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c#design-patternslambdadbdatareader

Avoid code duplication when reading/serializing from DbDataReader?


Consider the FetchData method below. It is designed to avoid duplicating the database query code every time you want to fetch some data from the database.

List<MyData> myData = new List<MyData();
FetchData((IDataReader reader) =>
   {
       myData.Add(new MyData(reader.GetString(0), reader.GetInt32(1)));
   }, "usp_get_my_data");

It works, but it would be nice if this object creation could somehow live inside the FetchData method.

Is there a better approach?

Perhaps FetchData can be modified to return a list of some type X directly?

protected void FetchData(Action<IDataReader> processor, String query)
{
    using (var connection = CreateConnection())
    {
        connection.ConnectionString = ConnectionString;
        connection.Open();

        using (var command = connection.CreateCommand())
        {
            command.CommandType = CommandType.StoredProcedure;
            command.CommandText = query;

            using (IDataReader reader = command.ExecuteReader())
            {
                while (reader.read())
                {
                    processor(reader);
                }
            }
        }
    }
}

Solution

  • Using generics maybe?

    protected IEnumerable<T> FetchData<T>(Func<IDataReader, T> processor, String query)
    {
        using (var connection = CreateConnection())
        {
            connection.ConnectionString = ConnectionString;
            connection.Open();
    
            using (var command = connection.CreateCommand())
            {
                command.CommandType = CommandType.StoredProcedure;
                command.CommandText = query;
    
                using (IDataReader reader = command.ExecuteReader())
                {
                    while (reader.read())
                    {
                        yield return processor(reader);
                    }
                }
            }
        }
    }
    

    Then you can use the enumeration however you want:

    var myData = FetchData<MyData>(reader => new MyData(reader.GetString(0), reader.GetInt32(1)), "usp_get_my_data").ToList();