In my last post I talked about setting up Symfony2 entities for translation and integrating it with Sonata Admin. One of the trickier parts of moving from a non-translatable entity to a translatable one is the migration of your data.
To understand some of the complexities with the migration you must understand the changes to the database that occur when taking an entity from being a regular entity to a translatable one. Any columns that are translatable will now live on a separate table and the old column is no longer used. Let’s use the following pre-translation entity DB schema as an example:
For this entity we’ll make visible_label translatable, following the instructions in my previous post. This will result in the following final schema:
The column “visible_label” has moved from the regular entity table to the entity’s translation table. If you had data in the visible_label previously it would be lost as that column no longer exists. Since we had tons of data in our case this wasn’t acceptable.
To make sure we didn’t lose data, we did the translatable migration in two stages. First, we kept the columns we were translating in the original entity and only removed the getters and setters. The reason we removed the getter and setters is we wanted to utilize the magic __call() method so it would return values from the translatable entity. All that was left was the original column declaration. At first it seemed like making the column variable public for the time being would be a quick and easy solution, then run a script that reads the public variable and migrates it to the translation. The problem with this approach is Twig will read out the public variable rather than calling through the __call() method to the translatable entity. Since we were testing at the same time as trying to build the migration, we needed the tests to access the translatable entity and not the old public variable. We ended up using Reflection Classes and keeping the column declared as a private. With reflection you can change properties to be accessible outside of the class even though they are declared private. For example:
By using the reflection we’re able to access the original “visible_label” column and migrate the data to the translation entity. We built similar routines for each of the entities that we had to migrate. After the migration and everyone confirmed that the live site was functioning properly, we removed the translated columns from the original entity and database.
By taking this two staged approach we were able to move to translatable entities while not losing any data in the migration. In our case we also marked (//START TRANS, //END TRANS) on each entity the start of translatable columns and end so that we could use sed to go through all of them and remove the old columns once the migration was finished.
Happy translating!