Custom, Cypher Based Procedures and Functions

I wanted for a long time to be able to register Cypher statements as proper procedures and functions, so that they become callable in a standalone way.

You can achieve that with the apoc.custom.asProcedure and apoc.custom.asFunction procedure calls. Those register a given Cypher statement, prefixed with the custom.* namespace, overriding potentially existing ones, so you can redefine them as needed.

Here is a simple example:

CALL apoc.custom.asProcedure('answer','RETURN 42 as answer')

This registers the statement as procedure custom.answer that you then can call. As no information on parameter and return types is given, it just returns a stream of columns of maps called row.

CALL custom.answer YIELD row
RETURN row.answer

The same is possible as a function:

CALL apoc.custom.asFunction('answer','RETURN 42')
If you override procedures or functions you might need to call call dbms.clearQueryCaches() as lookups to internal id’s are kept in compiled query plans.

Custom Procedures with apoc.custom.asProcedure

Given statement will be registered as a procedure, the results will be turned into a stream of records.

Table 1. Parameters
name default description

name

none

dot-separated name, will be prefixed with custom

statement

none

cypher statement to run, can use $parameters

mode

read

execution mode of the procedure: read, write, or schema

outputs

[["row","MAP"]]

List of pairs of name-type to be used as output columns, need to be in-order with the cypher statement, the default is a special case, that will collect all columns of the statement result into a map

inputs

[["params","MAP","{}"]]

Pairs or triples of name-type-default, to be used as input parameters. The default just takes an optional map, otherwise they will become proper paramters in order

description

""

A general description about the business rules implemented into the procedure

The type names are what you would expect and see in outputs of dbms.procedures or apoc.help just without the ?. The default values are parsed as JSON.

Type Names

  • FLOAT, DOUBLE, INT, INTEGER, NUMBER, LONG

  • TEXT, STRING

  • BOOL, BOOLEAN

  • POINT, GEO, GEOCORDINATE

  • DATE, DATETIME, LOCALDATETIME, TIME, LOCALTIME, DURATION

  • NODE, REL, RELATIONSHIP, PATH

  • MAP

  • LIST TYPE, LIST OF TYPE

  • ANY

Find neighbours of a node by name
CALL apoc.custom.asProcedure('neighbours',
  'MATCH (n:Person {name:$name})-->(nb) RETURN nb as neighbour','read',
  [['neighbour','NODE']],[['name','STRING'], 'get neighbours of a person']);

CALL custom.neighbours('Keanu Reeves') YIELD neighbour;

Custom Functions with apoc.custom.asFunction

Given statement will be registered as a statement, the results into a single value. If the given output type is a list, results will be collected into a list, otherwise the first row will be used. The statement needs to return a single column, otherwise an error is thrown.

Table 2. Parameters
name default description

name

none

dot-separated name, will be prefixed with custom

statement

none

cypher statement to run, can use $parameters

outputs

"LIST OF MAP"

Output type for single output, if the type is a list, then all rows will be collected, otherwise just the first row. Only single column results are allowed. If your single row result is a list you can force a single row by setting the last parameter to true

inputs

[["params","MAP","{}"]]

Pairs or triples of name-type-default, to be used as input parameters. The default just takes an optional map, otherwise they will become proper paramters in order

singleRow

false

If set to true, the statement is treated as single row even with the list result type, then your statement has to return a list.

description

""

A general description about the business rules implemented into the function

The type names are what you would expect and see in outputs of dbms.procedures or apoc.help just without the ?. The default values are parsed as JSON.

List of registered procedures/function with apoc.custom.list

The procedure apoc.custom.list provide a list of all registered procedures/function via apoc.custom.asProcedure and apoc.custom.asFunction

Given the this call:

CALL apoc.custom.list

The the output will look like the following table:

type name description mode statement inputs outputs forceSingle

"function"

"answer"

<null>

<null>

"RETURN $input as answer"

[["input","number"]]

"long"

false

"procedure"

"answer"

"Procedure that answer to the Ultimate Question of Life, the Universe, and Everything"

"read"

"RETURN $input as answer"

[["input","int","42"]]

[["answer","number"]]

<null>

Remove a procedure apoc.custom.removeProcedure

The procedure apoc.custom.removeProcedure allows to delete the targeted custom procedure.

Given the this call:

CALL apoc.custom.removeProcedure(<name>)

Fields:

argument description

name

the procedure name

Remove a procedure apoc.custom.removeFunction

The procedure apoc.custom.removeFunction allows to delete the targeted custom function.

Given the this call:

CALL apoc.custom.removeFunction(<name>)

Fields:

argument description

name

the function name

How to manage procedure/function replication in a Causal Cluster

In order to replicate the procedure/function in a cluster environment you can tune the following parameters:

name type description

apoc.custom.procedures.refresh

long (default 60000)

the refresh time that allows replicating the procedure/function changes to each cluster member