DB Migration

When upgrading the database, there is a risk of data loss, such as when deleting an old field. Luckily, Casdoor utilizes xorm, which assists with many database migration problems. However, some schema and data migrations must still be handled manually, such as when a field name is changed.

note

Refer to the xorm docs for a better understanding of xorm's schema operations.

How it Works

As mentioned earlier, xorm is unable to handle field name changes. To address this, xorm provides a migrate package that can assist with this problem.

To handle field renaming, you can write code like this:

migrations := []*migrate.Migration{
        {
            ID: "CasbinRule--fill ptype field with p",
            Migrate: func(tx *xorm.Engine) error {
                _, err := tx.Cols("ptype").Update(&xormadapter.CasbinRule{
                    Ptype: "p",
                })
                return err
            },
            Rollback: func(tx *xorm.Engine) error {
                return tx.DropTables(&xormadapter.CasbinRule{})
            },
        },
    }
    m.Migrate()

Our objective is to rename p_type to ptype. However, since xorm does not support field renaming, we must resort to a more intricate approach: assigning the value of p_type to ptype, and subsequently deleting the p_type field.

The ID field uniquely identifies the migration being performed. After m.Migrate() runs, the value of ID will be added to the migrations table of the database.

Upon starting the project again, the database will check for any existing ID field in the table and refrain from performing any operations associated with the same ID.