IQueryable question

Question

In regards to my code block below. Would the use of IQueryable<Sports_Leagues_Level> 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);

}

Vulpes · Answer

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 Hobbs · Answer

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 Trivedi · Answer

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 Hengbin · Answer

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 ();

Sam Hobbs · Answer

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.

Rich · Answer

Sam thanks for the outline. I will take some time and study this.

Sam Hobbs · Answer

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); } } }

Rich · Answer

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 Hobbs · Answer

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?

Rich · Answer

Thanks for all the input. This helps me going forward. I think I will stick with the var keyword for this scenario.