Migration

Traditionally, an ORM tool performs migration to insert, delete and reshape user's tables and collections in the database. This requires manually creating migration instructions and doing the migration.

Teo thinks differently about this. Developers don't need to keep and organize a whole list of migration instructions. Teo utilizes the diff algorithm to handle database migrations automatically.

Auto migration

The auto migration performs the following things:

• Detecting deleted tables and delete them
• Detecting renamed tables and rename them
• Detecting newly created tables and create them
• For modified tables
  • Detecting deleted fields and indexes, delete them
  • Detecting renamed fields and indexes, rename them
  • Detecting newly created fields and indexes, create them
  • Detecting modified fields and indexes, try to modify them

Teo takes over the control of the database and delete unused tables. So be careful when migrating old projects with Teo.

Resolving conflicts

There are two main categories of conflicts.

New nonnull field is added to a table with existing records

If a nonnull field is added without a default value, an error will be thrown and the process will terminate. There are two ways to resolve this conflict.

Provide a migration default value

Add @migration(default: defaultValue) to the field.

model User {
    @id
    id: Int
    name: String
    @migration(default: "")
    nickname: String // new field
}

Drop the table if there are records

Add @migration(drop: true) to the model.

@migration(drop: true)
model User {
    @id
    id: Int
    name: String
    nickname: String // new field
}

Value of the old field type cannot transform into the new one

This conflict is when altering a field type of a column, and the new type cannot hold the value of current type. This type of conflict should be avoided.

Trigger auto migration

Use the migrate command to perform the migration.

Unless the command option --no-migration is provided, migration is automatically performed when HTTP server starts with the serve command.

Inspecting migration instructions

This feature will be available in the next new stable version.