向实体框架查询添加属性，包括对象本身

Question

Consider this query which is going to be used in a MVC controller:

return
    from student in Students
    where //..
    select student;

the result will be converted to JSON like:

[
    {firstName: "John", lastName="Smith"},
    ...
]

I want to have a query to include courses count like this:

[
    {firstName: "John", lastName="Smith", courseCount: "4"},
    ...
]

first solution is to create a query using anonymous objects like this:

return
    from student in Students
    join course in Customers on course.StudentId equals student.Id 
    where //..
    group by //...
    select new {student.FirstName, student.LastName, CourseCount = courseGroup.Count()};

But in this way I lost the whole object of student. For example if I add Age property to student later, I should update this query and add student.Age to the select part. But in the first solution, the result includes this field automatically.

I'm looking for a more robust solution to do this select, so all changes to the Student class propagate to the result automatically.

Workaround: This would be a solution, but it changes the JSON format and sounds a little tricky. I'm looking for a better solution. (Maybe with dynamic objects!)

select new { Student = student, CourseCount = courseGroup.Count()};

---

EDIT: The desired solution is would be something like this:

select new Student(student){CourseCount = courseGroup.Count()}

Adding CourseCount in a dynamic way!

Answer 1

You could do a left join on the courses which would give you the results that you want.

[code] return from student in Students join course in Customers on course.StudentId equals student.Id

into courseGroup from course in courseGroup.DefaultIfEmpty()

where //..
select new {student.FirstName, student.LastName, CourseCount = courseGroup.Count()};

[code]

If you do a GroupBy it will cancel out the student class and you would then have to do something like... courseGroup.StudentFirstName ... Depending on what your GroupBy looks like.