Graph databases come with enhanced connectivity of data and whiteboard friendly paradigm. Some, like Neo4j, also brings a gremlin in your code : it is one of the most powerful graph query langage. It brings a refreshing look at how we store web of data and search for it. Gremlin provides an abstract layer that make it easy to express your business logic without fighting with the code. It may even change your mind on object oriented programming.

1. A gremlin
ate my graph
Barcelona, Spain, October, 30th 2015

2. Agenda
Discover the Graph
Steps with a gremlin
The state of the Gremlin

3. Damien Seguy
CTO at Exakat
PHP code as Dataset
Speaker

5. What is gremlin?
V :Vertices, or nodes or objects
E : Edges, or links or relations
G : graph, or the dataset

6. The Vertices
g.vrepresents all the vertices
g.v(1) is one of the nodes
Vertices always have an id
g.v(1) => v(1)
1

7. g.v(1).id => 1
g.v(1).name => apply_filter
g.v(1).version => true
g.v(1).compat => [4.0, 4.1, 4.2, 4.3]
// non-existing properties
g.v(1).isFedAfterMidnight => null
Properties
Graph is schemaless
apply_filter

8. Vertice discovery
Use map to discover the graph
g.v(2).map => {name=wp_die, leaf=true}
wp_die

9. The Edges
Edges have id, properties
also : start, end and label
g.E represents all the edges
g.e(1) is the edge with Id 1

10. g.e(1) => e(1)
g.e(1).map => { }
g.e(1).id => 1
g.e(1).label => CALLS
Edge discovery
wp_diewp_ajax_fetch
_list
CALLS
Edges link the vertices

11. g.e(5).outV => v(2)
g.e(6).outV => v(3)
g.e(1).inV => v(4)
Running on the Edges
2
3
4
1
5
6
7
Directed graph

12. g.v(1).out => v(2)
v(3)
g.v(1).in => v(4)
g.v(1).both => v(2)
v(3)
v(4)
Following Edges
2
3
4
1
5
6
7
g.v(1).inE => e(7)

13. g.v(1).out.id => 2
3
g.v(2).in.in.id => 4
g.v(1).both.id => 2
3
4
Chaining
2
3
4
1
5
6
7

14. Wordpress Calls Graph
The graph of all Wordpress internal function calls
function
:name
function
:name
CALLS

15. function functionCALLS

17. g.v(19).out(‘CALLS’).name => wp_hash_password
wp_cache_delete
g.v(19).in(‘CALLS’).name => reset_password
wp_check_password
Calling home
wp_set_
password
reset_
password
wp_hash_
password
wp_check_
password
wp_cache_
delete
CALLS
CALLS
CALLS
CALLS

18. g.v(30).out(‘CALLS’)
.retain([g.v(30)])
.name => get_category_parents
Is it Recursive
get_permalink get_category_
link
get_category_
parents
id : 30
CALLS
CALLS
CALLS

19. Is it Recursive
g.v(30).in(‘CALLS’)
.retain([g.v(30)])
.name => get_category_parents
get_permalink get_category_
link
get_category_
parents
id : 30
CALLS
CALLS
CALLS

20. g.v(47).out(‘CALLS’).except([g.v(47)])
.out('CALLS').retain([g.v(47)])
.name
=> wp_trash_comment
Ping-Pong Function
CALLS
wp_trash
_comment
id: 47
wp_delete
_comment
id : 148
CALLS
CALLS
CALLS
CALLS
CALLS
CALLS
CALLS
CALLS

21. Up to now
nodes and vertices : basic blocs
in and out (and both) : navigation
except(), retain(), in(‘label’) : filtering
Starting at the vertices

22. Traversing the graph
Finding nodes in the graph that satisfy criteria
Traversing involves listing nodes, following
links, applying filters, processing data until all
conditions are met
Starting point : g.V and g.E

23. Counting
g.V.count() => 2691
g.E.count() => 9013
function functionCALLS

24. Sampling
g.V[0..3].name => do_activate_header
do_action
wpmu_activate_stylesheet
comment_footer_die
g.V[0..3].id => 1
3
5
4

25. Filtering
g.V.has('name','wp_die') => v(25);
wp_die

26. Dying Functions
g.V.out('CALLS')
.has('name','wp_die')
.count() => 84
???? wp_dieCALLS

27. g.V.out('CALLS')
.has('name','wp_die')
.name =>
Dying Functions
???? wp_dieCALLS
PROCESSING
wp_die
wp_die
wp_die
wp_die
wp_die
wp_die
wp_die
wp_die
wp_die

28. g.V.has('name','wp_die')
.in('CALLS')
.name => wp_ajax_trash_post
wp_ajax_delete_post
wp_ajax_delete_meta
wp_ajax_delete_link
wp_ajax_delete_tag
wp_ajax_delete_comment
wp_ajax_oembed_cache
wp_ajax_imgedit_preview
we_ajax_fetch_list
Dying Functions
???? wp_dieCALLS
PROCESSING

