[c#] Multiple WHERE Clauses with LINQ extension methods

I have a LINQ query that looks like the following:

DateTime today = DateTime.UtcNow;
var results = from order in context.Orders
              where ((order.OrderDate <= today) && (today <= order.OrderDate))
              select order;

I am trying to learn / understand LINQ. In some cases, I need to add two additional WHERE clauses. In an effort to do this, I'm using:

if (useAdditionalClauses)
{
  results = results.Where(o => o.OrderStatus == OrderStatus.Open)  // Now I'm stuck.
}

As you can see, I know how to add an additional WHERE clause. But how do I add multiple? For instance, I'd like to add

WHERE o.OrderStatus == OrderStatus.Open AND o.CustomerID == customerID

to my previous query. How do I do this using extension methods?

Thank you!

This question is related to c# linq

The answer is


Just use the && operator like you would with any other statement that you need to do boolean logic.

if (useAdditionalClauses)
{
  results = results.Where(
                  o => o.OrderStatus == OrderStatus.Open 
                  && o.CustomerID == customerID)     
}

results = context.Orders.Where(o => o.OrderDate <= today && today <= o.OrderDate)

The select is uneeded as you are already working with an order.


you can use && and write all conditions in to the same where clause, or you can .Where().Where().Where()... and so on.


If you working with in-memory data (read "collections of POCO") you may also stack your expressions together using PredicateBuilder like so:

// initial "false" condition just to start "OR" clause with
var predicate = PredicateBuilder.False<YourDataClass>();

if (condition1)
{
    predicate = predicate.Or(d => d.SomeStringProperty == "Tom");
}

if (condition2)
{
    predicate = predicate.Or(d => d.SomeStringProperty == "Alex");
}

if (condition3)
{
    predicate = predicate.And(d => d.SomeIntProperty >= 4);
}

return originalCollection.Where<YourDataClass>(predicate.Compile());

The full source of mentioned PredicateBuilder is bellow (but you could also check the original page with a few more examples):

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;

public static class PredicateBuilder
{
  public static Expression<Func<T, bool>> True<T> ()  { return f => true;  }
  public static Expression<Func<T, bool>> False<T> () { return f => false; }

  public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
                                                      Expression<Func<T, bool>> expr2)
  {
    var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
    return Expression.Lambda<Func<T, bool>>
          (Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
  }

  public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
                                                       Expression<Func<T, bool>> expr2)
  {
    var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
    return Expression.Lambda<Func<T, bool>>
          (Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
  }
}

Note: I've tested this approach with Portable Class Library project and have to use .Compile() to make it work:

Where(predicate .Compile() );


You can continue chaining them like you've done.

results = results.Where (o => o.OrderStatus == OrderStatus.Open);
results = results.Where (o => o.InvoicePaid);

This represents an AND.


Surely:

if (useAdditionalClauses) 
{ 
  results = 
    results.Where(o => o.OrderStatus == OrderStatus.Open && 
    o.CustomerID == customerID)  
} 

Or just another .Where() call like this one (although I don't know why you would want to, unless it's split by another boolean control variable):

if (useAdditionalClauses) 
{ 
  results = results.Where(o => o.OrderStatus == OrderStatus.Open).
    Where(o => o.CustomerID == customerID);
} 

Or another reassignment to results: `results = results.Where(blah).