具有非空值类型属性的对象上的LINQ DefaultIfEmpty问题

Question

Requirement

1. I need to join Table1 and Table2
2. The key between two tables are ID which is System.Guid type and is non-nullable value type
3. If Table2.ID is null, I need to get null record from Table1.

LINQ syntax I wrote is as follows.

from records in DBContext.Table1
join history in DBContext.Table2 into recordhistory
from records in recordhistory.DefaultIfEmpty()
select (n => n);

The error I got is "The null value cannot be assigned to a member with type System.Guid which is a non-nullable value type."

Can someone advise me on this? Thank you very much.

Answer 1

Assuming you have an ID property, following should work as inner join:

var result = DBContext.Table1
              .Join(DBContext.Table2, t1 => t1.ID, t2 => t2.ID, (t1, t2) => t1);

Answer 2

I guess, the query, you provided, shoulg give an error, saying that on statement should be specified. So, I guess it should look somewhat like this:

from records in DBContext.Table1
join history in DBContext.Table2 on records.ID equals history.ID into temp
from recordhistory in temp.DefaultIfEmpty()
select new { Record = records, History = recordhistory };