Divij Vaidya created TINKERPOP-2710:
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Summary: hasKey() should throw an error when invoked on Elements
Key: TINKERPOP-2710
URL: https://issues.apache.org/jira/browse/TINKERPOP-2710
Project: TinkerPop
Issue Type: Bug
Components: language
Affects Versions: 3.6.0
Reporter: Divij Vaidya
Fix For: 3.6.0
*Context*
hasKey() step can be added to the traversal when the traverser is of type
Element or when it is of type Property.
When step is invoked for traverser of type property, the behaviour is well
defined as, "Remove the {{Property}} traverser if it does not match one of the
provided keys." Example query:
{noformat}
gremlin> g.V().properties().hasKey('age').value()
==>29
==>27
==>32
==>35{noformat}
When the step is invoked for traverser of type Element, the behaviour of the
step is not documented. [Looking at the
code|https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/HasContainer.java#L59]
implementation, it "removes the element traverser if element has a property
with key as '~key' and the value of that property matches 'age'".
But [this condition is
unsatisfiable|https://github.com/apache/tinkerpop/blob/6a0b71b2af79b1b45f1e2db41946fe85529ed32e/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/ElementHelper.java#L84]
because Element can never have a property with key "~key". It would fail at
insertion.
*Change proposed*
Hence, I propose the following change:
If hasKey() is applied to a traverser of Element type, then it should throw an
error.
The code change will be made
[here|https://github.com/apache/tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/HasContainer.java#L59]
. We would introduce a change as follows:
{noformat}
if (this.key.equals(T.key.getAccessor())) {
throw new IllegalArgumentException("hasKey() cannot be applied to traverser
of type Element")
}{noformat}
*Impact of the change*
Before the change:
{noformat}
// the following query always returns empty results
g.V().hasKey('age'){noformat}
After the change:
{noformat}
// the following query returns an error
gremlin> g.V().hasKey('age')
hasKey() cannot be applied to traverser of type Element{noformat}
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