This is something me and my colleagues encounter from time to time.

The Problem

One of the problems of adding unique indexes to existing data, like adding the sluggable Doctrine behaviour using the StofDoctrineExtensionsBundle, is that the generated migration will end up throwing an error:

SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '' for key 'UNIQ_BDAFD8C8989D9B62'


Since the default values for the new MySQL column are not unique, adding the unique index is not possible – which is what the error above is telling us. So we will need to change the migration to also generate the unique values before adding the index.


In order to do so, we will have to split the generated migration into 2 different migrations, one for adding the new column, which could be a slug, and the other to add the unique index. After running the first migration, we need to execute the code that generates the unique values needed for the index. We can use the postUp method in a Doctrine migration to execute code after the “up” migration finished. We will also need to instantiate and boot the kernel in order to gain access to the Symfony framework and build our functionality like we would do in a controller:


For the second migration file we only add the code necessary to add/remove the unique indexes:

You can generate an empty migration file using the doctrine:migratios:generate command.

If you now run the doctrine:migrations:migrate command everything should be fine and the database should be populated with the unique values we needed in the first place.


Luckily I solved this issue before an important deadline. Let me know if you found any other way around it, or a quicker solution to this issue.

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