IQueryable question

Rich

14y2.4kLINQ

In regards to my code block below. Would the use of IQueryable be better than the var keyword, and if so how would I implement it.

public void GetTeams()

{

var Teams = from sll in db.Sports_Leagues_Level

join nba in db.nba_Team_Names on sll.ID equals nba.SLLid

join league in db.Sports_Leagues on sll.Leagues equals league.Id

select new

{

SllId = sll.ID,

Team = nba.Abreviated_Long,

League = league.LeaguesAbr

};

foreach (var item in Teams)

{

Console.WriteLine("{0} {1} {2}", item.SllId, item.League, item.Team);

}

10 Replies

Know the answer? Post it — somebody with the same question will find it here.

Sam Hobbs14y ago
It is not intended to be an answer; it is just a way to create a sample that can be used for a complete simple sample of the problem. If you can confirm that the table definitions are correct then that will help.
Rich14y ago
Sam, thanks for the outline. I will take some time and study this.

Sam Hobbs14y ago

For the purpose of working with the code, it is possible to create tables in memory. The following I think is a start. I might continue with this in the future. If you want to continue with it then that would be good. By duplicating your conditions in this manner it is possible to work with the code in a functional environment.

 using  System;

 using  System.Collections.Generic;

 using  System.Linq;

 using  System.Text;

 using  System.Data;

 namespace  _157817

 class  Program

 static  DataSet  ds = new  DataSet ("Sports" );

 static  DataTable  Sports = new  DataTable ();

 static  DataTable  Sports_Leagues = new  DataTable ();

 static  DataTable  Sports_Level = new  DataTable ();

 static  DataTable  Sports_League_Level = new  DataTable ();

 static  DataTable  nba_Team_Names = new  DataTable ();

 static  void  Main(string [] args)

 DataColumn  Column;

//

 Column = Sports.Columns.Add("Id" , typeof (Int32 ));

 Column.AutoIncrement = true ;

 Sports.Columns.Add("Name" );

 AddSport("Football" );

 AddSport("Baseball" );

 AddSport("Basketball" );

 Console .WriteLine("Sports" );

 foreach  (DataRow  r in  Sports.Rows)

 Console .WriteLine("\\t{0} {1}" , r.Field<Int32 >(0), r.Field<string >(1));

//

 Column = Sports_Leagues.Columns.Add("Id" , typeof (Int32 ));

 Column.AutoIncrement = true ;

 Sports_Leagues.Columns.Add("Name" );

 AddLeague("League 1" );

 AddLeague("League 2" );

 AddLeague("League 3" );

 Console .WriteLine("Leagues" );

 foreach  (DataRow  r in  Sports_Leagues.Rows)

 Console .WriteLine("\\t{0} {1}" , r.Field<Int32 >(0), r.Field<string >(1));

//

 Column = Sports_Level.Columns.Add("Id" , typeof (Int32 ));

 Column.AutoIncrement = true ;

 Sports_Level.Columns.Add("Name" );

 AddLevel("Level 1" );

 AddLevel("Level 2" );

 AddLevel("Level 3" );

//

 Column = nba_Team_Names.Columns.Add("Id" , typeof (Int32 ));

 Column.AutoIncrement = true ;

 nba_Team_Names.Columns.Add("Name" );

 nba_Team_Names.Columns.Add("Sports_League_Level_Id" , typeof (Int32 ));

//

 Column = Sports_League_Level.Columns.Add("Id" , typeof (Int32 ));

 Column.AutoIncrement = true ;

 Sports_League_Level.Columns.Add("Sports_Id" , typeof (Int32 ));

 Sports_League_Level.Columns.Add("Sports_Leagues_Id" , typeof (Int32 ));

 Sports_League_Level.Columns.Add("Sports_Level_Id" , typeof (Int32 ));

 private  static  void  AddSport(string  Name)

 DataRow  Row;

