With the old fields in the `State` broken out we can now make `State` a
proper enum, replacing the nested `Status`. The naming with both `State`
and `Status` was a bit confusing.
Before, the entire state was stored as a JSON encoded blob including all
completed migrations. This commits moves the migrations into a dedicated
table, which prevents the encoded from growing indefinitely. The size of
the state probably wouldn't have become a problem but it feels weird for
a schema migration tool to not use a proper schema.
Next, the version stored in the state struct will be moved to a separate
key in the `reshape.data` table and `State` will become an enum with the
same structure as `Status`. The naming right now is a bit confusing.
Until now, using alter_column would cause indices to be lost as they
weren't copied to the temporary column. This fixes that for indices that
consist of one or more actual columns. It won't work for indices on
expressions.
Changing the default value only affects the new schema, the old schema
will still use the existing default value. This is to make sure a new
default value doesn't break the old application.
The builder will help simplify the tests and avoid boilerplate updates
when need fields are added to the create_table migration. We might want
to add builders all migrations later.
This checks for dangling temporary columns, triggers and function which
were used by migrations but should be removed once the migration has
been completed or aborted.
Previously, having multiple alter_column actions for a single column
could cause issues as the triggers and batch updates referenced the
wrong columns.
This commit also simplifies the batch update procedure. Rather than
running the actual update on existing rows, a NOP update will be
run which in turn will trigger the triggers to update the new temporary
columns.
