Question

Here’s my SQL query:

Select  <a bunch of columns>
from fields f
join Table1 c1 on c1.fieldID = f.ID and c1.year = 2014
join Table2 fRes on f.ID = fRes.fieldID
join Table3 stst on f.ID = stst.fieldID
join Table4 model on c1.ID = model.yearID
left join Table5 fA on f.ID = fA.fieldID and fA.year = 2014 
left join Table6 nA on f.ID = nA.fieldID and nA.year = 2014 
where  fA.sourcename IS NULL and nA.Sourcename IS NULL

LINQ to SQL:

from f in BasicDataAccess.Data.FieldsList
join c1 in BasicDataAccess.Data.Table1List on f.ID equals c1.fieldID 
join fRes in BasicDataAccess.Data.Table2List on f.ID equals fRes.fieldID
join soilTst in BasicDataAccess.Data.Table3List on f.ID equals soilTst.fieldID
join modelRsNM in BasicDataAccess.Data.Table4List on c1.ID equals modelRsNM.YearID
join fA in BasicDataAccess.Data.Table5List on f.ID equals fA.fieldID into group1
from g1 in group1.Where(fA => fA.Year == reportYear).DefaultIfEmpty()
join nA in BasicDataAccess.Data.Table6List on f.ID equals nA.fieldID into group2
from g2 in group2.Where(nA => nA.Year == reportYear).DefaultIfEmpty()
where g1.sourceName == null && g2.sourceName == null

Issue: the query when executed throws Nullreference exception was unhandled..Object reference not set to an instance of an object error..

What am I missing? Is it possible to reference the left outer join table in where clause? Please help!

Answer 1

As far as I can see, this line

from g1 in group1.Where(fA => fA.Year == reportYear).DefaultIfEmpty()

can produce null if there’s no rows. In this case, when you try to filter it (where g1.sourceName == null) you’ll get null reference (because g1 is null).