Salesforce sfdx:data:tree:export for objects with lookups

Question

We have a list of MyCustomObject__c which have a Master/Detail relationship with Account and we set on the Account a reference to the last of MyCustomObject__c, which we call Last_MyCustomObject__c.

When we try to export the data using `sfdx force:data:tree:export -p -q myquery.txt" the export fails saying reference MyCustomObject__c not found for Last_MyCustomObject__c. What is the right way get this data so it can be imported into a scratch org?

Ideally if we would write a query that would be like

Select ID, Name, Last_MyCustomObject__c from Account

or

Select ID, Name, Last_MyCustomObject__c, (Select Id, Name from MyCustomObject__c where Id = Last_MyCustomObject__c ) from Account.

Additionally, if we want to import other objects related to the same Account, how can we do that, if it will not be possible to express the export in a single query?

Answer 1

You have to start at the top of the tree to get the whole record. So if you only want the one MyCustomObject__c record that is represented by the Last_MyCustomObject__c lookup, you have to sort of recreate the behavior in your query:

Select ID, Name, Last_MyCustomObject__c, 
      (Select Id, Name from MyCustomObjects__r ORDER BY CreatedDate DESC LIMIT 1) 
  From Account