## Problem:
In PR #11887, a bug fix for `copyToLocale` was introduced to address
issues with copying content between locales in Postgres. However, an
incorrect algorithm was used, which removed all "id" properties from
documents being copied. This led to bug #12536, where `copyToLocale`
would mistakenly delete the document in the source language, affecting
not only Postgres but any database.
## Cause and Solution:
When copying documents with localized arrays or blocks, Postgres throws
errors if there are two blocks with the same ID. This is why PR #11887
removed all IDs from the document to avoid conflicts. However, this
removal was too broad and caused issues in cases where it was
unnecessary.
The correct solution should remove the IDs only in nested fields whose
ancestors are localized. The reasoning is as follows:
- When an array/block is **not localized** (`localized: false`), if it
contains localized fields, these fields share the same ID across
different locales.
- When an array/block **is localized** (`localized: true`), its
descendant fields cannot share the same ID across different locales if
Postgres is being used. This wouldn't be an issue if the table
containing localized blocks had a composite primary key of `locale +
id`. However, since the primary key is just `id`, we need to assign a
new ID for these fields.
This PR properly removes IDs **only for nested fields** whose ancestors
are localized.
Fixes#12536
## Example:
### Before Fix:
```js
// Original document (en)
array: [{
id: "123",
text: { en: "English text" }
}]
// After copying to 'es' locale, a new ID was created instead of updating the existing item
array: [{
id: "456", // 🐛 New ID created!
text: { es: "Spanish text" } // 🐛 'en' locale is missing
}]
```
### After fix:
```js
// After fix
array: [{
id: "123", // ✅ Same ID maintained
text: {
en: "English text",
es: "Spanish text" // ✅ Properly merged with existing item
}
}]
```
## Additional fixes:
### TraverseFields
In the process of designing an appropriate solution, I detected a couple
of bugs in traverseFields that are also addressed in this PR.
### Fixed MongoDB Empty Array Handling
During testing, I discovered that MongoDB and PostgreSQL behave
differently when querying documents that don't exist in a specific
locale:
- PostgreSQL: Returns the document with data from the fallback locale
- MongoDB: Returns the document with empty arrays for localized fields
This difference caused `copyToLocale` to fail in MongoDB because the
merge algorithm only checked for `null` or `undefined` values, but not
empty arrays. When MongoDB returned `content: []` for a non-existent
locale, the algorithm would attempt to iterate over the empty array
instead of using the source locale's data.
### Move test e2e to int
The test introduced in #11887 didn't catch the bug because our e2e suite
doesn't run on Postgres. I migrated the test to an integration test that
does run on Postgres and MongoDB.
4a712b3483