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https://issues.apache.org/jira/browse/TINKERPOP-2727?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17514658#comment-17514658
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ASF GitHub Bot commented on TINKERPOP-2727:
-------------------------------------------
FlorianHockmann commented on a change in pull request #1596:
URL: https://github.com/apache/tinkerpop/pull/1596#discussion_r838467234
##########
File path: docs/src/reference/the-traversal.asciidoc
##########
@@ -1434,6 +1436,15 @@ the key,value pairs for those vertices.
<6> Find all age-properties and emit their value.
<7> Find all vertices that do not have an age-property and emit their name.
<8> Find all "person" vertices that have a name property that starts with the
letter "m".
+<9> Property key values cannot be `null` and therefore produces no matches.
Review comment:
Not that important, but _produce_ without an _s_, right?
##########
File path: docs/src/reference/the-traversal.asciidoc
##########
@@ -1434,6 +1436,15 @@ the key,value pairs for those vertices.
<6> Find all age-properties and emit their value.
<7> Find all vertices that do not have an age-property and emit their name.
<8> Find all "person" vertices that have a name property that starts with the
letter "m".
+<9> Property key values cannot be `null` and therefore produces no matches.
+<10> An example of `has()` where the argument is a `Traversal` and does not
quite behave the way most expect.
+
+Item 10 in the above set of examples bears some discussion. The behavior is
not such that the result of the `Traversal`
+is used as the comparing value for `has()`, but the current `Traverser`, which
in this case is the vertex `label`, is
+given to the `Traversal` to behave as a filter itself. In other words, if the
`Traversal` (i.e. `is('person')`) returns
+a value then the `has()` is effectively `true`. A common mistake is to try to
use `select()` in this context where one
+would do `has('name', select('n'))` to try to inject the value of "n" into the
step to get `has('name', <value-of-n>)`,
Review comment:
Oh wow, good explanation. I expected `has()` to behave this way with the
`is()` step, but I would also have expected it to work with `select()` like you
described here. Good to know!
##########
File path: gremlin-test/features/filter/Has.feature
##########
@@ -804,6 +813,48 @@ Feature: Step - has()
When iterated to list
Then the result should be empty
+ Scenario: g_V_hasXlabel_personX
+ Given the modern graph
+ And the traversal of
+ """
+ g.V().has(T.label, "person")
+ """
+ When iterated to list
+ Then the result should be unordered
+ | result |
+ | v[marko] |
+ | v[vadas] |
+ | v[josh] |
+ | v[peter] |
+
+ Scenario: g_V_hasXlabel_eqXpersonXX
+ Given the modern graph
+ And the traversal of
+ """
+ g.V().has(T.label, eq("person"))
+ """
+ When iterated to list
+ Then the result should be unordered
+ | result |
+ | v[marko] |
+ | v[vadas] |
+ | v[josh] |
+ | v[peter] |
+
+ Scenario: g_V_hasXlabel_constantXpersonXX
Review comment:
Shouldn't this be named `g_V_hasXlabel_isXpersonXX`?
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> HasContainer should allow a null key
> ------------------------------------
>
> Key: TINKERPOP-2727
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2727
> Project: TinkerPop
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.5.2
> Reporter: Florian Hockmann
> Priority: Minor
>
> TINKERPOP-2605 changed {{null}} semantics to allow {{null}} as an argument in
> more places so that {{has(null)}} should not throw a NPE any more and instead
> filter all traversers out.
> {{HasContainer}} however still throws a NPE if the {{key}} is {{{}null{}}}.
> I discovered this when trying to update JanusGraph [as that folds in a
> {{HasContainer}} like
> this|https://github.com/JanusGraph/janusgraph/blob/4246d49cee46d549d752515f3956cd2d59f1fd0a/janusgraph-core/src/main/java/org/janusgraph/graphdb/tinkerpop/optimize/step/HasStepFolder.java#L266]
> which leads to the NPE and thus failing tests.
> The same behavior can also be produced with just TinkerGraph and for example
> the following traversals:
> {code:java}
> g.V().has(null, 1)
> g.V().has(null, P.neq(null)){code}
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