using string as a condition in LINQ

Question

Consider i have the following linq query.I want to specify the condition in where clause as a string as i will make it empty when i wont have any condition.But on doing so i am getting the error : "Cant explitily convert string to bool".I know the reason for the error.I just want to know is there any other alternative to implement the following.

var elements = from element in array
               orderby element descending
               where element > 2
               select element;

string condition="element >"+2;

I want to do the following....

var elements = from element in array
               orderby element descending
               where condition<------------            
                           select element;

PS:I will handle the situation when there is no condition and the where clause is left with no condition.

Thanks in advance...

Use DynamicLinq (dynamiclinq.codeplex.com).

haim770
– haim770

2014-11-17 07:48:46 +00:00
Commented Nov 17, 2014 at 7:48 — haim770
– haim770, Commented Nov 17, 2014 at 7:48

Pieter Witvoet · Accepted Answer · 2014-11-17 08:00:53Z

Query syntax is translated into normal syntax by the compiler, so your example is equivalent to:

var elements = array.OrderByDescending(element => element).Where(element => element > 2);

Both OrderByDescending and Where return an IEnumerable<T>. What Where does is inserting a Func<T, bool> as a filter, so when you iterate over the enumerable, it calls that function for each element and skips the element if the function returns false. If you don't have a condition, you can simply leave out the call to Where:

var elements = array.OrderByDescending(element => element);

If, later, you need to select only certain elements, you can apply your filter to elements:

elements = elements.Where(element => element > 2);

If your filter depends on user input, you can use closures (functions that capture external variables):

public Func<int, bool> CreateFilter(int value)
{
    // This returns a function that 'remembers' the given value:
    return element => element > value;
}

Which can then be used like:

int userInput = 5;
elements = array.OrderByDescending(element => element).Where(CreateFilter(userInput));

Anik Islam Abhi · Accepted Answer · 2014-11-17 08:07:11Z

1

You can split this condition into two like

   var elements = array.OrderByDescending(o => o);
   if (put some condition for active where )
         elements= elements.Where(o=>o>2);

edited Nov 17, 2014 at 8:07

answered Nov 17, 2014 at 7:50

Anik Islam Abhi

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