实体框架中的空值

Question

var query = from section in load_sections.Sections
            join course in load_sections.Courses
                on section.Course_Id equals course.Course_Id
            join faculty in load_sections.Faculties
                on section.Faculty_Id equals faculty.Faculty_Id
            select section;

I have some null values in my section.Faculty_Id which will not be equal to any row in faculty.Faculty_Id and it is just returning the records where section.Faculty_Id is not null...If section.Faculty_Id is not null, then it must return the other remaining fields of Table Courses

Answer 1

If you can't drop the join on faculty for whatever reason, you'll have to construct an outer join:

var query = from section in load_sections.Sections
            join course in load_sections.Courses
                on section.Course_Id equals course.Course_Id
            join faculty in load_sections.Faculties
                on section.Faculty_Id equals faculty.Faculty_Id into faculties
            from f in faculties.DefaultIfEmpty()
            select section;

This executes a GroupJoin with Faculties . The effect of the subsequent from f in faculties is that the grouping is flattened again by a SelectMany . .DefaultIfEmpty() creates the outer join.