I'm using LINQ to Entities.
I have a table called Student; it has ID and Name as it's columns. ID is a primary key.
I'd like to be able select the name of the Student and get the amount of Students with the same Name.
So for example I'd have this as my table data.
ID Name
1 Bob
2 Will
3 Bob
After performing the query I'd return a List of Student objects looking like this.
Name Quantity
Bob 2
Will 1
I guess it is kind of similar to how the Tags page of stackoverflow works; It has the name and the quantity.
Anyways, I created a partial class called Student.cs in which I added a Quantity property like this.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace MySite.Models
{
public partial class Student
{
private int _quantity;
public int Quantity
{
get { return _quantity; }
set { _quantity = value; }
}
}
}
I came up with this but I'm getting an error..
public IQueryable<Student> FindStudentsDistinctWithQuantity()
{
/*SELECT Name, COUNT(Name) AS Quantity
FROM Student
GROUP BY Name*/
var students= (from s in db.Students
group s by s.Name into g
select new {Name = g.Key, Quantity = g.Count()});
return students;
}
The error i'm getting says something like Can't convert from type Anonymous to the Student list. Does it have something to do with it not recognizing the quantity field I added in the partial class?
Thanks!
C# Query Expression is an expression that is written by using LINQ query syntax. The LINQ (Language Integrated Query) is a language that is used to construct a query. C# Query Expression contains set of clauses and use query expression similar to SQL.
Expression Class (System. Linq. Expressions) Provides the base class from which the classes that represent expression tree nodes are derived. It also contains static (Shared in Visual Basic) factory methods to create the various node types.
This package has been deprecated as it is legacy and is no longer maintained.
Change your Student
type to look like this:
public partial class Student
{
public Int32 Quantity { get; set; }
public String Name { get; set; }
}
And your query to look like this:
var students = from s in db.Students
group s by s.Name into g
select new Student {
Name = g.Key,
Quantity = g.Count() };
Your method returns an IQueryable<Student>
but you are currently returning an IQueryable<T>
of a projected anonymous type.
You need to refactor your Student
type to have a Name
property of type String
and then project new instances of your Student
type from the expression so that the return type of your expression will match the return type of your method.
Your function returns Student
public IQueryable<Student> FindStudentsDistinctWithQuantity(){ ... }
But your Linq query returns a new type that contains a Name and an Int (count)
>>> select new {Name = g.Key, Quantity = g.Count()});
y-try select new Student{Name = g.Key, Quantity = g.Count()}
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