# Upserts & Identities
Its important to consider identities when using AshArchival _without_ a `base_filter` set up.
If you are using a `base_filter`, then all identities implicitly include that `base_filter` in their
`where` (handled by the data layer).
Take the following identities, for example:
```elixir
identities do
identity :unique_email, [:email], where: expr(is_nil(archived_at))
# and
identity :unique_email, [:email]
end
```
## With `is_nil(archived_at)`
Using this identity allows multiple archived records with the same email, but only one _non-archived_ record per email.
It enables reuse of archived email addresses for new active records, maintaining data integrity by preventing duplicate
active records while preserving archived data.
When you upsert a record using this identity, it will only consider active records.
## Without `is_nil(archived_at)`
This identity configuration enforces strict email uniqueness across all records. Once an email is used, it can't be used
again, even after that record is archived.
When you upsert a record using this identity, it will consider all records.