[jira] [Comment Edited] (TINKERPOP-2710) hasKey() should throw an error when invoked on Elements

["Dave Bechberger (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TINKERPOP-2710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17508546#comment-17508546 ] 

Dave Bechberger edited comment on TINKERPOP-2710 at 3/18/22, 3:20 AM:
----------------------------------------------------------------------

I am generally against throwing errors when if the intent of the query is able to be determined as errors generally lead to a lot more undifferentiated work for a consumer to manage.. 

 

Given the query

```

g.V().hasKey('age').fold()

```

It seems to be that the intent of this query is to find all the vertices with a key of `age` which seems equivalent to `g.V().has('age')` and return the elements with the key.

 

```

gremlin> g.V().has('age')
==>v[1]
==>v[2]
==>v[4]
==>v[6]

```

This would also be a breaking change but would lead to fewer errors being thrown and greater consistency among seemingly identical steps.


was (Author: bechbd):
I am generally against throwing errors when if the intent of the query is able to be determined as errors generally lead to a lot more undifferentiated work for a consumer to manage.. 

 

Given the query

```

g.V().hasKey('age').fold()

```

It seems to be that the intent of this query is that an user wants to find all the vertices with a key of `age` which seems equivalent to `g.V().has('age')` and return the elements with the key.

 

```

gremlin> g.V().has('age')
==>v[1]
==>v[2]
==>v[4]
==>v[6]

```

This would also be a breaking change but would lead to fewer errors being thrown and greater consistency among seemingly identical steps.

> 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, process
>    Affects Versions: 3.6.0
>            Reporter: Divij Vaidya
>            Priority: Major
>
> *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 always fail at insertion i.e. the output of hasKey() on Element traverser will always be empty.
> *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  gremlin> g.V().hasKey('age').fold() 
> gremlin> g.V().hasKey('age').fold()
> ==>[]{noformat}
>  
> After the change:
> {noformat}
> // the following query returns an error
> gremlin> g.V().hasKey('age').fold()
> hasKey() cannot be applied to traverser of type Element{noformat}
>  
>  
>  



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