WSO2 ESB Foreach mediator example

Say you have a payload. For example,

	{
	"data":[
	{
	"id":1,
	"name":"abc",
	},
	{
	"id":2,
	"name":"efg",
	},
	{
	"id":3,
	"name":"hij",
	}
	]
	}

view raw payload.json hosted with ❤ by GitHub

Here, you have an array with the root elemet "data". And you need to perform some processing for each of these objects in the array and send the resulting payload to an endpoint. I'm going to use foreach mediator to achieve this.
Lets say following is the resulting payload you want.

	{
	"info":[
	{
	"id":"IDABC1",
	"classid":1,
	"name":"ABC",
	"university":"University of Moratuwa",
	"department":"CSE"
	},
	{
	"id":"IDEFG2",
	"classid":2,
	"name":"EFG",
	"university":"University of Moratuwa",
	"department":"CSE"
	},
	{
	"id":"IDHIJ3",
	"classid":3,
	"name":"HIJ",
	"university":"University of Moratuwa",
	"department":"CSE"
	}
	]
	}

view raw result.json hosted with ❤ by GitHub

This payload contains, a root element "info" under which there is an array of objects having,
1. id element which is created using value of "name" element from original payload, converted to uppercase , value of "id" element from original payload, and the string "ID"
2. classid element which is the value of "id" element from the original payload
3. The "name" from original payload in uppercase.
4. university element which is hard-coded
5. department element which is also hard-coded

And you need to send this resulting payload to some endpoint in JSON format.

Inside foreach mediator I use script mediator to convert the name to uppercase. Then using payload factory mediator I create the payload. And outside the foreach mediator I use send mediator to send the resulting payload to the endpoint.

Here is the sequence.

	<sequence name="my-in-seq">
	<!-- for each object under data element -->
	<foreach expression="//data">
	<sequence>
	<!-- set the "name" attribute of the object as property "temp" -->
	<property expression="//data/name" name="temp"/>
	<!-- Convert "name" value which can be retrieved from "temp" property to uppercase
	and save it in "upperCaseName" property -->
	<script language="js"><![CDATA[var name = mc.getProperty("temp");
	mc.setProperty("upperCaseName",name.toUpperCase());]]></script>
	<!-- create the corresponding resulting object -->
	<payloadFactory media-type="xml">
	<format>
	<!-- let the root of the resulting payload be "info" -->
	<info>
	<!-- set 1st arg value as "id" element -->
	<id>$1</id>
	<!-- set 2nd arg value as "classid" element -->
	<classid>$2</classid>
	<!-- set 3rd arg value as "name" element -->
	<name>$3</name>
	<!-- For the following two elements we are hardcoding values -->
	<university>University of Moratuwa</university>
	<department>CSE</department>
	</info>
	</format>
	<args>
	<!-- The value evaluated from this will be set in place of $1 inside format
	fn:concat('ID',get-property('uppercaseName'),//data/id) will concatenate the string "ID",
	the value of the property "upperCaseName" and the "id" attribute of the object -->
	<arg evaluator="xml" expression="fn:concat('ID',get-property('upperCaseName'),//data/id)"/>
	<!-- The value evaluated from this will be set in place of $2 inside format
	Like this we can use json evaluator too. The xml evaluator equivalent for this
	would be <arg evaluator="xml" expression="//data/id"/>-->
	<arg evaluator="json" expression="$.data.id"/>
	<!-- The value evaluated from this will be set in place of $3 inside format -->
	<arg evaluator="xml" expression="get-property('upperCaseName')"/>
	</args>
	</payloadFactory>
	</sequence>
	</foreach>
	<!-- we want the resulting payload to be in JSON format -->
	<property name="messageType" scope="axis2" value="application/json"/>
	<send>
	<!-- send the resulting payload to this endpoint -->
	<endpoint>
	<http method="POST" trace="disable" uri-template="http://localhost:8080/test"/>
	</endpoint>
	</send>
	</sequence>

view raw foreachmediator.xml hosted with ❤ by GitHub

Let's use the following API to call my-in-seq.

	<api context="/mediatortest" name="mediatortest">
	<resource inSequence="my-in-seq" methods="POST" protocol="http" url-mapping="/mytest"/>
	</api>

view raw api.xml hosted with ❤ by GitHub

Add both above API and sequence to synapse config. We can send a curl request as follows and see how it works.

curl -v -X POST http://localhost:8280/mediatortest/mytest -H"Content-Type:Application/json" -d'{"data":[{"id":1,"name":"abc"},{"id":2,"name":"efg"},{"id":3, "name":"hij"}]}'

view raw foreach-curl-req.sh hosted with ❤ by GitHub

References
[1] https://docs.wso2.com/display/ESB490/ForEach+Mediator