Dynamic where clause in LINQ - with column names available at runtime

Question

Disclaimer: I\'ve solved the problem using Expressions from System.Linq.Expressions, but I\'m still looking for a better/easier way.

Consider the following situation :

Answer 1

@Geoff has the best option, justing Dynamic LINQ.

If you want to go the way of building queries at runtime using Lambda though I'd recomment that you use the PredicateBuilder (http://www.albahari.com/nutshell/predicatebuilder.aspx) and have something such as this:

Expression<Fun<T,bool>> pred = null; //delcare the predicate to start with. Note - I don't know your type so I just used T 
if(blacklistFirstName){
  pred = p => p.ContactFirstName.Contains("Blacklisted");
}
if(blacklistLastName){
  if(pred == null){
    pred = p => p.ContactLastName.Contains("Blacklisted"); //if it doesn't exist just assign it
  }else{
    pred = pred.And(p => p.ContactLastName.Contains("Blacklisted"); //otherwise we add it as an And clause
  }
}

And so on for all the columns you want to include. When you get to your query you just need something like this:

var results = db.Customers.Where(pred).Select(c => c);

I've used this to do building of LINQ for searching where there are about 20 different options and it produces really good SQL.

Answer 2

You can turn your where clauses on and off using some logic expressions.

//Turn on all where clauses
bool ignoreFirstName = false;
bool ignoreLastName = false;;
bool ignoreAddress = false;

//Decide which WHERE clauses we are going to turn off because of something.
if(something)
    ignoreFirstName = true; 

//Create the query
var queryCustomers = from c in db.Customers 
    where (ignoreFirstName || (c.ContactFirstName.Contains("BlackListed")))
    where (ignoreLastName || (c.ContactLastName.Contains("BlackListed")))
    where (ignoreAddress || (c.Address.Contains("BlackListed"))
    select j;  

If ignoreFirstName is true in the query then the condition on the other side of the or statement will be ignored.

Answer 3

var query = from C in db.Customers select c;

if (seachFirstName)
         query = query.Where(c=>c.ContactFirstname.Contains("Blacklisted"));

if (seachLastName)
         query = query.Where(c=>c.ContactLastname.Contains("Blacklisted"));

if (seachAddress)
         query = query.Where(c=>c.Address.Contains("Blacklisted"));

Note that they aren't mutually exclusive.

Answer 4

Since this is not LINQ to Objects, but rather LINQ to SQL, you have no other alternative beside using either Expressions or a stored procedure.