Group database records using ESB mule - groovy

Question

I have mule flow which selects few records from database tables which looks like below.
StudentID Subject Mark
1 Maths 98
2 Literature 62
1 Science 56
1 Anatomy 63
3 Zoology 38
2 Algebra 63
Here i need to group the records based on studentID and need to send for further processing. Hence i have placed splitter component immediate after database node. But in MEL expression how can we group the records ?
Is there any other best way to do this ESB mule ?
Update - I need to split the message based on StudentID (group by). I found groovy can do grouping. But whether we can split the messages using groovy.

Answer 1

I would create a Java object and implement callable. Use this method to alter the payload. Then I would use a second database component and use the payload object (MEL) in the second query.
This object transforms data from a Database component output flow to a hybrid object that's used to display JSON with an embedded array of child data.
https://github.com/dlwhitehurst/modusbox-orders/blob/master/src/main/java/org/dlw/transport/OrdersTransformSingleton.java
Check out the return on the callable method and see how you can "transform" the data yourself.
Here's the snippet in the mule config that instances the needed Java component.
<spring:beans>
<spring:bean id="ordersTransform" name="OrdersTransformSingleton"
class="org.dlw.transport.OrdersTransformSingleton" scope="singleton">
</spring:bean>
<spring:bean id="jdbcDataSource" class="org.enhydra.jdbc.standard.StandardDataSource" destroy-method="shutdown">
<spring:property name="driverName" value="com.mysql.jdbc.Driver"/>
<spring:property name="url" value="${database.url}"/>
</spring:bean>
</spring:beans>
The object is used in the flow like this ...
<flow name="get:/orders:api-config">
<set-payload value="[
{
"orderId": 1233,
"placementDate": "2016-06-02",
"customerName": "Sally Hansen",
"orderItems":[
{
"orderItemId": 1323,
"orderId": 438577,
"itemId": 23058,
"itemName": "Salt",
"itemCount": 3,
"qtyItemCost": "$2.76"
},
{
"orderItemId": 1323,
"orderId": 438577,
"itemId": 23058,
"itemName": "Pepper",
"itemCount": 3,
"qtyItemCost": "$8.79"
}
]
},
{
"orderId": 1233,
"placementDate": "2016-06-02",
"customerName": "Billy Wilson",
"orderItems":[
{
"orderItemId": 1323,
"orderId": 438577,
"itemId": 23058,
"itemName": "Wheat Flour",
"itemCount": 3,
"qtyItemCost": "$10.12"
},
{
"orderItemId": 1323,
"orderId": 438577,
"itemId": 23058,
"itemName": "Tomato Paste",
"itemCount": 3,
"qtyItemCost": "$9.21"
}
]
}
]" doc:name="Set Payload"/>
<db:select config-ref="MySQL_Configuration" doc:name="Database">
<db:parameterized-query><![CDATA[SELECT a.orderId, a.customerName, a.placementDate, b.orderItemId, b.itemId, c.itemName, b.itemCount, c.itemCost FROM modusbox.orders a, modusbox.orderitems b, modusbox.items c WHERE a.orderId = b.orderId AND b.itemId = c.itemId]]></db:parameterized-query>
</db:select>
<component doc:name="Java">
<spring-object bean="OrdersTransformSingleton" />
</component>
<json:object-to-json-transformer doc:name="Object to JSON"/>
<logger level="INFO" doc:name="Logger"/>
</flow>

Answer 2

Better place dataweave component and use 'groupBy' logic.
https://docs.mulesoft.com/mule-user-guide/v/3.7/dataweave-reference-documentation#group-by

Answer 3

DataWeave is the right option for groupBy. If you don't have DataWeave as choice (using Community Edition), you can have a quick win with script engine groovy.
List which should be groupBy attribute mail
[
{
"mail": "smith#example.com",
"name": "lastname",
"value": "Smith"
},
{
"mail": "smith#example.com",
"name": "firstname",
"value": "John"
},
{
"mail": "doe#example.com",
"name": "lastname",
"value": "Doe"
},
{
"mail": "doe#example.com",
"name": "firstname",
"value": "Lisa"
}
]
Mule script component
<scripting:component>
<scripting:script engine="groovy">
<![CDATA[flowVars['recipients'].groupBy{it.mail}]]>
</scripting:script>
</scripting:component>
Result of groupBy mail
{
"smith#example.com": [
{
"mail": "smith#example.com",
"name": "lastname",
"value": "Smith"
},
{
"mail": "smith#example.com",
"name": "firstname",
"value": "John"
}
],
"doe#example.com": [
{
"mail": "doe#example.com",
"name": "lastname",
"value": "Doe"
},
{
"mail": "doe#example.com",
"name": "firstname",
"value": "Lisa"
}
]
}
Works fine with Mule 3.8.1 CE.