NAME

Neo4j::Cypher::Pattern - Generate Cypher pattern strings

SYNOPSIS

# express a cypher pattern
use Neo4j::Cypher::Pattern qw/ptn/;

ptn->node();
ptn->N(); #alias
ptn->N("varname");
ptn->N("varname",["label"],{prop => "value"});
ptn->N("varname:label");
ptn->N(["label"],{prop => "value"});

ptn->node('a')->related_to()->node('b'); # (a)--(b)
ptn->N('a')->R()->N('b'); # alias
# additional forms
ptn->N('a')->R("varname","typename",[$minhops,$maxhops],{prop => "value"})
   ->N('b'); # (a)-[varname:typename*minhops..maxhops { prop:"value }]-(b)
ptn->N('a')->R("varname:typename")->N('b'); # (a)-[varname:typename]-(b)
ptn->N('a')->R(":typename")->N('b'); # (a)-[:typename]-(b)
ptn->N('a')->R("", "typename")->N('b'); # (a)-[:typename]-(b)
# directed relns
ptn->N('a')->R("<:typename")->N('b'); # (a)<-[:typename]-(b)
ptn->N('a')->R("varname:typename>")->N('b'); # (a)-[varname:typename]->(b)

# these return strings
$pattern->path('varname'); # path variable assigned to a pattern
$pattern->as('varname'); # alias
ptn->compound($pattern1, $pattern2); # comma separated patterns
ptn->C($pattern1, $pattern2); # alias

DESCRIPTION

The Cypher query language of the graph database Neo4j uses patterns to represent graph nodes and their relationships, for selecting and matching in queries. Neo4j::Cypher::Pattern can be used to create Cypher pattern productions in Perl in an intuitive way. It is part of the Neo4j::Cypher::Abstract distribution.

Basic idea : produce patterns by chaining method calls

Neo4j::Cypher::Pattern objects possess methods to represent nodes and relationships. Each method adds its portion of the pattern, with arguments, to the object's internal queue. Every method returns the object itself. When an object is rendered as a string, it concatenates nodes and relationship productions to yield the entire query statement as a string.

These features add up to the following idiom. Suppose we want to render the Cypher pattern

(b {name:"Slate"})<-[:WORKS_FOR]-(a {name:"Fred"})-[:KNOWS]->(c {name:"Barney"})

In Neo4j::Cypher::Pattern, we do

$p = Neo4j::Cypher::Pattern->new()->N('b',{name=>'Slate'})
     ->R('<:WORKS_FOR')->N('a',{name => 'Fred'})
     ->R(':KNOWS>')->N('c',{name=>'Barney'});
print "$p\n"; # "" is overloaded by $p->as_string()

Because you may create many patterns in a program, a short alias for the constructor can be imported, and extra variable assignments can be avoided.

print ptn->N('b',{name=>'Slate'})
     ->R('<:WORKS_FOR')->N('a',{name => 'Fred'})
     ->R(':KNOWS>')->N('c',{name=>'Barney'}), "\n";

Quoting

In pattern productions, values for properties will be quoted by default with single quotes (single quotes that are present will be escaped) unless the values are numeric.

To prevent quoting Cypher statement list variable names (for example), make the name an argument to the pattern constructor:

ptn('event')->N('y')->R("<:IN")->N('e:Event'=> { id => 'event.id' });

# renders (y)<-[:IN]-(e:Event {id:event.id})
# rather than (y)<-[:IN]-(e:Event {id:"event.id"})

METHODS

Constructor new()

pattern(), ptn()

Exportable aliases for the constructor. Arguments are variable names that should not be quoted in rendering values of properties.

node(), N()

Render a node. Arguments in any order:

scalar string: variable name or variable:label
array ref: array of node labels
hash ref: hash of property => value

related_to(), R()

Render a relationship. Arguments in any order:

scalar string: variable name or variable:type
array ref: variable-length pattern:
  [$minhops, $maxhops] 
  [] (empty array)- any number of hops
  [$hops] - exactly $hops
hash ref : hash of property => value

path(), as()

Render the pattern set equal to a path variable:

$p = ptn->N('a')->_N('b');
print $p->as('pth'); # gives 'pth = (a)--(b)'

compound(), C()

Render multiple patterns separated by commas

ptn->compound( ptn->N('a')->to_N('b'), ptn->N('a')->from_N('c'));
# (a)-->(b), (a)<--(c)

Shortcuts _N, to_N, from_N

ptn->N('a')->_N('b'); # (a)--(b)
ptn->N('a')->to_N('b'); # (a)-->(b)
pth->N('a')->from_N('b'); # (a)<--(b)

SEE ALSO

Neo4j::Cypher::Abstract

AUTHOR

Mark A. Jensen
CPAN: MAJENSEN
majensen -at- cpan -dot- org

LICENSE

This software is provided for use under the terms of Perl itself.

COPYRIGHT

(c) 2017 Mark A. Jensen