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Changes between Initial Version and Version 1 of Ticket #26819, comment 15

initial	v1
1	1	This happens only for Inline admin models (only `validate_unique()` of `BaseModelFormSet` contains the problematic code).
2	2
3		This is not limited to `ArrayField`; any custom field may be affected. In our case, the `phonenumber_field.modelfields.PhoneNumberField` is causing the error `unhashable type: 'PhoneNumber'`. Since Django documentation does not mandate that custom fields are hashable (i.e., define the `__hash__()` method), I suppose that most of the existing non-builtin fields are affected.
	3	This is not related to the database and is purely a Python issue. This is not limited to `ArrayField`; any custom field may be affected. In our case, the `phonenumber_field.modelfields.PhoneNumberField` is causing the error `unhashable type: 'PhoneNumber'`. Since Django documentation does not mandate that custom fields are hashable (i.e., define the `__hash__()` method), I suppose that most of the existing non-builtin fields are affected.
4	4
5	5	Looks like the solution is either to keep `seen_data` as a `set()` and rely on some property of the field (unreliable and error-prone, see sample code below), or give up `set()` and manually implement removal of duplicates.