CODEWITHSUNDEEP
c#linq
anand
anand

Reputation: 1579

Linq Select Max Value Dataset

I have 3 table connected with primary and foreign concept.

model -> studentRecord

public class studentRecord
{
    public string studentName{ get; set; }
    public int year{ get; set; }
}

Table 1 -> student

studentId  studentName
----------------------
 1             Sam
 2             Mani
 3             rajah

Table 2 -> subject

subjectid    subjectName
------------------------
  1            english
  2             maths
  3            physics

table 3 -> register

 registerId   studentId   subjectid    Year
--------------------------------------------
     1           1              1       1
     2           1              2       1
     3           1              3       1
     4           1              1       2
     5           1              2       2
     6           1              3       2

i want to get the record of the second year of the student.
my linq code

var op = (from student in db.student.where(x => x.studentId == 1)
          join register in db.register
          on student.studentId equals register.studentId
          select new studentRecord{studentName = student.studentName, year = register.Year}).ToList<studentRecord>().Max(x => x.Year)

I am getting error. Is there any appoach with good performance. Thanks in advance

Upvotes: 1

Views: 137

Answers (1)

gembird
gembird

Reputation: 14053

Have tested the query in Linqpad and the following query works just fine for me.

void Main()
{
    var op = (from student in Students.Where(x => x.StudentId == 1)
              join register in Registers
              on student.StudentId equals register.StudentId
              select new {student = student.StudentName, Year = register.Year})
    .Max(x => x.Year);

    op.Dump();
}

And profiler shows the following SQL.

exec sp_executesql N'SELECT MAX([t1].[Year]) AS [value]
FROM [student] AS [t0]
INNER JOIN [register] AS [t1] ON [t0].[studentId] = [t1].[studentId]
WHERE [t0].[studentId] = @p0',N'@p0 int',@p0=1

Anyway what you probably want is this:

from student in Students.Where(s => s.StudentId == 1)
join register in Registers.Where(r => r.Year == Registers.Max(x => x.Year))
on student.StudentId equals register.StudentId
select new studentRecord
    {
        studentName = student.StudentName, 
        year = register.Year
    })
.ToList<studentRecord>();

Students is in your code db.student etc.

Upvotes: 1

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