Question

Not sure if this is possible or if I’m expressing correctly what I’m looking for, but I have the following piece of code in my library repeatedly and would like to practice some DRY. I have set of SQL Server tables that I’m querying based on a simple user-supplied search field ala Google. I’m using LINQ to compose the final query based on what’s in the search string. I’m looking for a way to use generics and passed in lambda functions to create a reusable routine out of this:

string[] arrayOfQueryTerms = getsTheArray();  var somequery = from q in dataContext.MyTable                 select q;  if (arrayOfQueryTerms.Length == 1) {     somequery = somequery.Where<MyTableEntity>(         e => e.FieldName.StartsWith(arrayOfQueryTerms[0])); } else {     foreach(string queryTerm in arrayOfQueryTerms)     {         if (!String.IsNullOrEmpty(queryTerm))         {             somequery = somequery                          .Where<MyTableEntity>(                             e => e.FieldName.Contains(queryTerm));         }     } } 

I was hoping to create a generic method with signature that looks something like:

private IQueryable<T> getQuery(     T MyTableEntity, string[] arrayOfQueryTerms, Func<T, bool> predicate) 

I’m using the same search strategy across all my tables, so the only thing that really differs from usage to usage is the MyTable & MyTableEntity searched and the FieldName searched. Does this make sense? Is there a way with LINQ to dynamically pass in the name of the field to query in the where clause? Or can I pass in this as a predicate lambda?

e => e.FieldName.Contains(queryTerm) 

I realize there a million and a half ways to do this in SQL, probably easier, but I’d love to keep everything in the LINQ family for this one. Also, I feel that generics should be handy for a problem like this. Any ideas?

Answer 1

It sounds like you’re looking for Dynamic Linq. Take a look here. This allows you to pass strings as arguments to the query methods, like:

var query = dataSource.Where('CategoryID == 2 && UnitPrice > 3')                       .OrderBy('SupplierID'); 

Edit: Another set of posts on this subject, using C# 4’s Dynamic support: Part 1 and Part 2.