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Custom Script Functions

Scripts enable you to write functions in JavaScript and execute them within queries for a stream. A query can access these custom functions the same way as pre-built functions. Use function definitions to define these scripts.

Function parameters are passed into the function logic as an Object[] with the name data.


Scripts enable you to define a function that is not built into stream workers. You do not need to write an extension to define the function logic.


The syntax for a script definition is:

define function <function name>[<javascript>] return <return type> {
<operation of the function>

The defined function can be used in the queries similar to built-in functions:

<function name>( (<function parameter>(, <function parameter>)*)? )

The custom functions have higher precedence than built-in functions.


The following parameters are configured when defining a script.

function nameThe name of the function. By convention, camelCase is used for the function name.
language nameThe name of the programming language used to define the script. Macrometa supports javascript.
return typeThe attribute type of the function’s return. This can be int, long, float, double, string, bool, or object. Here the function implementer should be responsible for returning the output attribute on the defined return type for proper functionality.
operation of the functionThe running logic of the function. This logic should be written in the language specified under the language name, and it should return the output in the data type specified in the return type parameter.

Example 1

This stream worker uses a function to perform concatenation using JavaScript and return the output as a string.

@App:description("Calculate an average temperature of the room.")

-- Define the source stream.
CREATE STREAM TempStream (deviceID long, roomNo int, temp double);

-- Define the sink stream to receive results of the function.
CREATE SINK DeviceTempStream WITH (type= 'stream', stream='DeviceTempStream', map.type='json') (id string, temp double);

-- Define the function that concatenates the room number and device ID.
CREATE FUNCTION concatFn[javascript] return string {
var str1 = data[0];
var str2 = data[1];
var str3 = data[2];
var response = str1 + str2 + str3;
return response;

-- Query to apply the custom function to the relevant attributes of the input stream definition.
INSERT INTO DeviceTempStream
SELECT concatFn(roomNo,'-',deviceID) AS id, temp
FROM TempStream;

Example 2

Parsing complex JSON data is a good use case for writing custom functions. Consider an example where nested JSON data is received over an input stream. Defining a message schema while defining a stream can be cumbersome or error-prone, so creating a custom function would allow fine-grained control over how the message is parsed.

This example demonstrates how complex data can be parsed using a custom JavaScript function.


CompanyXInputStream receives employee data in JSON format as shown below.

"seqNo": "1200001",
"name": "Raleigh McGilvra",
"address": {
"permanent": {
"street": "236 Pratt Avenue",
"city": "Orchards",
"state": "Washington",
"country": "USA",
"zip": "98662"
"work": {
"street": "1746 Rosebud Avenue",
"city": "Little Rock",
"state": "Arkansas",
"country": "USA",
"zip": "72212"

Custom Function

Write a JavaScript function to convert into a well-formatted string.

define function getWorkAddress[javascript] return string {
work_address = JSON.parse(data[0]).work

// Concatenate all the address fields as a single string
formatted_address = work_address.street + ", " + + ", " + work_address.state + ", " + + ", " +;
return formatted_address

Stream Worker

This stream worker defines the function, then a query uses it to process information from the source and send it to the sink.


-- The source is a Macrometa collection with stream enabled, receiving JSON messages.
CREATE SOURCE CompanyXInputStream WITH (type = 'database', collection = "CompanyXInputStream", collection.type="doc" , replication.type="global", map.type='json') (seqNo string, name string, address string);

--The sink is a stream, mapping messages to JSON.
CREATE SINK CompanyXProfessionalInfo WITH (type = 'stream', stream = "CompanyXProfessionalInfo", replication.type="local", map.type='json') (name string, workAddress string);

-- Define a JavaScript function to process `address` field
CREATE FUNCTION getWorkAddress[javascript] return string {
var work_address = JSON.parse(data[0]).work
var formatted_address = work_address.street + ", " + + ", " + work_address.state + ", " + + ", " +;
return formatted_address

-- Data processing query to the stream to transform data using the `getWorkAddress` function.
INSERT INTO CompanyXProfessionalInfo
SELECT name, getWorkAddress(address) AS workAddress
FROM CompanyXInputStream;