mule : Merge List of maps into single Map - mule

Question

I have scattergather in my flow, the output of which is a List of Maps, How can I convert that into a single Map in mule?
I have tried combine-collections-transfomer, flatten payload. Nothing seems to be working.

Answer 1

You can you following dataweave code, but it will override duplicate keys
%dw 1.0
%output application/java
---
{(payload)}
Hope this helps.

Answer 2

I would recommend using a custom Java Transformer so you can easily handle special situations such as duplicate keys with different values. A DataWeave function may also be able to do the trick, but you'll need Mule EE.
With a Transformer it's a simple question of Java code:
public class MyMapFlattener extends AbstractMessageTransformer{
public Object transformMessage(MuleMessage message, String outputEncoding) throws TransformerException {
//assuming your payload is the list of map
List<Map<?, ?>> listOfMap = message.getPayload();
Map<Object, Object> finalMap = new HashMap<Object, Object>();
for(Map<?, ?> map : listOfMap){
//you can use putAll if you don't care about duplicates
//finalMap.putAll(map);
// or a more complex algorithm to handle duplicates
for(Entry<?, ?> e : map.entrySet()){
if(finalMap.containsKey(e.getKey())){
//do something to handle situation when key is duplicate...
//you may want to check if both values are equals and skip this
//maybe throw an exception if values are different
//or keep a value
throw new Exception("Duplicate: " + e);
} else {
//key does not exists, put it
finalMap.put(e.getKey(), e.getValue());
}
}
}
return finalMap;
}
}
And then use this transformer in your flow. See the docs for details.

Answer 3

You have multiple ways of doing this one of which is flatten operator which merges 2 arrays into a single array. The other is to do it through the Dataweave Transform map operator and merging them as per your requirements.