[FREEMARKER-61] ?sort_using with a Comparator parameter

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.3.26-incubating
• Component/s: engine
• Assignee: Unassigned
• Reporter: Ondra Žižka
• Created: 11/Jul/17 13:54
• Updated: 13/Jul/17 02:48

Description

Hi Daniel

I know that lists should be sorted before passing them to the template in general.
In our case, the template is backed by a generic API for graph database which gives an Iterable for any 1:N relation. So sorting needs to happen in the template.

Now I'd like to sort that, for which the ?sort_by(["...", "..."]) is good enough, except when it gets a bit more complicated - e.g. sometimes the values are missing in which case it should sort by something else...

Doing that in a template is not a good idea, so I suggest this, elegant in my opinion, solution:
First you'd have a Comparator in Java, and perhaps register it like you do with FreemarkerMethod.
Then you could pass this as a parameter to ?sort_using.

public class SortByName implements Comparator { ... }

myData.persons?sort_using("SortByName")

This would be even better if it could pass parameters to the constructor:

public class SortByName implements Comparator {
    public SortByName(boolean ladiesFirst) { ... }
}

myData.persons?sort_using("SortByName", [true])

This would greatly leverage sorting in templates while not complicating the template syntax or cluttering ?sort_by.

Thanks for considering.