An indirect lookup relationship is used when an external object must relate to a standard or custom Salesforce object and the external data does not contain Salesforce record IDs. Salesforce requires the parent Salesforce object to contain a custom field marked External ID and Unique . Values from the external object ' s indirect lookup field are matched against this external ID field to establish the relationship. Salesforce specifically states that indirect lookups link a child external object to a parent standard or custom object using a custom unique External ID field. TEXT(Id) does not create such a relationship key, and CASESAFEID() merely converts Salesforce IDs to their 18-character representation. A normal Salesforce Record ID is used for standard lookup relationships, not indirect lookups.

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