Join two tables using linq, and fill a Dictionary of them

Question

I\'ve been searching how to join two tables (Data and DataValues, one to many) and fill a dictionary of type .

The records of Data(s) might be thousands (e.g. 500,00

Answer 1

You're querying way too many times. You can do this in one query.

var dict = (from d in dt.Datas
            join dV in dt.DataValues on d.DataID equals dv.DataID
            where SensorIDs.Contains(dv.SensorID)
            select new { d, dV }).ToDictionary(o => o.d, o => o.dV.ToList());

In your foreach loop, you are fetching all Data and for each of them, you are doing the same thing.

Edit: Now that wasn't very clear, but I think you want to join only the DataValues that are in the SensorIDs array. In this case:

var dict = (from d in dt.Datas
            let dV = (from dataValue in dt.DataValues
                      where SensorIDs.Contains(dataValue.SensorID) &&
                            dataValue.DataID = d.DataID
                      select dataValue)
            select new { d, dV }).ToDictionary(o => o.d, o => o.dV.ToList());