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How to create Dynamic Linq Queries

Posted on 2011-09-12
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Last Modified: 2012-05-12
I have a table with many fields. I can use LINQ to make selections with filters and sort expressions. My problem is that my filters and sorts cannot be coded at compilation time. They come from the user inputs at run time and they can be very general. For example, the user may decide to pick records that have (field1>(field2+field4) && field3==5) || (field4==(field2*field4) && field9.substring(7,5)==”hello”), etc. I think that you can code it with predicates. Have you done that? If so, can you show me some code fragments.
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Question by:JoseHidalgo
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by:käµfm³d 👽
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wdosanjos earned 500 total points
ID: 36538538
If you are using LINQ to Entities, you can leverage the ObjectSet<T>.Where method to dynamically build a query string with your criteria.  Here is an example:

using (var context = new YourEntities())
{
	var prms = new List<ObjectParameter>();
	
	prms.Add(new ObjectParameter("@field3", 5));
	prms.Add(new ObjectParameter("@field9", 9));
	
	var query = context.YourObjectSet.Where(
		"(it.field1>(it.field2+it.field4) && it.field3==@field3) || (it.field4==(it.field2*it.field4) && it.field9.substring(7,5)==@field9)",
		prms.ToArray()
		);
}          

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ObjectQuery<T>.Where Method
http://msdn.microsoft.com/en-us/library/bb338811.aspx

I hope this helps.
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by:JoseHidalgo
ID: 36557042
Thanks
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