Filter data before lookup(join) two collections in mongodb

855

I'm writing a function which will join two collections and two filters for each.

public class Teacher
{
public string Id{ get; set; }
public string Name{ get; set; }
public string TeacherFilter{ get; set; }
...
}

public class Student
{
public string Id{ get; set; }
public string Name{ get; set; }
public string StudentFilter{ get; set; }
public string TeacherId{ get; set; }
...
}

public class TeacherStudents
{
public string Id{ get; set; } -- from teacher
public string Name{ get; set; } -- from teacher
public IEnumerable<Student> Students{get;set;}
}

public class TeacherStudents
{
public string Id{ get; set; } -- from teacher
public string Name{ get; set; } -- from teacher
public IEnumerable<Student> Student{get;set;}
}

public class TeacherStudent
{
public string Id{ get; set; } -- from teacher
public string Name{ get; set; } -- from teacher
...
public Student Student{get;set;}
}

Get(string TeacherFilter,string StudentFilter).

Here is how i implement it

var query = teacherCollection.Aggregate().Match(x => x.TeacherFilter== TeacherFilter); //filter teach
var query1 = query
.Lookup<Teacher, Student, TeacherStudent>(studentCollection, t => t.Id, s => s.TeacherId, l => l.Student)
.Unwind(x => x.Student, new AggregateUnwindOptions<TeacherStudent>())
.Match(x => x.StudentFilter== StudentFilter) //filter student

For the teacher collection, useless data has been filter out before lookup which will reduce the data size when doing the lookup(join). But for the student collection, the match stage is appended after the lookup. so does all the data from student will join with teacher behind the scenes? is it possible to filter out some student data before the lookup?

Peter_in_2780

Step one: Refer to the red link at the top of this page.

Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012

OriginalGriff

Teachers shouldn't lookup students. You end up on all sorts of Registers if you do that, as well as being banned from teaching.

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Richard Deeming

So you posted this in QA[^]; reposted it in the database forum[^]; and now you've posted a third copy in the forum which explicitly forbids programming questions. Your impatience and inability to follow the rules clearly know no bounds. :doh:

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