Passing a delegate as a parameter (LINQ) ... C#

[Jose_49]

Helloooooooo!!!!!! I'll keep this short. I have forgotten how it is called (and its syntax) when you pass a delegate as a parameter for doing the same query. I thought I had bookmarked the page where I saw that...

 

In english: 

 

Instead of doing something like this: 

public void SearchMethod(string value, int flag)
{
     if(flag == 1)
     {
          DBContext.Where(x => x.Contains(value));
     }

     else if(flag == 2)
     {
          DBContext.Where(x => x.Contains(value)).GroupBy(x => x.id)
     }
     else if(flag == 3)
    { 
          DBContext.Where(x => x.Contains(value)).GroupBy(x => x.Name)
    }
}

I would pass a Func<> as a paramter and I'll save myself from grabbing all those "if"s

public void SearchMethod(Func<string> query, int flag)
{
     //Do something with the query and save all those if
     // I don't remember the syntax used!
}

[SledgeNZ]

I'll keep it shorter, look up predicates.

 

: D

 

Ok, a bit more help, stackoverflow generally has the best examples:

http://stackoverflow.com/questions/556425/predicate-delegates-in-c-sharp
 

[Jose_49]

  On 14/01/2015 at 14:33, SledgeNZ said:

I'll keep it shorter, look up predicates.

 

: D

Thanks Right now I'm not looking for predicates.

 

It's something similar to this answer:

http://codereview.stackexchange.com/a/5506

 

Edit:

Sorry!!!!

Yes, predicates are part of the equation I need to know how to do it with Func<> or Expression Trees...

[Andre S. Veteran]

I don't understand what you're trying to do, but perhaps something like this (assuming DBContext contains DBItems and you actually want them back) ?

public IEnumerable<DBItem> SearchMethod<T>(string value, Func<DBItem, T> groupByFunc)
{
     var filtered = DBContext.Where(x => x.Contains(value));
     return groupByFunc == null
         ? filtered
         : filtered.GroupBy(groupByFunc);
}

It's not a big improvement, I've just bound the common case to a variable, encoded whether to use groupByFunc using a potentially null parameter and delegated the choice of the GroupBy function to the caller; either way the code does the same thing. But it's not clear what you're looking for.

[Jose_49]

Thanks all! This is what I meant:

  Quote

 

t generally helps if you know the specific type of context that you are targeting.

For instance, let's say you are targeting a context that contains a collection of string objects and you wanted to search them. You would define a function like the following which accepted a function like so :

public void SearchMethod(Func<string,bool> query, int flag)
{
switch(flag)
{
case 1:
// Perform your search
DBContext.YourTable.Where(query);
break;
case 2:
DBContext.YourTable.Where(query).GroupBy(x => x.id);
break;
case 3:
DBContext.YourTable.Where(query).GroupBy(x => x.Name);
break;
}

}

Additionally, you could also pass in a function to handle your GroupBy query as well similar to the approach mentioned in this Stack Overflow response.

 

From:

forums.asp.net/p/2033405/5854959.aspx?p=True&t=635584716606703187

 

Thank you guys!!!! :D  Your answers gave me another idea for another part of my project!

[greenwizard88]

Bookmarking this page for later!