar 20, 2013 at 11:52

Boggin

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