NAME

REST::Neo4p::Query - Execute Neo4j Cypher queries

SYNOPSIS

REST::Neo4p->connect('http:/127.0.0.1:7474');
$query = REST::Neo4p::Query->new('MATCH (n) WHERE n.name = "Boris" RETURN n');
$query->execute;
$node = $query->fetch->[0];
$node->relate_to($other_node, 'link');

DESCRIPTION

REST::Neo4p::Query encapsulates Neo4j Cypher language queries, executing them via REST::Neo4p::Agent and returning an iterator over the rows, in the spirit of DBI.

Streaming

execute() captures the Neo4j query response in a temp file. fetch() iterates (in a non-blocking way if possible) over the JSON in the response using the incremental parser of JSON::XS (see REST::Neo4p::ParseStream if interested). So go ahead and make those 100 meg queries. The tempfile is unlinked after the iterator runs out of rows, or upon object destruction, whichever comes first.

Parameters

REST::Neo4p::Query understands Cypher query parameters. These are represented in Cypher, unfortunately, as dollar-prefixed tokens.

MATCH (n) WHERE n.first_name = $name RETURN n

Here, $name is the named parameter.

Don't forget to escape the dollar sign if you're also doing string interpolation:

$prop = "n.name";
$qry = "MATCH (n) WHERE $prop = \$name RETURN n";

A single query object can be executed multiple times with different parameter values:

my $q = REST::Neo4p::Query->new(
          'MATCH (n) WHERE n.first_name = $name RETURN n'
        );
foreach (@names) {
  $q->execute(name => $_);
  while ($row = $q->fetch) {
   ...process
  }
}

This is very highly recommended over creating multiple query objects like so:

foreach (@names) {
  my $q = REST::Neo4p::Query->new(
            "MATCH (n) WHERE n.first_name = '$_' RETURN n"
          );
  $q->execute;
  ...
}

As with any database engine, a large amount of overhead is saved by planning a parameterized query once. In addition, the REST side of the Neo4j server will balk at handling 1000s of individual queries in a row. Parameterizing queries gets around this issue.

Paths

If your query returns a path, fetch() returns a REST::Neo4p::Path object from which you can obtain the Nodes and Relationships.

Transactions

See "Transaction Support (Neo4j Version 2.0+)" in REST::Neo4p.

METHODS

new()

$stmt = 'MATCH (n) WHERE id(n) = $node_id RETURN n';
$query = REST::Neo4p::Query->new($stmt,{node_id => 1});

Create a new query object. First argument is the Cypher query (required). Second argument is a hashref of parameters (optional).

execute()

$numrows = $query->execute;
$numrows = $query->execute( param1 => 'value1', param2 => 'value2');
$numrows = $query->execute( $param_hashref );

Execute the query on the server. Not supported in batch mode.

fetch()

fetchrow_arrayref()

$query = REST::Neo4p::Query->new('MATCH (n) RETURN n, n.name LIMIT 10');
$query->execute;
while ($row = $query->fetch) { 
  print 'It works!' if ($row->[0]->get_property('name') == $row->[1]);
}

Fetch the next row of returned data (as an arrayref). Nodes are returned as REST::Neo4p::Node objects, relationships are returned as REST::Neo4p::Relationship objects, scalars are returned as-is.

err(), errstr(), errobj()

$query->execute;
if ($query->err) {
  printf "status code: %d\n", $query->err;
  printf "error message: %s\n", $query->errstr;
  printf "Exception class was %s\n", ref $query->errobj;
}

Returns the HTTP error code, Neo4j server error message, and exception object if an error was encountered on execution.

err_list()

finish()

while (my $row = $q->fetch) {
  if ($row->[0] eq 'What I needed') {
    $q->finish();
    last;
  }
}

Call finish() to unlink the tempfile before all items have been fetched.

ATTRIBUTES

RaiseError

$q->{RaiseError} = 1;

Set $query->{RaiseError} to die immediately (e.g., to catch the exception in an eval block).

ResponseAsObjects

$q->{ResponseAsObjects} = 0;
$row_as_plain_perl = $q->fetch;

If set to true (the default), query reponses are returned as REST::Neo4p objects. If false, nodes, relationships and paths are returned as simple perl structures. See "as_simple()" in REST::Neo4p::Node, "as_simple()" in REST::Neo4p::Relationship, "as_simple()" in REST::Neo4p::Path for details.

Statement

$stmt = $q->{Statement};

Get the Cypher statement associated with the query object.

SEE ALSO

DBD::Neo4p, REST::Neo4p, REST::Neo4p::Path, REST::Neo4p::Agent.

AUTHOR

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

LICENSE

Copyright (c) 2012-2021 Mark A. Jensen. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

cpanm REST::Neo4p

perl -MCPAN -e shell
install REST::Neo4p