Migrations

The synchronization between Entities definition files and actual tables in the database is handled by the MikroORM's migrations system.

Indeed, in order to apply on the database all the changes of your Entities classes, you must generate migrations JS files. They contain all the SQL statements needed to modify the current database state in order to match with the newly modified Entities classes, without losing any data.

tip

Migration files should be versioned as it permit to rollback to a certain state of your database.

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To generate a migration file, simply do this command in the root of your project:

npm run migration:create

Then, to apply it to the database:

npm run migration:up

Troubleshooting

When using SQLite, if you encounter this error:

SQLITE_ERROR: Cannot add a NOT NULL column with default value NULL

It means that you are trying to add a column without any default value to an already existing table.
It is a behavior inherent to SQLite.

In order to fix this, you should define a default value in the options of the @Property() decorator like this:

    @Property({ default: 'John Doe' })
    name: string

as explained in more details here and here.