But you're not asking to sort on /people/person/date_of_birth, you're asking to sort on that long nested expression which goes through multiple intermediary nodes, some of which can appear multiple times (as indicated by the [] array notation). It's this multiplicity that MQL is complaining about.
To fix it, take your query, paste it into the query editor, click on the innermost /person/date_of_birth and then click "Invert Query." That will turn the query inside out and give you something that looks like this:
[{
"name": [],
"/people/person/date_of_birth": [],
"type": "/tv/tv_actor",
"!/tv/regular_tv_appearance/actor": [{
"!/tv/tv_program/regular_cast": [{
"id": "/m/0524b41",
"name": [],
"sort": "/tv/tv_program/regular_cast./tv/regular_tv_appearance/actor./people/person/date_of_birth"
}]
}]
}]
which isn't exactly what you want, but indicates the general shape of your target query.
Getting rid of the array brackets for single valued properties and moving the sort clause to the outside gives us:
[{
"name": null,
"/people/person/date_of_birth": null,
"sort": "/people/person/date_of_birth",
"type": "/tv/tv_actor",
"!/tv/regular_tv_appearance/actor": [{
"!/tv/tv_program/regular_cast": [{
"id": "/m/0524b41",
"name": null
}]
}]
}]
which is functional and returns our 81 regular Game of Thrones actors sorted by birth date, but could still be cleaned up a bit more. The !inverse property notation isn't necessary since we have forward equivalents and we don't really need to get the Game of Thrones info over and over again since it's constant and we really just want to use it as a filter.
Incorporating these final tweaks gives us a final query like this which returns nice compact results:
[{
"name": null,
"/people/person/date_of_birth": null,
"sort": "/people/person/date_of_birth",
"type": "/tv/tv_actor",
"starring_roles": [{
"series": {
"id": "/m/0524b41"
},
"limit": 0
}]
}]
The "limit": 0 clause is a little trick to cause MQL to use that subquery for filtering, but not bother returning any of the (constant) information in the results. The /tv/tv_actor/starring_roles and /tv/regular_tv_appearance/series can be abbreviated to the simple property names because their types are implied by their context.
Since there are only 81 results, MQL's default limit of 100 is plenty and we don't need to worry about increasing it or using cursors.
Oldest Game of Thrones actor: Peter Vaughn, born 1923.
Youngest: Lino Facioli b. 2000
Note that 7 actors don't have birth dates in Freebase, so we don't know where they rank age-wise. Here's a bonus query which returns their names and ids as well as their character's name. If we were running a production system, we might use something like this to feed a human curation queue to fill in the gaps.
[{
"name": null,
"/people/person/date_of_birth": {
"value": null,
"optional": "forbidden"
},
"type": "/tv/tv_actor",
"starring_roles": [{
"series": {
"id": "/m/0524b41"
},
"character":null
}]
}]
The seven character/actor pairs are (were): Roose Bolton - Michael McElhatton,
Gregor Clegane - Conan Stevens,
Hizdahr zo Loraq - Joel Fry,
Rickon Stark - Art Parkinson,
Janos Slynt - Dominic Carter,
Hodor - Kristian Nairn,
Tommen Baratheon - Callum Wharry. I say "were" because I couldn't resist fixing Hodor's birth date. The strange thing is that it was in Wikipedia, so should have been picked up automatically by Freebase. I think there's a bug lurking there somewhere.
