CODEWITHSUNDEEP
c#stringlinqgenerics
Kianoush
Kianoush

Reputation: 59

Cannot implicitly convert type 'System.Collections.Generic.List in asp mvc

i need join 4 tabel with Linq . but it show me this error :

Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<>' to 'System.Collections.Generic.List' E:\MyProject\GoKhoda\GoKhoda\Areas\Classes\StudentsFunc.cs 20 20 GoKhoda

this is my code : 

public List<Tbl_Students> ShowAllStudents()
    {
        var qstudent = from s in _db.Tbl_Students
                       join pr in _db.Tbl_Pye_Reshte on s.StudentID equals pr.StudentID
                       join r in _db.Tbl_Reshte on pr.ReshteID equals r.ReshteID
                       join p in _db.Tbl_Paye on pr.PayeID equals p.PayeID
                       orderby p.PayeID descending
                       select new { StudentName = s.StudentName, StudentFamily = s.StudentFamily, StudentImage = s.StudentImage, StudentPayeName = p.PayeName, StudentReshtName = r.ReshteName };
        return qstudent.ToList();
    }

Why Show Me Error ? How can i solve this ?

Upvotes: 2

Views: 3331

Answers (3)

MakePeaceGreatAgain
MakePeaceGreatAgain

Reputation: 37000

Use this:

var qstudent = from s in _db.Tbl_Students
    join pr in _db.Tbl_Pye_Reshte on s.StudentID equals pr.StudentID
    join r in _db.Tbl_Reshte on pr.ReshteID equals r.ReshteID
    join p in _db.Tbl_Paye on pr.PayeID equals p.PayeID
    orderby p.PayeID descending
    select new Tbl_Students { StudentName = s.StudentName, StudentFamily = s.StudentFamily, StudentImage = s.StudentImage, StudentPayeName = p.PayeName, StudentReshtName = r.ReshteName };
return qstudent.ToList();

Select new { ... } will just create an anonymous type whch can´t be converted to anything except object.

Just as an aside: you should consider naming your types depending on what an entity is within your application, in your example Student, not the table where the entity is stored.

Upvotes: 1

Pylyp Lebediev
Pylyp Lebediev

Reputation: 2121

The issue it that anonymous type is a return type from your LINQ query. This anonymous type is defined by compiler based on the names and types specified in the select new {} statement.

To fix it, you can define a new type Student

public class Student
{
    public string StudentName { get; set; }
    public string StudentFamily { get; set; }
    public byte[] StudentImage { get; set; }
    public string StudentPayeName { get; set; }
    public string StudentReshtName { get; set; }
}

and then use Student type in LINQ's select statement and as return type for the ShowAllStudents method

public List<Student> ShowAllStudents()
{
    var qstudent = from s in _db.Tbl_Students
                   join pr in _db.Tbl_Pye_Reshte on s.StudentID equals pr.StudentID
                   join r in _db.Tbl_Reshte on pr.ReshteID equals r.ReshteID
                   join p in _db.Tbl_Paye on pr.PayeID equals p.PayeID
                   orderby p.PayeID descending
                   select new Student { StudentName = s.StudentName, StudentFamily = s.StudentFamily, StudentImage = s.StudentImage, StudentPayeName = p.PayeName, StudentReshtName = r.ReshteName };
    return qstudent.ToList();
}

Upvotes: 1

MacakM
MacakM

Reputation: 1820

Instead of an anonymous object use your model class in select. Then you can return List<StudentModel> instead of List<object>.

Upvotes: 0

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