In this blog we will discuss some of the predicate functions and then user defined functions.

Predicate functions

Predicates are boolean functions that return true or false for a given set of input. They are most commonly used to filter out subgraphs in the WHERE part of a query.

Some of the predicate functions are explained below:

Exists():

Exists here returns true if the specified property is existing in the graphs, node and relationships.

Syntax:

exists(property)

It returns an agtype boolean value.

Query:

SELECT *
FROM cypher('graph_name', $$
     MATCH (n)
     WHERE exists(n.surname)
     RETURN n.first_name, n.last_name
$$) as (first_name agtype, last_name agtype);

Exists(path):

Exists(path) returns true if a path already exists there.

Syntax:

Exists(path)

Query:

SELECT *
FROM cypher('graph_name', $$
     MATCH (n)
     WHERE exists(n)-[]-(name: 'Willem Defoe')
     RETURN n.full_name
$$) as (full_name agtype);

User Defined functions:

In apache age users can add their custom functions to age. When we use cypher function calls we use default namespace of age catalog. A function can be used outside the name space and this can be done by adding namespace before the function name.

Syntax:

namespace_name.function_name

Query:

SELECT *
FROM cypher('graph_name', $$
RETURN pg_catalog.square(5)
$$ as (result agtype);

The above query will return square of the number 5.