29. g.V.as('start')
.out('CALLS')
.has('name','wp_die')
.back('start')
.name => wp_ajax_trash_post
wp_ajax_delete_post
wp_ajax_delete_meta
wp_ajax_delete_link
wp_ajax_delete_tag
wp_ajax_delete_comment
wp_ajax_oembed_cache
wp_ajax_imgedit_preview
Dying Functions
???? wp_dieCALLS
PROCESSING

30. Relay Functions
g.V.filter{ it.out('CALLS').count() == 1}
.count() => 650
CALLS
CALLS
CALLS

31. Closures
Steps often offer possibility for closure
Closure is between {} , uses ‘it’ as current node,
is written in Groovy (or else)
Closure often have a standard default behavior,
so they are sometimes stealth

32. Applied to properties
Non standard functions
g.V.filter{ it.name != it.name.toLowerCase()}
.count() => 73

33. Leaf and Roots
LEAF
ROOT
g.V.filter{ it.out('CALLS').any() == false}
.count() => 407
g.V.filter{ it.in('CALLS').any() == false}
.count() => 1304

34. Get Linking Index
g.V.transform{['name':it.name,
'links':it.in('CALLS').count()]}
=> ...
{'name':wpmu_signup_stylesheet, 'links':0}
{'name':show_blog_form, 'links':7}
{'name':validate_blog_form, 'links':3}
{'name':show_user_form, 'links':4}

35. Get Called Index
g.V.transform{['name':it.name,
'links':it.in('CALLS').count()]
}
.order{ it.a.links <=> it.b.links}
=> {'name':get_post, 'links':191}
{'name':get_option, 'links':218}
{'name':_deprecated_function, 'links':296}
{'name':__, 'links':442}
{'name':apply_filters, 'links':598}

36. Most linked Function
groupCount(m)
m = [:];
g.V.groupCount(m);
m;
=> {
v[1] = 1,
v[2] = 1,
...
v[47] = 1,
}

37. Most linked Function
groupCount(m){key}{value}
m = [:];
g.V.groupCount(m){it.name}
{it.in('CALLS').count()};
m;
=> {
wp_restore_image = 1,
press_this_media_buttons = 0,
WP_Filesystem = 3,
...
}

38. Most linked Function
groupCount(m){key}{value}
m = [:];
g.V.groupCount(m){it.name}
{it.in('CALLS').count()};
m.sort{ -it.value }[0..2];
=> {
apply_filters = 598,
__ = 442,
_deprecated_function = 296
}

39. Most linked Function
m = [:];n = [:];
g.V.groupCount(m){it.name}
{it.in('CALLS').count()}
.groupCount(n){it.name}
{it.out('CALLS').count()};
n.sort{ -it.value}[0..2];
=> {
redirect_canonical = 60,
export_wp = 47,
edit_post = 36

40. SideEffect Steps
sideEffect : emit incoming but allows for side
computation
m = [:];n = [:];
g.V.groupCount(m){it.name}
{it.in('CALLS').count()}
.groupCount(n){it.name}
{it.out('CALLS').count()}
.count();
=> 2692

41. Nature of Steps
filter step : emit input if condition is satisfied :
has(), filter(), retain(), except()
map step : transform input into another object :
in(), out(), BOTH()
sideEffect step : emit input but allows for side
computation : transform, groupCount, each,
sideEffect
Branch and flatMap

42. Lonely Functions
g.V.filter{ it.in('CALLS').any() == false}
.filter{ it.out('CALLS').any() == false}
.sideEffect{ it.lonely = true; }
.count()
=> 184
SELECT, UPDATE AND COUNT

43. Updating a node
g.V.sideEffect{
incoming = it.in('CALLS').count();
}
.each{
it.setProperty('incoming', incoming);
it.setProperty('outgoing',
it.out('CALLS').count());
}

44. Updating The Graph
// removing deprecated functions
g.V.filter{ it.out('CALLS')
.has('name', '_deprecated_function'
.any()
}
.each{
it.bothE.each{ g.removeEdge(it); }
g.removeVertex(it);
}

45. State of Gremlin

46. Apache TinkerPop
http://tinkerpop.incubator.apache.org/
Version : 3.0.2

47. TP2 and TP3
groupCount{}{}
map
group().by().by()
ValueMap()

48. Vendors
StarDog
sqlg

49. Gremlin Variants

50. Gremlin For PHP
https://github.com/PommeVerte/gremlin-php
Get up and running with Tinkerpop 3 and PHP :
https://dylanmillikin.wordpress.com/2015/07/20/
get-up-and-running-with-tinkerpop-3-and-php/
Using with Neo4j : REST API
Older API : neo4jPHP, rexpro-php

51. Thanks
dseguy@exakat.io @exakat
http://www.slideshare.net/dseguy/
on the http://2015.phpconference.es//