Question

Hi and thanks for taking the time to answer my question.

After a year and a half of working with Java, I’ve decided to switch back to .NET. I must say that I feel at home in VS2012.

While working with Java I came across an implementation of hibernate that enabled for creating dynamic queries easily.

Imagine I had a form with 5 fields of which only one, any one, must be populated in order for me to filter the results by.

is there a way I can do the following in C#:

if(txtMunicipality.text.length > 0){
   (x => x.municipality == txtMunicipality.text)
}

if(chkboxIsFinished){
   (x => x.isfinished == true)
}

etc..

So I ccheck for every field and if the value has been populated then add that criteria to the query.. and after i’m done with the checks i execute the query. Is there a way to do this in C#?

Answer 1

Yes, it is possible. The simplest way is with delegates, especially the anonymous ones.

For example:

Func<YourEntity, bool> filter = (_ => true); // Default value.

if (txtMunicipality.text.length > 0)
{
    filter = (x => x.municipality == txtMunicipality.text);
}
else if (chkboxIsFinished)
{
    filter = (x => x.isfinished == true);
}

Then you can use the filter delegate in a query, for example in a Where statement (which I suppose was your intent – if not, the example is still relevant, just not directly applicable)

/ LINQ syntax.
var entities = from e in context
               where filter(e)
               select e;

// Method syntax.
var entities = context.Where(x => filter(x));
// Or simply:
var entities = context.Where(filter);