Visual error: 'Object reference not set to an instance of an Object.'

Excuse me: how can you let the Classrom. Professor of value read

CodePudding user response:

Specified student entity class there is no literature in this field, can't use it so

CodePudding user response:

That should be how to write?

CodePudding user response:

. Sorry just didn't look closely, since have the item. The classrom words should not be problem of a class
Is the SQL you write wrong, can run the SQL statement? If no good
Select * from Students as s left the join (select ID from Classroms where Professor='Li na) as c on s.C lassId=c.I d
Try this sentence

CodePudding user response:

reference 3 floor kun jins kao kun jins kao response:

. Sorry just didn't look closely, since have the item. The classrom words should not be problem of a class
Is the SQL you write wrong, can run the SQL statement? If no good
Select * from Students as s left the join (select ID from Classroms where Professor='Li na) as c on s.C lassId=c.I d
Try this sentence

Select * from Students as s left the join (select * from Classroms where Professor='Li na) as c on s.C lassId=c.I d

CodePudding user response:

Thank you,, I use the join EF (),

CodePudding user response:

reference kun jins kao, 4/f, kun jins kao response:

Quote: refer to the third floor kun jins kao kun jins kao response:

. Sorry just didn't look closely, since have the item. The classrom words should not be problem of a class
Is the SQL you write wrong, can run the SQL statement? If no good
Select * from Students as s left the join (select ID from Classroms where Professor='Li na) as c on s.C lassId=c.I d
Try this sentence

Select * from Students as s left the join (select * from Classroms where Professor='Li na) as c on s.C lassId=c.I d

Thank you for your reply, sorry, have no points, just now,