The method Distinct is not supported

问题

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?

回答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.

回答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();

来源：https://stackoverflow.com/questions/13127173/the-method-distinct-is-not-supported