Add a new optional or required property, remove a property

Adding a new property does not require a migration transform document, it can be achieved by simply adding the property to the schema, if a new required property is added, then the default value for that property will be the default value for the property type, e.g. 0 for numeric types, an empty string for string types, false for boolean types.

If the property type does not have a sensible default (e.g. it is a non-null enum property, or non-null complex property), then a migration document may be provided to populate the new property.

When a property is deleted, the original value is captured in a post-migration column on the original table, with all constraints removed.

For example, given this initial schema:

MySchema:
  type: object
  version: 1
  properties:
    unchanged:
      type: string
    deleted:
      type: string

The following updated schema:

MySchema:
  type: object
  version: 2
  properties:
    unchanged:
      type: string
    deleted:
      type: string
    addedOptional:
      type: string
    addedRequired:
      type: string!
    addedCustom:
      type: string!

The following migration document:

- target: MySchema
  fromVersion: 1
  toVersion: 2
  properties:
    addedCustom: "'default value'"

And the following initial row:

unchanged	deleted
"staying"	"going"

Then after a successful migration with migration id m1, the row will be as follows:

unchanged	addedOptional	addedRequired	addedCustom	_going_m1
"staying"	(null)	""	"defaultValue"	"going"

Note: The _going_m1 column will be set to nullable if the target storage supports constraints, and regardless of the original nullability of this property.