Multiple MATCH works is incorrect

[mad]

Example of graph

        graph.traversal()
             .addV("Org").property("Name", "Org1").as("org1")
             .addV("Org").property("Name", "Org2").as("org2")
             .addV("Person").property("Name", "Foo").as("p1")
             .addV("Person").property("Name", "Boo").as("p2")
             .addV("Doc").property("Title", "Doc1").as("doc")
             .addE("E").from("org1").to("p1")
             .addE("E").from("org1").to("p2")
             .addE("E").from("org2").to("p1")
             .addE("E").from("org2").to("p2")
             .addE("E").from("org1").to("doc")
             .addE("E").from("org2").to("doc")

And cypher query

MATCH (org1:Org)--(p:Person)--(org2:Org)
MATCH (org1:Org)--(doc:Doc)--(org2:Org)
WHERE id(org1) IN [{nID}] AND id(org1) <> id(org2)
RETURN p.Name AS personName, org2.Name AS orgName

Expected result is:

[{personName=Boo, orgName=Org2}, {personName=Foo, orgName=Org2}]

But actual is:

[{personName=Foo, orgName=Org2}]

[dwitry]

Hello @mad,

thank you for reporting this.

As Cypher query is translated to a single Gremlin traversal, there are some limitations for multiple MATCH clauses. First MATCH clause returns 2 records. Second MATCH clause returns 1 record. As these are in the same traversal, result count gets limited by the second clause, and only 1st record is returned (query will work correctly if MATCH clauses are swapped).

You are right, this should be improved, but currently, I can't think of better translation for this case.

[mad]

Hello @dwitry

I think multiple match should be prevent for avoid bugs until new translation method introduced

[dwitry]

Hello @mad,

Agree, it makes sense to throw an exception on multiple MATCH clauses instead of returning an incorrect result. However, there are a lot of cases where multiple MATCH queries work as expected, for example:

MATCH (m:person {name: "marko"})
MATCH (m:person {age: 29})
MATCH (m:person)-[r1:created]->(lop:software {name: "lop"})
RETURN m

I will take a look if it is possible to distinguish queries that will provide an incorrect result.

[dwitry]

Hello @mad,

actually, I was wrong about multiple MATCH. Multiple MATCH feature is working correctly. The actual cause of this bug was incorrect handling of undirected paths.

Fix pushed to master and tinkerpop334.