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!

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