ios,iphone,sqlite,core-data , Change database of Live App without Data Lose
Change database of Live App without Data Lose
Question:
Tag: ios,iphone,sqlite,core-data
I want to update the database of my existing app(for new version) which is live on the app store. So I need to delete my existing database before using app or I can change the name of the database. After it If data exists in my old database I have to get all data and insert it again to my new sqlite file.
It looks like a slow process. My users don't want to loose data. Is there any other way from which I can easily change database of my Existing App without any data lose.
Answer:
First you need to detect that the database is the old one. One way of doing that is to have a metadata table with name/value text columns (value is a reserved word, so use a different column name) and keep the current schemaVersion in there. If this doesn't exist then you know it's the older version, but from now on you need to keep that schenaVersion up-to-date during these updates. You can keep other information about the database itself in that table.
If the database is fundamentally different then you need to use the second approach you suggest:
- Detect if old version of database, if not abort update.
- Create new database with temporary file name. This includes setting-up the new schema.
- Open both databases at once.
- Iterate through tables in old database and take any necessary values in order to populate tables in new database.
- Close both databases.
- Remove old database file and move new, temporary, database file to old, existing, name.
- Open database and proceed.
Alternatively, if the changes are not drastically different then you can use the ALTER TABLE statement to modify the schema. This is the much better approach as it leaves values in place if the columns are not removed from the schema.
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