DB Migration

When the database is upgraded, it is easy to have a data crash, for example, we need to delete an old field. Fortunately, the xorm used by Casdoor will help us with a lot of database migration problems. But we still need to handle some schema and data migrations ourselves, such as a field name changed

note

You can understand xorm Schema operation in xorm docs

How it works

As mentioned above, when a field name changes, xorm will not be able to do anything, but xorm provides a migrate package to help us solve this problem.

You can write code like this to handle field renaming:

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()

What we want to achieve is: rename p_type to ptype. But since xorm does not support field renaming, we can only use a more complicated way: assign the value of p_type to ptype, and then delete the p_type field.

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

When the project is started again, the database will check the existing ID field in the table and will not perform operations with the same ID