Mule 4 - How to do error handling inside a cache scope? - mule

Question

I'm using cache scope and object store to cache data returned from a Salesforce Query using Salesforce Connector.
I've added On error continue to catch any Salesforce Connector exceptions.
If there is an exception in Salesforce Connector (like Salesforce Connectivity), the application throws an exception and executes On error continue block, but when it is called again application hangs at the cache scope and doesn't give any response/error message. Also, On error continue block is executed thrice when the application is executed first time.
It's running fine in debug mode.
Code:
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:os="http://www.mulesoft.org/schema/mule/os" xmlns:ee="http://www.mulesoft.org/schema/mule/ee/core"
xmlns:salesforce="http://www.mulesoft.org/schema/mule/salesforce"
xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:doc="http://www.mulesoft.org/schema/mule/documentation" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/salesforce http://www.mulesoft.org/schema/mule/salesforce/current/mule-salesforce.xsd
http://www.mulesoft.org/schema/mule/ee/core http://www.mulesoft.org/schema/mule/ee/core/current/mule-ee.xsd
http://www.mulesoft.org/schema/mule/os http://www.mulesoft.org/schema/mule/os/current/mule-os.xsd">
<http:listener-config name="HTTP_Listener_config" doc:name="HTTP Listener config" doc:id="6a5b02b3-836d-43b5-9dbe-41719d20258f" >
<http:listener-connection host="0.0.0.0" port="8081" />
</http:listener-config>
<salesforce:sfdc-config name="Salesforce_Config" doc:name="Salesforce Config" doc:id="3facafa3-5d07-4717-901a-487f0cdeabb2" >
<salesforce:basic-connection username="..." password="..." securityToken="..." url="https://login.salesforce.com/services/Soap/u/48.0" />
</salesforce:sfdc-config>
<ee:object-store-caching-strategy name="Caching_Strategy" doc:name="Caching Strategy" doc:id="4ebcc02a-3c51-445b-bee5-0c95e4ce6e01" keyGenerationExpression="#['1']" >
<os:private-object-store persistent="false" maxEntries="1" entryTtl="1" />
</ee:object-store-caching-strategy>
<flow name="test-errorFlow" doc:id="49520788-7379-45cb-9276-cdb6b268398c" >
<http:listener doc:name="Listener" doc:id="ce5faf93-3153-4f93-8313-90d465f920c6" config-ref="HTTP_Listener_config" path="/test" allowedMethods="GET">
<http:response statusCode="#[vars.httpStatus]" />
<http:error-response statusCode="#[vars.httpStatus]" >
<http:body ><![CDATA[#[error]]]></http:body>
</http:error-response>
</http:listener>
<ee:cache doc:name="Cache" doc:id="ae4e7d76-0f98-4202-9a51-59373ea3ee1c" cachingStrategy-ref="Caching_Strategy">
<salesforce:query doc:name="Query" doc:id="1498398a-7b1f-4a27-aff8-3991d4e9cbca" config-ref="Salesforce_Config">
<salesforce:salesforce-query><![CDATA[Select Id, Name from Account]]></salesforce:salesforce-query>
</salesforce:query>
</ee:cache>
<ee:transform doc:name="Transform Message" doc:id="f864be76-86a9-4726-b1f1-586ffeabb0db" >
<ee:message >
<ee:set-payload ><![CDATA[%dw 2.0
output application/json
---
payload]]></ee:set-payload>
</ee:message>
</ee:transform>
<error-handler >
<on-error-continue enableNotifications="true" logException="true" doc:name="On Error Continue" doc:id="038cd795-2174-4d9a-b759-2921dd12a64e" type="ANY">
<logger level="INFO" doc:name="Logger" doc:id="186587c2-0beb-416a-b589-7239a2cba7dd" message="#[error]"/>
</on-error-continue>
</error-handler>
</flow>
</mule>

Answer 1

'On error continue' means to finish flow even if error occurs. But finishing flow does not mean that it did its job - in particular cache value was not obtained. That's the reason the erst is failing.
Rearrange your flow - if cache value is null - run cache again and again ( for example https://docs.mulesoft.com/mule-runtime/4.3/until-successful-scope ) and only success continue your regular flow with existing real cache value.

Answer 2

The problem is likely that there is nothing to cache, because the error aborted the execution.
You can either use a Try scope to handle the error inside the Cache scope, or call to another flow with a flow-ref, and handle the error inside that other flow.
Example:
<ee:cache doc:name="Cache" cachingStrategy-ref="Caching_Strategy">
<try>
<salesforce:query doc:name="Query" config-ref="Salesforce_Config">
<salesforce:salesforce-query><![CDATA[Select Id, Name from Account]]></salesforce:salesforce-query>
</salesforce:query>
<error-handler>
<on-error-continue>
....
</on-error-continue>
</error-handler>
</try>
</ee:cache>