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The Comparator::getInverse that inverts a comparator looks like

...
case LT: return GT;

case GT: return LT;

case LTE: return GTE;

case GTE: return LTE;
....

However, the inverse of LT should be GTE and similarly the other inverses (GT ->LTE, LTE->GT, GTE->LT).

For MATCH (n) or MATCH ()-[e]->() the parser produces the predicates n.__label__ = 'DefaultVertexLabel' and e.__label__ = 'DefaultEdgeLabel' which is not the expected behaviour

key = 1 -> Integer
key = 1L -> Long

for e.g. MATCH (v) WHERE v.__label__ = "Foo" the label needs to be updated at the query vertex representing v.

Queries conjoining a NOT predicate are not handled correctly.
E.g., the query
MATCH (alice)-[r]->(bob) WHERE bob.age<30 AND NOT alice.age > 50
yields the predicate
(alice.age > 50 AND (NOT bob.age < 30))
in GDLLoader.java.

I think this is due to confusion of FIFO/LIFO functionality in GDLLoader::exitNotExpression
Changing line 561 in GDLLoader.java from

Predicate not = new Not(currentPredicates.pop());

to

Predicate not = new Not(currentPredicates.removeLast());

fixed this issue for me, test cases still worked after this change.

In Order to be able to match certain ID we have to be able to specify GradoopIDs inside a query

I would suggest the following markup

MATCH (a)
WHERE a = GradoopId(0000-0000-00-000)
RETURN

Would fix opencypher/morpheus#143

Would be great to reduce the necessary configuration overhead to use GDL by adding it to the maven central instead of our "special" solution as we discussed it in our gradoop-team-meeting.

In a project were we're implementing Cypher we're using GDL to generate test graphs. In order to test whether a GDL-defined graph is identical to a graph generated by our system, we need to control what ids entities in GDL are given.

It would be lovely to support some kind of injection of an id-generator interface, or similar, which we can use to position the id generator in the correct state for our test case.

Once Gradoop supports it, GDL should be able to parse Date and DateTime property values.
Gradoop issue dbs-leipzig/gradoop#488
E.g.

WHERE a.birthday > 01.01.1991

Related to dbs-leipzig/gradoop#1482

We should support alternate labels in the MATCH clause

E.g.

MATCH (me:Person|:Alien)
RETURN me

Which is equal to

MATCH (me)
WHERE me.__label__ = "Person" OR me.__label__ = "Alien"
RETURN me

e.g.:

String gdlString = "(alice:Person)-e->(:Person)";
GDLHandler gdlHandler = new GDLHandler.Builder().buildFromString(gdlString);
for (Vertex v : gdlHandler.getVertices()) {
  System.out.println(v.getVariable());
}

output:

alice
null

We currently use != for not equal. However, Cypher uses <>, hence we should support both?

MATCH ()-->()

loader.getEdges().stream().findFirst().get().hasVariableLength() returns true

E.g. (u1 {score: 1.0}), (u1 {score: 2.0}) shouldn't be valid, as most likely it is a copy-paste error.
In another sense, this is actually trying to guess the users intent. Maybe a warning would also a solution.

From a compiler point of view, this is the equivalent of:

a = 10;
a = 12;

Co-issued: @breakanalysis

key = 1.0 -> Float
key = 1.0d -> Double

In Cypher nodes can have zero or more labels, and it would be nice to have support for that.

It seems that all special characters are prohibited in vertex and edge labels.
Is there a reason why?
I think a blacklist of reserved characters would be sufficient.

Currently the ANTLR parser uses the default error strategy org.antlr.v4.runtime.DefaultErrorStrategy which just prints to the standard error for each parse error but continues the parsing. The user has no way of knowing/reacting to syntax errors.
If there was a way of specifying an alternative error strategy, for example org.antlr.v4.runtime.BailErrorStrategy via org.antlr.v4.runtime.Parser.setErrorHandler(ANTLRErrorStrategy) the user could choose to wrap the parser in a try/catch-block an catch org.antlr.v4.runtime.misc.ParseCancellationException.ParseCancellationException(Throwable).

Usually, a user would expect the GDL reader to throw an exception in case off the input not matching the correct GDL syntax. The DefaultErrorStrategy only prints out the wrong syntax while the BailErrorStrategy only throws an exception without printing that false input.
An additional ErrorStrategy printing out syntax errors and throwing exceptions would be helpful.

Instead of using thridparty travis ci for integration testing we can use the provided github actions to trigger testing with maven.

The Neo4j Cypher default for edge labels (or types) is upper-case snake-case, e.g., :WORKS_AT.
Currently this is not supported by GDL

1.0$ -> BigDecimal