XPATH: Providing a default response if an array search does not find the required item?

Question

This is a problem that I am facing in Oracle Integration Cloud when using the assignment expression editor. In my problem, I get records from a DB table that have name/value columns. I have variables for the possible names and want to assign the values in an assign action: varParticipantId, varOrgId, varPersonId (there are more). So, if the NAME column is ParticpantId and the VALUE column is 12345 then I want to set the variable varParticipantId = 12345.

If I have a result from the table like this (SELECT FROM TABLE WHERE ID = "AAAA"), then my xpath works and varParticipantId is set to the result of the XPATH query, 12345.

ID	NAME	VALUE
AAAA	ParticipantId	12345
AAAA	OrgId	54321

The XML would look like this (simplified):

<response>
    <records>
        <id>AAAA</id>
        <name>ParticipantId</name>
        <value>12345</value>
    </records>
    <records>
        <id>AAAA</id>
        <name>OrgId</name>
        <value>54321</value>
    </records>
</response>

This is the assignment expression (simplified): $getRefs/getResponse/....../records[name=‘ParticpantId’]/value

However if the result set doesn’t have the record I’m looking for then it fails, e.g. (SELECT FROM TABLE WHERE ID = "BBBB")

ID	NAME	VALUE
BBBB	OrgId	98765

<response>
    <records>
        <id>BBBB</id>
        <name>OrgId</name>
        <value>98765</value>
    </records>
</response>

What I want to do in this case is to set the variable varParticipantId = “”, i.e. have a default return of null if records[name=‘xxxxxx’] is not found. Is this doable with XPATH?

This is the XPATH query

$getRefs/getResponse/....../records[name=‘ParticpantId’]/value

If no record with name = ParticpantId, I get this error

summary=<summary>The &lt;from> value is invalid.Xpath expression associated with &lt;from> in copy assign activity is invalid.There is an user error that results in missing element value(s) in the xpath query.</summary>,activity=<activity>29726865-BpAss30-BpSeq7.3-54</activity>,query=<query>$messagecontext_37.parameters/../nsmpr8:getResponse/nsmpr8:components.schemas.get-response-wrapper/nsmpr0:records[(nsmpr3:referenceAttributeName = “ParticpantId”)]/nsmpr3:referenceAttributeValue_0x737063_</query>

Answer 1

Someone posted this answer and subsequently withdrew it. Putting the XPATH expression inside the string() function returns "" if the expression evaluates to null. Makes sense.