Question

may someone could help me on one problem in query LINQ to SQL Visual Basic.

My database has three tables,

* Students(StudentID, StudentName), * Class(ClassID, ClassDate), * Attendance(StudentID, ClassID) which Attendance tables is the junction table between Students and Class. 

For example:

Students

StudentsID………….StudentName

1001………………….Smith

1002………………….John

1003………………….Bob

Class

ClassID…………ClassDate

1………………….1/1/2009

2………………….1/3/2009

3 …………………1/7/2009

Attendance

StudentID…………ClassID

1001 ……………….1

1002 ……………….1

1003 ……………….1

1001 ……………….2

1003 ……………….2

1001 ……………….3

1002 ……………….3

1003 ……………….3

I have try the query Visual Basic LINQ to SQL below to list all the student and the count number of attendance in a range of date.

1 Dim db = New AttendanceControllerDataContext 2 3 Dim result = From std In db.Students _ 4 Select std.StudentID, _ 5 std.StudentName, _ 6 Attendance = std.Attendances.Count() 7 8 GridView1.DataSource = result 9 GridView1.DataBind() 

When I try this, it gives me:

StudentID……..StudentName…..Attendance

1001……………Smith…………………3

1002……………John………………….2

1003……………Bob…………………..3

In line 6, Attendance I want to count according to the range of date in the Class Table, For example if I selected a range of date between 1/2/2009 and 1/7/2009, then I have tried the following code:

 1   Dim db = AttendanceControllerDataContext   2   Dim result = From std In db.Students, atd In db.Attendances _  3                Where atd.studentID = std.studentID _  4                Select std.studentID, _  5                std.studentName, _  6                Attendance = atd.Class.date >= 1/2/2009 _  7                And atd.Class.date <= 1/7/2009  std.Attendances.Count()  8   GridView1.DataSource = result  9   GridView1.DataBind() 

The result is:

StudentID……..StudentName…..Attendance

1001……………Smith…………………2

1001……………Smith…………………2

1002……………John………………….1

1003……………Bob…………………..2

1003……………Bob…………………..2

However, I just wanted a list that look like below only:

StudentID……..StudentName…..Attendance

1001……………Smith…………………2

1002……………John………………….1

1003……………Bob…………………..2

How can I do this? Any suggestion? Thank in advance..

Answer 1

Instead of

Attendance = std.Attendances.Count() 

in your first code sample use

Attendance = std.Attendances.Where(Function(att) att.Class.ClassDate >= '1/2/2009' And att.Class.ClassDate <= '1/7/2009').Count()