I have a problem in Linq to SQL to return a query? in method

Question

5.00/5 (1 vote)

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Please read this code that i found in msdn:

            class Person
            {
                public string Name { get; set; }
            }

            class Pet
            {
                public string Name { get; set; }
                public Person Owner { get; set; }
            }

            public static void GroupJoinEx1()
            {
                Person magnus = new Person { Name = "Hedlund, Magnus" };
                Person terry = new Person { Name = "Adams, Terry" };
                Person charlotte = new Person { Name = "Weiss, Charlotte" };

                Pet barley = new Pet { Name = "Barley", Owner = terry };
                Pet boots = new Pet { Name = "Boots", Owner = terry };
                Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
                Pet daisy = new Pet { Name = "Daisy", Owner = magnus };

                List<person> people = new List<person> { magnus, terry, charlotte };
                List<pet> pets = new List<pet> { barley, boots, whiskers, daisy };

                // Create a list where each element is an anonymous 
                // type that contains a person's name and 
                // a collection of names of the pets they own.
//////////////////////////////////////////////////////////////////////////////////
I want to create a method for this query in below and Instead of this code i use a method!
//////////////////////////////////////////////////////////////////////////////////
                var query =
                    people.GroupJoin(pets,
                                     person => person,
                                     pet => pet.Owner,
                                     (person, petCollection) =>
                                         new
                                         {
                                             OwnerName = person.Name,
                                             Pets = petCollection.Select(pet => pet.Name)
                                         }); 
////////////////////////////////////////////////////////////////////////
               foreach (var obj in query)
                {
                    // Output the owner's name.
                    Console.WriteLine("{0}:", obj.OwnerName);
                    // Output each of the owner's pet's names.
                    foreach (string pet in obj.Pets)
                    {
                        Console.WriteLine("  {0}", pet);
                    }
                }
            }

This code produces the following output:

Hedlund, Magnus:
Daisy
Adams, Terry:
Barley
Boots
Weiss, Charlotte:
Whiskers

Posted 29-Jan-12 12:04pm

best or not

Updated 29-Jan-12 18:54pm

v5

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Comments

[no name] 29-Jan-12 21:45pm

Format code snippets

[no name] 29-Jan-12 21:46pm

OK, I've read the code.

Now, do you have an actual question?

Mohamed Ahmed Abdullah 30-Jan-12 0:29am

Where is the problem????

best or not 30-Jan-12 0:49am

I dont know what kind of return value that i have here to return in my method?

2 solutions

Solution 1

You could use the dynamic key word as your return type. However that uses latebounding through reflection and you don't get the benefit of intellisense at compile time. Why don't you rather create a strongly typed object and project the result to an instance of that type?

C#

var query =
                people.GroupJoin(pets,
                                 person => person,
                                 pet => pet.Owner,
                                 (person, petCollection) =>
                                     new PetOwners
                                     {
                                         OwnerName = person.Name,
                                         Pets = petCollection.Select(pet => pet.Name)
                                     });

Try to avoid creating an anonymous type if you going to use the same query in multiple scenarios. Here's a good link that may also help you.
http://msmvps.com/blogs/jon_skeet/archive/2009/01/09/horrible-grotty-hack-returning-an-anonymous-type-instance.aspx[^]

Posted 29-Jan-12 19:06pm

Dean Oliver

Comments

Tech Code Freak 12-Feb-12 1:02am

5up!

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Amir Mahfoozi · Accepted Answer · 2012-01-29T22:22:00

I think this is your answer :
http://stackoverflow.com/questions/534690/linq-to-sql-return-anonymous-type[^]

So you need to define a class like this :

C#

public class PersonPet
{
    public string OwnerName { get; set; }
    public List<string> Pets  { get; set; }
}

And the return type will be IQueryable<PersonPet>

Your code should look like this :

C#

IQueryable<PersonPet> query =
    people.GroupJoin(pets,
                     person => person,
                     pet => pet.Owner,
                     (person, petCollection) =>
                         new PersonPet()
                         {
                             OwnerName = person.Name,
                             Pets = petCollection.Select(pet => pet.Name)
                         });

I can't test it so do some manipulation if it needs.