Registering and Unregistering User Functions

User-defined functions (UDFs) can be registered in the selected database using the @arangodb/aql/functions module as follows:

var aqlfunctions = require("@arangodb/aql/functions");

To register a function, the fully qualified function name plus the function code must be specified. This can easily be done in arangosh. The HTTP Interface also offers User Functions management.

In a cluster setup, make sure to connect to a Coordinator to manage the UDFs.

Documents in the _aqlfunctions collection (or any other system collection) should not be accessed directly, but only via the dedicated interfaces. Otherwise you might see caching issues or accidentally break something. The interfaces ensure the correct format of the documents and invalidate the UDF cache.

Registering an AQL user function

For testing, it may be sufficient to directly type the function code in the shell. To manage more complex code, you may write it in the code editor of your choice and save it as file. For example:

/* path/to/file.js */
'use strict';

function greeting(name) {
    if (name === undefined) {
        name = "World";
    }
    return `Hello ${name}!`;
}

module.exports = greeting;

Then require it in the shell in order to register a user-defined function:

arangosh> var func = require("path/to/file.js");
arangosh> aqlfunctions.register("HUMAN::GREETING", func, true);

Note that a return value of false means that the function HUMAN::GREETING was newly created, and not that it failed to register. true is returned if a function of that name existed before and was just updated.

aqlfunctions.register(name, code, isDeterministic)

Registers an AQL user function, identified by a fully qualified function name. The function code in code must be specified as a JavaScript function or a string representation of a JavaScript function. If the function code in code is passed as a string, it is required that the string evaluates to a JavaScript function definition.

If a function identified by name already exists, the previous function definition is updated. Please also make sure that the function code does not violate the Conventions for AQL functions.

The isDeterministic attribute can be used to specify whether the function results are fully deterministic (i.e. depend solely on the input and are the same for repeated calls with the same input values). It is not used at the moment but may be used for optimizations later.

The registered function is stored in the selected database’s system collection _aqlfunctions.

The function returns true when it updates/replaces an existing AQL function of the same name, and false otherwise. It throws an exception if it detects syntactically invalid function code.

Examples

require("@arangodb/aql/functions").register("MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT",
function (celsius) {
  return celsius * 1.8 + 32;
});

The function code is not executed in strict mode or strong mode by default. In order to make a user function being run in strict mode, use use strict explicitly, e.g.:

require("@arangodb/aql/functions").register("MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT",
function (celsius) {
  "use strict";
  return celsius * 1.8 + 32;
});

You can access the name under which the AQL function is registered by accessing the name property of this inside the JavaScript code:

require("@arangodb/aql/functions").register("MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT",
function (celsius) {
  "use strict";
  if (typeof celsius === "undefined") {
    const error = require("@arangodb").errors.ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH;
    AQL_WARNING(error.code, require("util").format(error.message, this.name, 1, 1));
  }
  return celsius * 1.8 + 32;
});

AQL_WARNING() is automatically available to the code of user-defined functions. The error code and message is retrieved via @arangodb module. The argument number mismatch message has placeholders, which we can substitute using format():

invalid number of arguments for function '%s()', expected number of arguments: minimum: %d, maximum: %d

In the example above, %s is replaced by this.name (the AQL function name), and both %d placeholders by 1 (number of expected arguments). If you call the function without an argument, you see this:

arangosh> db._query("RETURN MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT()")
[object ArangoQueryCursor, count: 1, hasMore: false, warning: 1541 - invalid
number of arguments for function 'MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT()',
expected number of arguments: minimum: 1, maximum: 1]

[
  null
]

Deleting an existing AQL user function

aqlfunctions.unregister(name)

Unregisters an existing AQL user function, identified by the fully qualified function name.

Trying to unregister a function that does not exist results in an exception.

Examples

require("@arangodb/aql/functions").unregister("MYFUNCTIONS::TEMPERATURE::CELSIUSTOFAHRENHEIT");

Unregister Group

Delete a group of AQL user functions:

aqlfunctions.unregisterGroup(prefix)

Unregisters a group of AQL user function, identified by a common function group prefix.

This returns the number of functions unregistered.

Examples

require("@arangodb/aql/functions").unregisterGroup("MYFUNCTIONS::TEMPERATURE");

require("@arangodb/aql/functions").unregisterGroup("MYFUNCTIONS");

Listing all AQL user functions

aqlfunctions.toArray()

Returns all previously registered AQL user functions, with their fully qualified names and function code.

aqlfunctions.toArray(prefix)

Returns all previously registered AQL user functions, restricted to a specified group of functions by specifying a group prefix.

Examples

To list all available user functions:

require("@arangodb/aql/functions").toArray();

To list all available user functions in the MYFUNCTIONS namespace:

require("@arangodb/aql/functions").toArray("MYFUNCTIONS");

To list all available user functions in the MYFUNCTIONS::TEMPERATURE namespace:

require("@arangodb/aql/functions").toArray("MYFUNCTIONS::TEMPERATURE");