The method Distinct is not supported

Question

I am using Linq to Entities and am getting this error

The method Distinct is not supported

On this line of code

var typeIds = _context.AttributeValues.Select(av => av.AttributeTypeId).Distinct();

Why is this?

Mincemeat

Are you using SQL Server or another database with its own LINQ-to-Entities provider? – Hofmann

Or is this WCF data services? – Potboiler

I am using SQL Server and WCF data services. – Mincemeat

Answer 1

A solution is to define a WCF Data Service using (server-side) the QueryByCube method provided by my product AdaptiveLINQ (www.adaptivelinq.com). This method transforms a projection (expressed by the select operator) in an aggregation.

You have just to define a cube with one dimension : AttributeTypeId

av => av.AttributeTypeId

Define a Data Service providing the queryable collection:

yourDbContext.AttributeValues.QueryByCube(yourCube);

Now you can query your service using the OData protocol:

http://.../myService.svc/AttributeValues?$select=AttributeTypeId

Or, if your using a C# client:

serviceContext.AttributeValues.Select(x => x.AttributeTypeId);

The advantage of this solution relative to the workaround proposed A J Qarshi is that the distinction is made on the server side.

Sightless

I've approved your edit to the question only after checking your answer. For future reference, it's always better if you can provide a useful description as to why the tag is needed and why does it make sense. – Gilpin

Answer 2

As per MSDN few LINQ methods are not supported which using OData service. Below is a partial list of unsupported methods.

• All
• Any
• Concat
• DefaultIfEmpty
• Distinct
• Except
• Intersect
• Union
• Zip

For a full list of unsupported operations see here

However, as a workaround following statement should work in this case.

var typeIds = _context.AttributeValues
                      .Select(av => av.AttributeTypeId)
                      .AsEnumerable()
                      .Distinct();

Diao