Motivation: |
X-path expressions can return multiple values. Comparison operators on values (=, <, >, etc) and geometries (overlaps, intersects, etc...) in the filters currently do not handle multiple values as input. |
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Contact: |
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Tracker: |
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Tagline: |
filter x-path |
This page represents the current plan; for discussion please check the tracker link above.
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Children: |
Description
The proposal is to modify the following filters:
- comparison filters: equals, not equals, gt, gte, lt, lte, between, like
- all geometry filters
To allow collections of values as input, besides single values. if an expression returns a collection of values rather than just a single value, the filters will be able to handle it. The OGC Filter standard specifies that the way to deal with multiple values can be modified using the "matchAction" flag:
7.7.3.3
matchAction parameter
The matchAction attribute can be used to specify how the comparison predicate shall be evaluated for a
collection of values (e.g. in XML, properties having maxOccurs > 1) and not including some additional context
to identify a specific value from the collection to be tested. Possible values for the attribute are: All, Any or
One. A value of All means that all values in the collection shall satisfy the predicate. A value of Any means
that any of the value in the collection can satisfy the predicate. Finally, a value of One means that only one of
the values in the collection shall satisfy the predicate.
If the value of the matchAction attribute is One, additional context (e.g. XPath index) can be included to
indicate which value in the collection should satisfy the predicate.
EXAMPLE
The following example illustrates the use of the matchAction attribute. Consider the following XML
fragment, which is an instance of a GML (see ISO 19136) feature:
And consider the following filter expression:
If the value of the matchAction attribute is set to Any, this predicate will evaluate to true since there is at least
one gml:name value that satisfied the predicate. If the value of the matchAction attribute is All, this predicate
will evaluate to false since not all gml:name values are Flatiron. Finally, if the matchAction attribute is set to
One then the expression will evaluate to true since only one gml:name value is Flatiron.
If the value of the matchAction attribute is Any or All, the ValueReference XPath expression shall not include
an index predicate. If the matchAction attribute is One an XPath index predicate may be specified and the
predicate shall only evaluate to true if not only one value matches the predicate but the specific value
indicates by the index matches the value.
The default value of "matchAction" is "Any" i.e. the result will be the OR-ed aggregation of all possible combinations. For example, if we compare the following values
(x, y, z) = (a, b)
the result will be true if x=a OR x=b OR y=a OR y=b OR z=a OR z=b.
Plan
MatchAction
The plan is to introduce an Enum MatchAction for ANY, ALL, ONE.
Update Filter with getMatchAction() methods
The update is limited to:
- BinaryComparisonOperator
- PropertyIsBetween
- PropertyisLike
- SpatialOperator
Update FilterFactory
Update FilterFactory and FilterFactory2 interfaces to allow MatchAction to be supplied.
For reference here is a code example showing how things stand:
The idea is to explicitly allow for MatchCase enumeration:
Update Filter implementations
Inside the implementation of equals we will need to update the code to expect a List of values (rather than a single value).
Here is an example of how any filter implementation can be made compatible with multiple values:
Status
Proposal accepted, work is proceeding on the 8.x branch:
- Andrea Aime +1
- Ben Caradoc-Davies: +1
- Christian Mueller +0
- Ian Turton +1
- Justin Deoliveira +1
- Jody Garnett +1
- Simone Giannecchini +0
Tasks
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no progress |
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done |
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impeded |
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lack mandate/funds/time |
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volunteer needed |
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NC: Modify filter implementation to work with default "ANY" implementation + add unit tests for new behaviour- NC: Check for any effects on other modules like gt-render
- NC: Update Filter interface to retrieve "matchAction" property (default: MatchAction.ANY)
- NC: Update Filter implementation to deal with MatchAction.ALL and MatchAction.ANY properties for MatchAction.
- NC: Update Filter factories to create filters with customised "matchAction" properties
- JD: Update XML parser to parse the 'matchAction' property.
: Review user documentation for changes
- http://docs.geotools.org/latest/userguide/library/main/filter.html
- http://docs.geotools.org/latest/userguide/library/opengis/filter.html
- Update pictures in images/ folder using ObjectAID eclipse plugin
- bonus: add example for matchCase since that was not done
API Changes
FilterFactory
BEFORE:
AFTER:
(This is done for any filter that supports matchAction).
Filters
BEFORE:
AFTER:
(The same is done for PropertyIsBetween, PropertyIsLike and SpatialOperator )
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