Wednesday, March 18, 2020

XML Batching(Aggregation) in Logic App

Introduction

One of my connection on Linkedin asked for help 



So basically his requirement is to send all the individual records in a group to CRM endpoint i.e. a Batch of individual records. This is called Aggregator or Batching pattern in Integration.

aggregator pattern
When we say we want to group messages then comes a question as to how to  wrap them.In BizTalk we handle such scenario with help of Envelope schema (for Debatching and Batching). 

In logic app there is a special trigger for grouping of the messages - Batch trigger.


In last post Batching(Aggregating) messages in Logic App we saw how to group JSON messages, in this post let's see how to batch XML message.

One of the primary thing to consider is valid that XML document has single Root Node.

We would create two logic app 1. XMLBatchProcessor 2. BatchProcessCaller


Steps to implement Aggregator/Batching Pattern in Logic App


1. Create a XMLBatchProcessor Logic App

From the Azure Portal select Create a resource -> search of “Logic App” -> click Create button

After instance is created, go to logic app designer and to add trigger - search for Batch. Select the Batch message trigger and configure batch process trigger .

  • Batch Mode 
Here we have two option

- Inline: For defining release criteria inside the batch trigger itself (for this post am using this - it's kind of hard coding). 

IMO This should be opted if you don't have integration account or you have limited batch processing requirement.

- Integration Account: Ideally, this is should be preferred, as it helps for defining multiple release criteria configurations and also you don't have to make updates in Logic app every time release criteria is changed . It is like a configuration file sitting in an integration account,so you can maintain these configurations all in one place rather than in separate logic apps
  • Batch Name
The name for your batch, which is "CommonBatch" in this example  and applies only to Inline batch mode
  • Release Criteria

As we have used Inline batch mode, we need to select the criteria to meet before processing each batch (we can select multiple criteria also):
- Message count based: Release the batch based on the number of messages collected by the batch.
- Size based: Release the batch based on the total size in bytes for all messages collected by that batch.
- Schedule: Release the batch based on a recurrence schedule, which specifies an interval and frequency. In the advanced options, you can also select a time zone and provide a start date and time.
- Select all: Use all the specified criteria.

Here Message count is selected with count as 3

configuring batch process trigger in logic app

Now, what you want to do with Batched Message? 

We want to wrap this group of xml messages with a Root element tag, so that we get a valid XML Batched message and then finally can send it to the required destination for further processing.

So how we do it -- one option would be to create Azure Function - you will have to write code  which will accept the Batched items and return new batched message. And call this function from your logic app.

Another would be to use Inline code - but it is still in preview and currently only supports Java Script.

Here we will make use of string Variable, using which we do following

Initialize variable with Start tag <RootNode> 

So after the Batch Trigger step , add new action and select variable
Add variable

Select Initialize variable


Give the Variable a Name , String as Datatype and against Value provide the start tag you want , here <BatchedMessages> is used

Initialize variable

Keep on appending each Batched Item

Now add new action -- Append to string variable
Append to string variable

Select Message Content of BatchedItems which is output of BatchTrigger step as a value to append. Note that For each gets automatically added.

values to append



Close the Rootnode tag </RootNode>

Next again we add Append Variable action after Foreach and add closing tag to it.

And now the final step is to send to destination -- for this post have used Send email action with attachment

send email action


Note : Batch trigger is a special trigger meant for collecting messages and it only starts the instance once it's release condition is met - so you won't see it's instance in run history till it reaches it's release point. 

Also you would not be able to call it outside of your subscription or from different region.


2. Create a caller Logic App

From the Azure Portal select Create a resource -> search of “Logic App” -> click Create button.

In designer select http tigger and in next action search for Batch, you should see all the logic apps which have Batchtrigger, select the one created in above step.
call xml processor



As soon as you select it, Trigger Name and Workflow will be auto populated, against Batch Name give the same name used in step 1 and for Message content provide triggerbody.

configure call xml processor

That's it, ready to use.


Testing


Using Postman, sent 3 request(xml) having order details in it in it to the BatchProcessCaller logic app
xml input


And below is the email received - which is sent by XMLBatchProcessor logic app
received email

Downloaded the attachment and following is what we expected

final output






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