 Row = Sports.NewRow();

 Row["Name" ] = Name;

 Sports.Rows.Add(Row);

 private  static  void  AddLeague(string  Name)

 DataRow  Row;

 Row = Sports_Leagues.NewRow();

 Row["Name" ] = Name;

 Sports_Leagues.Rows.Add(Row);

 private  static  void  AddLevel(string  Name)

 DataRow  Row;

 Row = Sports_Level.NewRow();

 Row["Name" ] = Name;

 Sports_Level.Rows.Add(Row);

Rich14y ago
Sam, Shen's example did not work for me. I should have provided more detail about the tables that I am querying. "Sports_League_Level" is a table with foreign keys to the Sports, Sports_Leagues, and Sports_Level Tables. "nba_Team_Names" is a table with a column of teams and a foreign key column to the "Sports_League_Level" table. "Sports_Leagues" is a table with a column of league names and no foreign keys. Not sure if this clarifies anything.
Sam Hobbs14y ago
It seems to be very poor design if we are forced to use var. For one thing, it is not object-oriented to be unable to return the object from the method. Since the code is incomplete (I do not now what db.Sports_Leagues_Level is or any of that) I will not explore it further; I have other things to do.

So does the code posted by Shen Hengbin not work?
Rich14y ago
Thanks for all the input. This helps me going forward. I think I will stick with the var keyword for this scenario.
Vulpes14y ago
The query is returning an IQueryable of an anonymous type, and, since by definition an anonymous type doesn't have a name, you have to use 'var'.

The only way around this would be to create a custom class (or struct) with the same fields as the anonymous type and then 'select' new instances of the custom class. You could then replace 'var' with IQueryable of whatever you've called the custom class.

Incidentally, I wrote an article last year about when you should use 'var':

http://www.c-sharpcorner.com/uploadfile/b942f9/when-should-you-use-the-var-keyword-in-C-Sharp/
Sam Hobbs14y ago
I do not like var at all. There are many ways that it is bad.

The main problem is that you don't know what a var is actually, so you don't know what you can do with it. That is frustrating for me.

Another problem is that you cannot pass a var from a function; a var cannot be the return value from a function and a var cannot be a parameter of a function, not even as an "out" parameter.
Jignesh Trivedi14y ago
Hi friend,

I observe your code, I think it doesn't matter whether you use "var" key word or IEnarable. But donot use IQuerable in this code because your query has fixed where criteria and you don't farther filtration on your query. So my opinion is cast in to list.
var Teams = (from sll in db.Sports_Leagues_Level
                        join nba in db.nba_Team_Names on sll.ID equals nba.SLLid
                        join league in db.Sports_Leagues on sll.Leagues equals league.Id
                        select new Sports_Leagues_Level
                        {
                            SllId = sll.ID,
                            Team = nba.Abreviated_Long,
                            League = league.LeaguesAbr
                        }).ToList();
foreach (var item in Teams)
            {
                Console.WriteLine("{0} {1} {2}", item.SllId, item.League, item.Team);
            }
If you use Iquerable here then, its query on your data base more than one time (equal to Teams.count()), so I think it decrease your code performance.
hope this help.
Shen Hengbin14y ago
At first , I don't know who told u to use IQueryable is better than var keyword.

In my opinion I like the var keyword better.

And if you you really want to change the var keyword into the IQueryable

U could use the AsQueryable() , It could help you convert the result to IQueryable

For example (I think Sports_Leagues_Level is your class name ....):

            IQueryable Teams = (from sll in db.Sports_Leagues_Level
                        join nba in db.nba_Team_Names on sll.ID equals nba.SLLid
                        join league in db.Sports_Leagues on sll.Leagues equals league.Id
                        select new Sports_Leagues_Level
                        {
                            SllId = sll.ID,
                            Team = nba.Abreviated_Long,
                            League = league.LeaguesAbr
                        }).AsQueryable();