Mule scopes foreach_scope
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The Foreach scope allows processing of each element in a collection iteratively without losing any message payload data. It splits collections into individual elements, processes them with message processors inside the scope, and returns the original message rather than aggregating into a new collection. This avoids issues like losing XML metadata or needing to transform collection types when using split-aggregate processing. The Foreach scope can iterate over various collection types and properties. It does not make deep copies during processing and changes to element values will persist in the returned message.
![• Fields :
– Display Name :
• Default value = For Each
– Collection :
• No default value
• an expression can be entered that tells Foreach where to find the data it must split
and process.
• Unless this field specifies otherwise, Foreach assumes that the message payload is
the collection.
• Example : collection="#[payload.topic]“
– Counter Variable Name :
• Default value = counter
• Enter a name in this field to label the variable that Foreach uses to record the
number of the elements it has processed.
• If your collection already uses the label counter for another variable, this field is
kept blank and you need to enter a different label for the Counter Variable Name,
such as index.
Foreach Scope - Configuration](https://image.slidesharecdn.com/mulescopesforeachscope-161012173114/85/Mule-scopes-foreach_scope-9-320.jpg)
Mule scopes foreach_scope
- 2. • The Foreach scope splits a collection into elements and processes them iteratively through the processors embedded in the scope. • Then returns the original message to the flow. • The second point is the core difference between the Foreach scope and other splitter and Aggregator pairs. Foreach Scope
- 3. • Limitations of Splitter – Aggregator : – Under some circumstances, splitting a message collection into pieces can cause certain vital bits of XML — metadata in the header or footer, for example — to be dropped from the re- aggregated XML. – When certain collection types are split- Java, for example - into many pieces for processing, the collection may be re- aggregated into a different collection type - MuleMessageCollection, for example. Which then reqiures some extra flow steps to transform the processed message collection back into its original collection type. – When we split, process, or aggregate a message collection, you must choose among several splitter and aggregator types. Sometimes, it proves difficult to determine which splitter/aggregator combination best suits the message processing needs. Foreach Scope
- 4. • Advantages of Foreach : – Foreach splits collections into elements, then processes them iteratively without losing any of the message payload. – After Foreach splits a message collection and processes the individual elements, it doesn’t re-aggregate those individual elements into a MuleMessageCollection; rather, it returns the original message. ("Java in, Java out" rather than "Java in, MuleMessageCollection out.") – The Foreach scope is versatile; it can iteratively process elements from any type of collection, including maps, lists, arrays, and MuleMessageCollections. – The Foreach scope can split and process collections of elements that are not part of the message payload. For example, Foreach can process message property collections (metadata) from the message header. Foreach Scope
- 5. • Note : – Foreach does not make a deep copy of the data when processing a message nor when returning the original message to the flow. – If the elements are mutable objects (for example, a bean with different fields in it) and any of the message processors embedded in the Foreach scope modifies a value of the original object (for example, one of the fields), then the changes to the fields persist once the foreach returns the original message to the flow. Foreach Scope
- 6. 1.Add a Foreach scope in your flow at the point where you want to initiate the Foreach scope processing. Foreach Scope - Configuration
- 7. 2.Insert one or more message processors inside the Foreach scope area to define how Mule should process each element within the message collection. The Foreach scope can contain any number of message processors as well as references to child flows. Foreach Scope - Configuration
- 8. • Note : – The only type of message processor you cannot drag into a Foreach scope is an inbound connector. – If a two-way connector is dragged into a Foreach scope, Mule automatically converts it to an outbound-only connector. Foreach Scope - Configuration
- 9. • Fields : – Display Name : • Default value = For Each – Collection : • No default value • an expression can be entered that tells Foreach where to find the data it must split and process. • Unless this field specifies otherwise, Foreach assumes that the message payload is the collection. • Example : collection="#[payload.topic]“ – Counter Variable Name : • Default value = counter • Enter a name in this field to label the variable that Foreach uses to record the number of the elements it has processed. • If your collection already uses the label counter for another variable, this field is kept blank and you need to enter a different label for the Counter Variable Name, such as index. Foreach Scope - Configuration
- 10. • Fields : – Root Message Variable Name : • Default value = rootMessage • Enter a name in this field to label the variable that Foreach uses to reference the complete, unsplit message collection. • If your collection already uses the labelrootMessage for another variable, this field is blank and you need to enter a different label for the Root Message Variable Name. Foreach Scope - Configuration
- 11. • Error Handling: – If a message in a collection throws an exception, Foreach stops processing that collection and invokes the exception strategy. – Foreach throws an IllegalArgumentException whenever two conditions hold true: • It receives a message payload that is not a collection • a message collection outside the message payload (defined by entering an expression in the Collection field in the Studio Visual Editor or including the collectionattribute in XML configuration.) is not identified Foreach Scope
- 12. • Considerations when persisting data : – In case the message inside the foreach scope is persisted, not only the item in the collection is serialized but also all the variables associated with the current message. – The rootMessage variable, associated with the message, contains a reference of the complete, unsplit message collection that could potentially be holding thousands of items. – Therefore, serialization/deserialization of the rootMessage variable could impact memory consumption considerably when this collection is large enough. – To avoid this issue you must first remove the rootMessage variable from the message before persisting it. – In Studio, you can drag a Variable message processor inside your scope and set it to "Remove Variable". Foreach Scope