JSON Serialization of Sets results in loss of order

Sets don't have order, use a List (http://grails.org/doc/latest/guide/GORM.html#sets,ListsAndMaps). This is not a bug, recommend closing. Thanks, Bobby

Technically there are no Sets in JSON, only Maps and Lists. The principle of least surprise would be to treat Sets as lists and respect the order of the Set. What is the harm in preserving the input order? What if the input set WAS a LinkedHashSet? The order that the user specified would be lost.

I'm either misunderstanding you or simply just not getting the problem... If you have your collection mapped as a List and render it as JSON, is the order not preserved? Why are you trying to use LinkedHashSet as opposed to just a List? What is the actual issue that using a List doesn't solve? Please let me know.

Thanks,
Bobby

Sorry if I'm not being clear.

From my example on the mailing list, you can see my two classes and their relation:

class Parent

class Child {

static belongsTo = [parent: Parent]

static mapping =

}

I did not map my collection as a List as I was unaware I needed to in order to get insertion sort ordering for my collection. From the rest of my application's perspective, the order is correct.
e.g.:
parent.children

returns a set of child Objects that are sorted by the order they were created (or something else, ID?) I'm not sure why the order is correct as I'm not implementing comparable or overriding hashCode anywhere in my domain objects.

I can declare my collection as a List in GORM, (although I can't really have any duplicates in practice) but this seems to be a weird artifact of how the JSON DomainClassMarshaller works. Its behavior is not consistent with the CollectionMarshaller, which just serializes the collection in order.

For example, calling:
parent.children as JSON
gives me the correct order.

Why does the DomainClassMarshaller go to great lengths to determine whether a set is sorted or not, when it could just preserve input order using a List and be done with it?

You could replace all of this code:

if (referenceObject instanceof SortedMap)

else if (referenceObject instanceof SortedSet)

else if (referenceObject instanceof Set)

else if (referenceObject instanceof Map)

else if (referenceObject instanceof Collection)

I left out a key detail from the example. The parent has a static mapping =

which explains why the children are sorted in the Parent Domain class.

If I were to declare children as a List, as you have pointed me to in the documentation:
http://grails.org/doc/latest/guide/GORM.html#sets,ListsAndMaps , I would need to declare an idx column in my child table to perform the sorting for the list. In my use case, I'm only reading data from the db, never adding new children and saving them, so perhaps that's why I'm not getting bitten by sorting problems in the domain. If I can get away with not adding this extra column to my child table, I would prefer to do so.

This issue ignores SortedSet, which should become a JSON array with the same order as the sorted set. I think using LinkedHashSet for the defensive copy is appropriate. It would maintain the order of both SortedSet and LinkedHashSet.