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 do not need a foreach loop in this case, you can use group join to create the dictionary straight from linq which should give you better performance.

dict=(from DataValue d in dt.DataValues
           where sensorIDs.Contains(d.SensorID)
       group d by d.DataID 
           into datavalues
       join data in dt.Datas 
           on datavalues.Key equals data.DataId
       select new { 
         Key = data, 
         Value = datavalues
       }).ToDictionary(a=>a.Key,a=>a.Value.ToList());

or you can use linq expression methods

dict = dt.DataValues.Where(d=>sensorIDs.Contains(d.SensorID))
            .GroupBy(a=>a.DataID)
             .Join(dt.Datas,a=>a.Key,a=>a.DataId,
                    (a,b)=>new{Key=b,Value=a.ToList()})
        .ToDictionary(a=>a.Key,a=>a.Value);