I am in a situation where I am having to choose whether I should Add/Update or Overwrite in a Daily Batch File Import into a Data Extension which I plan to use in Decision Paths in Journey through the contact data model (not journey data). Is it true that if my import type into this DE is Overwrite, it will cause issues as the _CustomObjectKey will change?

Also, can someone explain what _CustomObjectKey is? Does each DE record have a unique _CustomObjectKey or is it one per key per DE? How can we find the out _CustomObjectKey?

1 Answer 1


The hidden field _CustomObjectKey is an auto-incrementing value on each data extension. If you set the import type to overwrite it will have new _CustomObjectKey values.

For example, you have 3 records in a data extension. The _CustomObjectKey of those 3 records will be 1, 2, 3. You overwrite those records with 4 new records. Those _CustomObjectKey values will be 4, 5, 6, 7 even though it looks like the data extension only have 4 records. Each time you overwrite or add new records, that _CustomObjectKey value will automatically increment.

More information here: https://help.marketingcloud.com/en-US/documentation/exacttarget/subscribers/data_extensions_and_data_relationships/

With that said, I would recommend that you do not overwrite your data extension if you are planning to use Decision Splits in that journey. You can either:

  1. Use the import type of Add/Update
  2. Or import into a "staging" data extension and query into the data extension you use for your journey.

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