Dynamic Where condition with Queryover

Question

I have an application and I'm trying to implement DDD concepts. I have my repository class with some method to list entities. I would like to know how can I do a query with QueryOver to filter separating with AND operator, when the parameter is filled, sample

public IEnumerable<Product> FindProducts(string name, decimal? price, DateTime? validDate, int? stock, int? idSupplier)
{
   var query = Session.QueryOver<Product>().OrderBy(x => x.Name).Asc;

   if (!string.IsNullOrEmpty(name))
      // add where condition for name parameter

   if (price.HasValue)
      // add 'AND' where condition for price parameter

   if (validDate.HasValue)
      // add 'AND' where condition for validDate parameter

   if (idSupplier.HasValue)
      // add 'AND' where condition for idSupplier parameter

   // other possible conditions

   return query.List();
}

Is there any way to do that before I use HQL string query? hehehe

Thank you!

Barri

Answer 1

Here, use PredicateBuilder:

How To:

IQueryable<Product> SearchProducts (params string[] keywords)
{
  var predicate = PredicateBuilder.False<Product>();

  foreach (string keyword in keywords)
  {
    string temp = keyword;
    predicate = predicate.Or (p => p.Description.Contains (temp));
  }
  return dataContext.Products.Where (predicate);
}

PredicateBuilder Source:

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);
  }
}

For more information on PredicateBuilder and LinqKit go here: http://www.albahari.com/nutshell/linqkit.aspx

Orvah

Yes I know i can do the second way, bu how can I add other possible conditions in it? – Barri

@felipeoriani read up on predicate builder, assuming you're OK with a 3rd party lib (a lot of people use it, it's safe ;-), then I'd use that. – Orvah

Great code, I will try it , thanks :)... I didn't know this lib, where can I find it? Thanks []s – Barri

Just use the code I put here, use it in your own solution. The lib itself is just this code. You can reference it, or include it in your own project so you can manipulate it easier! Also, don't forget to upvote/mark as answer ;) More information on PredicateBuilder is available here: albahari.com/nutshell/predicatebuilder.aspx – Orvah

More information on PredicateBuilder - albahari.com/nutshell/predicatebuilder.aspx More usage examples and whatnot – Orvah

Thanks man, only one more question, can I integrate it with QueryOver of Nhibernate, I mean, how can I do a condition using 'like' operation? thanks for the link! – Barri

Type out some code in the way you would EXPECT it to work and I'll be happy to take a look. But right now I'm not sure I understand your question! ;) – Orvah