Linq to SQL一对多关系加入

Question

I have trouble making joins. Overall query is going to be huge, but basicly, user inputs 1 ID, and data for report is going to be populated from database.

There can be one to many relationship. I made ... join oneToManyTable_ in db.tableA on ID equals oneToManyTable_.DeviceId into oneToManyTable . This expression returns IEnumerable. Trouble now - each of those entities I have to join more tables. How do I do that? If i write ... join anotherTable in db.tableB on oneToManyTable.ID equals anotherTable.ID into oneToManyTable , it yells to me, that oneToManyTable is IEnumerable. Hope you could understand my trouble.

Answer 1

It was easier if you could have been more specific. Anyway, I think your problem is that you don't use select after your first join. The format should be like this:

var output =
from class1 in context.Table1
join class2 in context.Table2 
    on class1.ID equals class2.DeviceID
select new { Class1 = class1, Class2 = class2 } into firstJoin
join class3 in context.Table3 
    on firstJoin.Class1.ID equals class3.ID
select new { firstJoin, Class3 = class3 }

This will join your three classes on their ID and also give you all their properties in output.