Question

the following code for some bizarre reason gives me a value for each row in the table. I just want unique values :

public IQueryable<WasteIndicatorItem> FindAllEWC()
{

    var results = (from x in this._db.WasteIndicatorItems
                   orderby x.EWC
                   select x).ToList();



    return results.OrderBy(s => s.EWC).Distinct().AsQueryable();
}

I’ve tried moving the .Distinct() all over the place, before the ToList ETC. What am i doing wrong must be something simple, cheers for reading..

So in my results I get :

13
13
13
12345
12345

rather than :

13
12345

TABLE STRUCTURE IS :

CREATE TABLE [dbo].[WasteIndicatorItem](
    [WasteIndicatorItemId] [int] IDENTITY(1,1) NOT NULL,
    [WasteId] [int] NOT NULL,
    [WasteIndicatorId] [int] NOT NULL,
    [EWC] [varchar](6) COLLATE Latin1_General_CI_AS NOT NULL,
    [WasteHazardCodeId] [int] NOT NULL,
    [Quantity] [money] NOT NULL,
    [Notes] [varchar](4000) COLLATE Latin1_General_CI_AS NULL,
    [EnteredById] [int] NOT NULL,
    [Entered] [datetime] NOT NULL,
    [LastModifiedById] [int] NULL,
    [LastModified] [datetime] NULL,
 CONSTRAINT [PK_IndicatorItem] PRIMARY KEY CLUSTERED 
(
    [WasteIndicatorItemId] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

Answer 1

You have two choices:

1. Use GroupBy and keep everything on the SQL side (preferred). You would group by the property you’re interested in that defines uniqueness to you.
2. Use AsEnumerable to bring everything down, then use the overloaded Distinct method that accepts an IEqualityComparer. This usually isn’t a good idea (unless the result set is small) since all the matching results are returned, and less processing is done on the SQL side.

Implementing the first solution looks like this:

var results = _db.WasteIndicatorItems
                 .OrderBy(x => x.EWC)
                 .GroupBy(x => x.EWC)
                 .Select(x => x.First());