Using Linq with a DbDataReader

Question

I am trying to make use of the code in this question to implement a query like this:

    public void LoadLive(DbConnection pConnection)
    {
        using (DbDataReader lReader = pConnection.ExecuteReader("..."))
        {
            mList.AddRange(from t in lReader select new MyObject { Name = t.GetString(0) });
        }
    }

When I attempt to compile this (with the extension method in place), I receive this error:

 error CS1934: Could not find an implementation of the query pattern for source type 'System.Data.Common.DbDataReader'.  'Select' not found.  Consider explicitly specifying the type of the range variable 't'.

Am I missing something about how this is supposed to work?

score 2 · Accepted Answer · answered May 28 '11 at 20:34

2

You must call the extension method from the answer in the linked question:

 mList.AddRange(from t in lReader.AsEnumerable() 
                select new MyObject { Name = t.GetString(0) });

answered May 28 '11 at 20:34

Ladislav Mrnka

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This was close, but for convenience, I implemented a Select extension method that does the `AsEnumerable()`. – Dark Falcon Jun 18 '11 at 23:04

score 0 · Answer 2 · edited May 23 '17 at 11:55

0

Unless you are going to write your own extension method, Select, Where, etc all return an IEnumerable and the typical method signature will resemble Func<DbDataReader, myT>. What you are looking for is something like Jon Skeet's sample here.

edited May 23 '17 at 11:55

Community

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answered May 28 '11 at 20:34

IAbstract

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score 0 · Answer 3 · answered May 28 '11 at 20:47

Compiler error CS1934 is produced when no standard query operators are implemented for a given datasource.

In your case (DbDataReader), you could specify the type of t as IDataRecord:

mList.AddRange(from IDataRecord t in lReader
               select new MyObject { Name = t.GetString(0) });

Using Linq with a DbDataReader

3 Answers3