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Purpose
In Salesforce you may sometimes find the need to create a custom formula field in order to return specific data from a Child Object.
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A formula that returns related fields from a Child Object may look like this:
“Case__r.CaseNumber”
This would return the Case Number of the related Child Case object.
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Also, please note that a custom "relationship" field ends in "__r" and not "__c" as most custom fields.
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Answer
Although the connector does support custom fields, it does not support custom "relationship" fields.
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Custom fields whose API names end in "__c" are standard custom fields whose values pulled directly from the parent record which the connector is able to provide to Jira without issues.
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Custom fields whose API names end in "__r" are custom "relationship" fields.
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These fields cannot be synched as the field where the information is being pulled is a field from a different object altogether and not part of the current associated field.
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