Multiple WHERE Clauses with LINQ extension methods

Question

I have a LINQ query that looks like the following   DateTime today   DateTime UtcNow  var results   from order in context Orders               where   order OrderDate  lt   today   amp  amp   today  lt   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   gt  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

User · Answer

you can use  amp  amp  and write all conditions in to the same where clause  or you can  Where   Where   Where      and so on

User · Answer

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 lt YourDataClass gt      if  condition1        predicate   predicate Or d   gt  d SomeStringProperty     Tom       if  condition2        predicate   predicate Or d   gt  d SomeStringProperty     Alex       if  condition3        predicate   predicate And d   gt  d SomeIntProperty  gt   4      return originalCollection Where lt YourDataClass gt  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 lt Func lt T  bool gt  gt  True lt T gt        return f   gt  true       public static Expression lt Func lt T  bool gt  gt  False lt T gt       return f   gt  false       public static Expression lt Func lt T  bool gt  gt  Or lt T gt   this Expression lt Func lt T  bool gt  gt  expr1                                                        Expression lt Func lt T  bool gt  gt  expr2          var invokedExpr   Expression Invoke  expr2  expr1 Parameters Cast lt Expression gt           return Expression Lambda lt Func lt T  bool gt  gt             Expression OrElse  expr1 Body  invokedExpr   expr1 Parameters          public static Expression lt Func lt T  bool gt  gt  And lt T gt   this Expression lt Func lt T  bool gt  gt  expr1                                                         Expression lt Func lt T  bool gt  gt  expr2          var invokedExpr   Expression Invoke  expr2  expr1 Parameters Cast lt Expression gt           return Expression Lambda lt Func lt T  bool gt  gt             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

User · Answer

Two ways   results   results Where o   gt   o OrderStatus    OrderStatus Open   amp  amp                                o CustomerID    customerID      or   results   results Where o   gt   o OrderStatus    OrderStatus Open                     Where o   gt   o CustomerID    customerID      I usually prefer the latter   But it s worth profiling the SQL server to check the query execution and see which one performs better for your data  if there s any difference at all    A note about chaining the  Where   methods   You can chain together all the LINQ methods you want   Methods like  Where   don t actually execute against the database  yet    They defer execution until the actual results are calculated  such as with a  Count   or a  ToList      So  as you chain together multiple methods  more calls to  Where    maybe an  OrderBy   or something to that effect  etc   they build up what s called an expression tree   This entire tree is what gets executed against the data source when the time comes to evaluate it

User · Answer

results   context Orders Where o   gt  o OrderDate  lt   today  amp  amp  today  lt   o OrderDate    The select is uneeded as you are already working with an order

User · Answer

Just use the  amp  amp  operator like you would with any other statement that you need to do boolean logic   if  useAdditionalClauses      results   results Where                    o   gt  o OrderStatus    OrderStatus Open                     amp  amp  o CustomerID    customerID

User · Answer

Surely   if  useAdditionalClauses        results        results Where o   gt  o OrderStatus    OrderStatus Open  amp  amp       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   gt  o OrderStatus    OrderStatus Open       Where o   gt  o CustomerID    customerID        Or another reassignment to results   results   results Where blah

User · Answer

You can continue chaining them like you ve done   results   results Where  o   gt  o OrderStatus    OrderStatus Open   results   results Where  o   gt  o InvoicePaid     This represents an AND

[c#] Multiple WHERE Clauses with LINQ extension methods

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