Grails criteria query retruing duplicate instances

Question

I have a domain class called Order and that class has hasMany relation with Item class. When I am querying for the list of orders with certain restrictions I am getting as many instances of Order as there are items.

So for example Order instance has say references to 3 instances of Item then , criteria call on Order is returning 3 duplicate instances of Order. I am not sure but if it's worth mentioning that the domain class Order has fetchMode set to "eager".

I am really puzzled with what's going on there. Any help in this regard will be greatly appreciated. Snippet of code is attached:

def clazz = "cust.Order"
def criteria = clazz.createCriteria()
        println("clazz == "+Order.list())// returning correct data i.e unique instance of order
        def filter = {
                    // trimmed down all filtering criteria for debugging
            }//close filter
        List results = criteria.list(max:params?.max,offset:params?.offset,filter)
            results.each{Object data->
                println(data.getClass())
            }
        println("results == "+results)

Thanks again

Answer 1

Criteria API is just a wrapper for constructing a SQL query. In your case, the query in question has JOINs in it (because of the eager fetching), and returns a cartesian product of Orders and their matching Items. Each row returned is included in results as a separate Order instance.

The easiest way to remove duplicates is to put all the results in a Set, like this:

def resultSet = new HashSet()
resultSet.addAll(results)
println("results == " + resultSet)