Pagination with range and count

[BDP]

I'm building a system that needs paging; the ability to fetch records X through Y. As part of this I need to return the count of the total recordset I'm operating on. What I'm after is a result set like this:

{ userCount: 4,

  users: [

{name:marko, age:29},

{name:vadas, age:27}

]}

I'm trying to use a union to first fetch the count and then the users with a range:

g.V().hasLabel("person").union(__.select("userCount").by(__.count()),__.range(0,1).valueMap())

However that yields:

[

{name:marko, age:29},

{name:vadas, age:27},

{name:josh, age:32},

{name:peter, age:35}

]

... all the persons with no count. I'm not sure why it doesn't respect the range or output the count. How do I construct such a traversal?

[Daniel Kuppitz]

In 3.2.0:

g.V().hasLabel("person").fold().project("users","userCount").by(range(local, 0, 2)).by(count(local))

Prior 3.2.0:

g.V().hasLabel("person").fold().as("users","userCount").select("users","userCount").by(range(local, 0, 2)).by(count(local))

Cheers,

Daniel

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[BDP]

Thank you Daniel! This is perfect.

[BDP]

Let's say I now need to fetch software that each person created as part of the result. It seems like the fold() step precludes me from traversing edges. I'm trying something like this:

g.V().hasLabel("person").fold().as("users","userCount").select("users","userCount").by(range(local, 0, 2).as("persons","created").select("persons","created").by().by(out("created"))).by(count(local))

java.util.ArrayList cannot be cast to org.apache.tinkerpop.gremlin.structure.Vertex

... which I understand is because fold() yielded an ArrayList. Do I need to unfold() at some point? I've tried but can't figure out how to convert back to vertices that I can traverse from.

[BDP]

I should mention that I'm using 3.0.1-incubating. Thanks for any help you can offer.

[Daniel Kuppitz]

Yea, you'e almost had it. This should be the first by() traversal:

range(local, 0, 2).unfold().as("persons","created").select("persons","created").by().by(out("created").fold()).fold()

Cheers,

Daniel

To view this discussion on the web visit https://groups.google.com/d/msgid/gremlin-users/45e40db7-fa58-41e6-b179-592cf351ef40%40googlegroups.com.

[BDP]

Thank you, that's the solution. Here is the working version for anyone following along. I updated it a little to dump the users with valueMap() and emit the language name.

g.V().hasLabel("person").fold().as("users","userCount").select("users","userCount").by(range(local, 0, 2).unfold().as("persons","created").select("persons","created").by(valueMap()).by(out("created").values("lang").fold()).fold()).by(count(local))

==>[users:[[persons:[name:[marko], age:[29]], created:[java]], [persons:[name:[vadas], age:[27]], created:[]]], userCount:4]