Query: Parsing collect() results sometimes fails

[johannessen]

Hi Mark,

I discovered REST::Neo4p is unable to parse the result of certain Cypher queries that use expressions calling Neo4j functions like collect() in the RETURN clause. Minimized example:

# set up graph for testing
my $q1 = REST::Neo4p::Query->new(<<END);
CREATE (a:Test)-[:TEST{test:true}]->(:Test)
RETURN id(a)
END
$q1->execute();
my $id = $q1->fetch->[0];

# test collecting properties that are undefined
my $q2 = REST::Neo4p::Query->new(<<END);
MATCH (p:Test)-[r]-(o) WHERE id(p) = {id}
RETURN collect(r.void)
END
$q2->execute(id => $id);
print Dumper $q2->fetch->[0];  # expected: []
# dies: Can't use an undefined value as an ARRAY reference at REST/Neo4p/Query.pm line 428.

# test collecting properties that have boolean values
my $q3 = REST::Neo4p::Query->new(<<END);
MATCH (p:Test)-[r]-(o) WHERE id(p) = {id}
RETURN collect(r.test)
END
$q3->execute(id => $id);
print Dumper $q3->fetch->[0];  # expected: [true]
# dies: Not a HASH reference at REST/Neo4p/Query.pm line 358.

This issue is reproducible for REST::Neo4p 0.3020 with Neo4j versions 2.3.3, 3.0.0 and 3.3.5.

I worked around this issue by simplifying my queries, so I don’t need a fix at this time. But I still wanted to document it.

Furthermore I clearly remember having similar problems with the substring() function. Which is quite mystifying since producing a simple string is of course all it does, and I fail to see why e. g. substring('1999-12-31', 0, 4) would fail where '1999' succeeds. However, I now seem to be unable to reproduce this issue, so I suppose it’s not just possible, but in fact probable I simply made a mistake of some sort there.

Cheers,
Arne

[majensen]

@johannessen this is a great bug, and I'll fix it and add a test-- hopefully soon.
Mark

[majensen]

Probably still need to fix this!

[johannessen]

Running the example code above with the default agent reveals the following:

• collect(r.void) no longer dies, but still returns undef (it's supposed to return an empty array ref [])
• collect(r.test) still dies with the same message Not a HASH reference

But given that this issue is indeed not reproducible with the Neo4j::Driver agent, an easy solution might be to eventually make Neo4j::Driver the default agent.