How do I write a parameterised gremlin query to add a vertex with many number of properties. I want to parameterise the property in such a way that.. I should be able to pass the properties in a Map and the query to read and insert all those into the vertex. Is this possible at all?
It is only possible with a script where you construct the traversal on the remote side and, then, only possible for graph systems that support scripts in that way (e.g. wouldn't work on CosmosDB). You would just send your script as the following where m is your Map:
t = g.addV()
m.each{k,v -> t= t.property(k,v)]
t
Related
I'm trying to execute an OLAP traversal on a query that needs to check if a vertex has a neighbour of certain type.
i keep getting
Local traversals may not traverse past the local star-graph on GraphComputer
my query looks something like:
g.V().hasLabel('label1').
where(_.out().hasLable('label2'))
I'm using the TraversalVertexProgram.
needless to say, when running the same query in oltp mode there is no problem
is there a way to execute such logic?
That is limitation of TinkerPop OLAP GraphComputer. It operate on 'star-graph' objects. The vertex and connected edges only. It uses message passing engine inside. So you have to rewrite you query.
Option 1: start from label2 and go t label1. This should return the same result
g.V().hasLabel('label2').in().hasLabel('label1')
Option2: try to use unique edge labels and check edge label instead
g.V().hasLabel('label1').where(_.outE('label1_label2'))
I want to create 1000+ Edges in a single query.
Currently, I am using the AWS Neptune database and gremlin.net for creating it.
The issue I am facing is related to the speed. It took huge time because of HTTP requests.
So I am planning to combine all of my queries in a string and executing in a single shot.
_g.AddE("allow").From(_g.V().HasLabel('person').Has('name', 'name1')).To(_g.V().HasLabel('phone').Where(__.Out().Has('sensor', 'nfc'))).Next();
There are chances that the "To" (target) Vertex may not be available in the database. When it is the case this query fails as well. So I had to apply a check if that vertex exists before executing this query using hasNext().
So as of now its working fine, but when I am thinking of combining all 1000+ edge creation at once, is it possible to write a query which doesn't break if "To" (target) Vertex not found?
You should look at using the Element Existence pattern for each vertex as shown in the TinkerPop Recipes.
In your example you would replace this section of your query:
_g.V().HasLabel('person').Has('name', 'name1')
with something like this (I don't have a .NET environment to test the syntax):
__.V().Has('person', 'name', 'name1').Fold().
coalesce(__.Unfold(), __.AddV('person').Property('name', 'name1')
This will act as an Upsert and either return the existing vertex or add a new one with the name property. This same pattern can then be used on your To step to ensure that it exists before the edge is created as well.
I am creating 2 users(uid=1 & uid=2) with 2 versions each.
g.addV('user1').property('uid',1).property('version',1)
.addV('user1').property('uid',1).property('version',2)
.addV('user1').property('uid',2).property('version',1)
.addV('user1').property('uid',2).property('version',2)
I want to get the latest version from each uid, I am using the uid as a groupBy key and getting the latest as shown
g.V().hasLabel('user1')
.group().by('uid').by(fold().order(Scope.local).by('version', Order.desc).unfold().limit(1)) //GraphTraversal<Vertex,Map<Object, Object>>
.flatmap(t -> t.get().values().iterator()) // convert to GraphTraversal<Vertex, Vertex>
//traverse out and get the path
.out('friend').path().by(elementMap())
Is the best approach for this requirement?
What would be the gremlin preferred way to convert the Map to a Vertex inside the flatmap rather than using the lambda? Suppose I want to add further steps after this.
Appreciate any help!
The group step has two modes. Without a label it acts as a barrier but with a label it acts as a side effect. You can have results flow through a group using your data as follows.
gremlin> g.V().group('x').by('uid').by(values('version').max())
==>v[42306]
==>v[42309]
==>v[42312]
==>v[42315]
==>v[42318]
gremlin> g.V().group('x').by('uid').by(values('version').max()).cap('x')
==>[1:2,2:2]
You can add more traversal steps of course before you decide what you want to do with the group. Such as:
g.V().group('x').by('uid').by(values('version').max())out()...
i create the property for a vertex, as
g.addV('sth').property('p1', '1').property('p2', '2').property('p3', '3')
however when I query the vertex, like
g.V().hasLabel('sth').valueMap(true)
or
g.V().hasLabel('sth').properties()
the order of the properties is lost, I get
p3, p1, p2, how can I make sure I can order the property like the order I created.
Gremlin does not guarantee order for any result stream so if you need a specific order then you need to sort yourself:
gremlin> g.V().hasLabel('sth').valueMap().order(local).by(keys,desc)
==>[p3:[3],p2:[2],p1:[1]]
Of course, that isn't insertion order and I'm not sure how you would be able to achieve that as Gremlin does not have that information available to it - only the underlying graph database does. You may be beholden to what the underlying graph allows with respect to this.
I want to return a node where the node has a property as a specific uuid and I just want to return one of them (there could be several matches).
g.V().where('application_uuid', eq(application_uuid).next()
Would the above query return all the nodes? How do I just return 1?
I also want to get the property map of this node. How would I do this?
You would just do:
g.V().has('application_uuid', application_uuid).next()
but even better would be the signature that includes the vertex label (if you can):
g.V().has('vlabel', 'application_uuid', application_uuid).next()
Perhaps going a bit further if you explicitly need just one you could:
g.V().has('vlabel', 'application_uuid', application_uuid).limit(1).next()
so that both the graph provider and/or Gremlin Server know your intent is to only next() back one result. In that way, you may save some extra network traffic/processing.
This is a very basic query. You should read more about gremlin. I can suggest Practical Gremlin book.
As for your query, you can use has to filter by property, and limit to get specific number of results:
g.V().has('application_uuid', application_uuid).limit(1).next()
Running your query without the limit will also return a single result since the query result is an iterator. Using toList() will return all results in an array.