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opengeospatial / sensorthings

The official web site of the OGC SensorThings API standard specification.
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Filter on empty geometry feature, empty object, or non-existing property #109

Open matcho opened 3 years ago

matcho commented 3 years ago

Hello,

We have a set of FeaturesOfInterest, some of them are geolocated and others are not. In the latter case, the feature property is an empty object {} which satisfies the mandatory nature of the property.

Now we're trying to obtain the list of non-geolocated FeaturesOfInterest.

Is it possible to filter on "empty geometry feature", as does PostGIS st_isempty() function ?

Otherwise, is it possible to filter on "empty object", for ex. with something that could look like $filter=feature eq {} or $filter=empty(feature) ?

In an even more general way, is it possible to filter on "non-existing property" or "null property", for ex. $filter=feature/type eq NULL or $filter=not has_property(feature/type) ?

Or is there another way to achieve such queries with other semantics ?

Thank you for any advice, Mathias

hylkevds commented 3 years ago

An explicit check for null would be nice. One thing that comes to mind that should already work is using the length() function to check the contents of the field:

    /v1.1/FeaturesOfInterest?$filter=length(feature) lt 5
hylkevds commented 3 years ago

Also, since the feature field has type ANY, you can also use an empty string as feature stead of {}. and you could set the encodingType to "none", then you can filter on that.

matcho commented 3 years ago

Thank you, filtering on length(feature) lt 5 works well and fast.