Exam Certified Platform App Builder topic 1 question 550 discussion

Answer is A https://developer.salesforce.com/forums/?id=906F0000000DCbOIAW 'If you convert an auto-number field into a text field, the data in that field remains unchanged. Also, you can safely convert a text custom field into an auto-number field without losing your data. Converting an auto-number field into any other data type results in data loss. Auto-number fields can contain a maximum of 30 characters. Before converting a text custom field into an auto-number field, change any records that contain more than 30 characters in that field.'

Correct answer is D. D. Create a Text field for the original Invoice Number and an AutoNumber field for the Salesforce Invoice Number: By creating two separate fields, you can preserve the existing Invoice Numbers from the external system and still use Salesforce’s AutoNumber functionality to ensure new Invoice records have unique numbers. The Text field can store the original invoice numbers from the external system, while the AutoNumber field automatically generates unique numbers for new invoices created in Salesforce.

It should be A, coz it clearly states in the question 'After the migration, each new Invoice created in Salesforce must have a unique Invoice Number.' whereas unique external id won't populate automatically and mainly used for matching.

A "Also, you can safely convert a text custom field into an auto-number field without losing your data."

In the case of answer A, I think that changing from text type to automatic numbering type will cause data loss

C. Create a Text field and mark it as a unique external ID field. All other answers don't make sense.

A. Create a Text field, then change it to AutoNumber after the migration. This option allows the app builder to first migrate the existing Invoice Numbers from the external system, which would be stored in a text field, and then change the field type to an AutoNumber after the migration. This ensures that the existing Invoice Numbers are preserved, and that each new Invoice created in Salesforce will have a unique Invoice Number generated by the AutoNumber field.