Can I create an anonymous type collection from a DataReader?

Question

I have this code:

var query = "SELECT * FROM Cats";

var conn = new SqlConnection(sqlConnectionString);

conn.Open();

var cmd = new SqlCommand(query);
var reader = cmd.ExecuteReader();

while (reader.Read())
{
    var CatName = reader.GetString(0);
    var CatDOB = reader.GetDateTime(1);
    var CatStatus = reader.GetInt32(2);
}

I'd like to pull the rows out into an anonymous type collection, which I'd normally do using LINQ to iterate, but I an not sure if it's possible due to the way you have to call .Read() each time to get the next row.

Is there a way to do this?

Answer 1

You can create helper generic method and let compiler infer type parameter:

private IEnumerable<T> Select<T>(DbDataReader reader, Func<DbDataReader, T> selector)
{
    while(reader.Read())
    {
        yield return selector(reader);
    }
}

usage:

var items = SelectFromReader(reader, r => new { CatName = r.GetString(0), CarDOB = r.GetDateTime(1), CatStatus = r.GetInt32(2) });

You can even make the method an extension method on DbDataReader:

public static IEnumerable<T> Select<T>(this DbDataReader reader, Func<DbDataReader, T> selector)
{
    while (reader.Read())
    {
        yield return selector(reader);
    }
}

and use it like that:

var items = reader.Select(r => new { CatName = r.GetString(0), CarDOB = r.GetDateTime(1), CatStatus = r.GetInt32(2) });