Duplicate Rows when Data Binding with LINQ to Entities

Question

I have problems binding both a telerik RadGrid and a plain vanilla ASP.NET GridView to the results of the following LINQ to entities query. In both cases the grids contain

Answer 1

It looks to me like you have a borked primary key. The "identity management" aspect of LINQ-to-SQL and EF means that it is obliged to give you back the same instance whenever it sees the same primary key value(s) for the same object type.

For example, given the data:

id     | name       | ...
-------+------------+------
1      | Fred       | ...
2      | Barney     | ...
1      | Wilma      | ...
1      | Betty      | ...

Then if it thinks id is a primary key when iterating over the objects from LINQ, it is forced to give you "Fred", "Barney", "Fred", "Fred". Essentially, when it sees id 1 again, it doesn't even look at the other columns - it simply fetches the instance with id 1 from the identity cache - and gives you the same Fred instance it gave you previously. If it doesn't think id is a primary key, it will treat each row as a separate object (and so what if it has the same value in one of the fields as another record - that isn't exactly unusual).

I would advise checking that any fields you have marked as a primary key (in your DBML/EDM model) really are unique per row. In the case above, the id column clearly doesn't represent a unique identifier, so is not suitable as a primary key. Just unmark it as such in the LINQ-to-SQL / EF designer.

---

update: in particular, look at the "Entity Key" property for the various properties in the designer - especially if you are querying a view. Check that "Entity Key" is only set to true for suitable columns (i.e. those that make the row unique). If it is set incorrectly, set it to false. This is also visible as the yellow key icon - this should only appear on things that genuinely are unique identifiers for a record.

Answer 2

And if you wrap the link query in a parenthesis and use the .Distinct() extension?

public IEnumerable<DirectoryPersonEntry> FindPersons(string searchTerm)
{
    DirectoryEntities dents = new DirectoryEntities();
    return (from dp in dents.DirectoryPersonEntrySet
           where dp.LastName.StartsWith(searchTerm) || dp.Extension.StartsWith(searchTerm)
           orderby dp.LastName, dp.Extension
           select dp).Distinct();
}

Answer 3

One difference between your working and broken queries is the orderby clause. I found a documented bug in the orderby implementation in Linq to Entities... there may be others.

Try removing orderby from the broken query and see if you still get duplicates.

Another difference is the OR in the where clause. Try using only the first part [ where dp.LastName.StartsWith(searchTerm) ] and see if you still get duplicates.

Answer 4

I faced the same problem and solved it with a workaround. I am posting it here as it might help others coming here.

instead of select dp , use

select new <ObjectName>
{
a = v.a
b = v.b
}.

This will not return duplicates.