[Developers] query for values vs name/id

[Tim Sturge]

The shortcut:

"/music/artist/active_start": [{}]

The explanation:

There's a bit of a trick to this. MQL divides the world into "values" 
and "objects". If you look at the expected_type of a property (try the query

{ "query0":
{ "query":
{ "id": "<a-property-like-/music/artist/active_start>",
"type": "/type/property",
"expected_type": null
}
}
}

You will find out if a property expects a value (one of /type/id, 
/type/key, /type/text, /type/rawstring, /type/int, /type/float, 
/type/boolean and /type/uri) or an object (anything else)

Then you can ask

[{ "name": null, "id": null, "type": [], "optional": true }]

for the objects and

[{ "value": null, "type": null, "optional": true }]

for the values. (the optional: true ensures the query doesn't fail if 
the property is missing)

[{}]

asks MQL to automatically inspect the expected_type for you and insert 
one or other of the clauses you see above, depending on which is 
appropriate. It's what we use internally 90% of the time.

Tim

Steve Sak wrote:
> Given that I've performed a query to get the properties of some class,
> say /music/artist and now want to get the "values" and maybe some other
> attributes of those properties what does the query look like?  The
> problem I'm running into is when asking for attributes explicitly I
> can't tell if the property refers to a primitive attibute or another
> object.  Perhaps I'm just missing something obvious.
>
> For instance:
>
> {"query0": { "query":[{
> "limit":1,
> "name":"The Police",
> "type":"/music/artist",
> "/music/artist/active_start":[{"name":null,"id":null}],
> "/music/artist/acquire_webpage":[{"name":null,"id":null}],
> "/music/artist/album":[{"name":null,"id":null}],
> "/music/artist/similar_artist":[{"name":null,"id":null}],
> "/music/artist/origin":[{"name":null,"id":null}],
> "/music/artist/home_page":[{"name":null,"id":null}],
> "/music/artist/active_end":[{"name":null,"id":null}],
> "/music/artist/label":[{"name":null,"id":null}],
> "/music/artist/artist_similar":[{"name":null,"id":null}],"
> /music/artist/genre":[{"name":null,"id":null}],
> "/music/artist/track":[{"name":null,"id":null}],
> "/music/artist/contribution":[{"name":null,"id":null}],
> "/music/artist/member":[{"name":null,"id":null}]}]}}
>
> gives the error:
>
> {
>    "status": "/mql/status/error",
>    "messages": [   {
>       "info":       {
>          "property": "name",
>          "expected_type": "/type/datetime"
>       },
>       "query": [      {
>          "/music/artist/active_start": [         {
>             "error_inside": ".",
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/acquire_webpage": [         {
>             "name": null,
>             "id": null
>          }],
>          "limit": 1,
>          "type": "/music/artist",
>          "/music/artist/album": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/similar_artist": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/home_page": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/origin": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/active_end": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/label": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/genre": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/artist_similar": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/track": [         {
>             "name": null,
>             "id": null
>          }],
>          "/music/artist/contribution": [         {
>             "name": null,
>             "id": null
>          }],
>          "name": "The Police",
>          "/music/artist/member": [         {
>             "name": null,
>             "id": null
>          }]
>       }],
>       "type": "/mql/error",
>       "message": "Type /type/datetime does not have property name",
>       "path": "/music/artist/active_start",
>       "status": "/mql/status/type_error"
>    }]
> }
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