Model conditional variants

[simontaurus]

Sometimes there's the need to express variant of a schema that apply under certain conditions.
Such variant may
A. only change the representation of the schema (e.g. display/hide fields, change labels, etc.)
B. actually change the schema (e.g. add fields or make additional fields mandatory)

JSON-SCHEMA provides the following options:

• >= Draft 7 Draft 2019-09:
  • dependentRequired: https://json-schema.org/understanding-json-schema/reference/conditionals#dependentRequired
  • dependentSchemas: https://json-schema.org/understanding-json-schema/reference/conditionals#dependentSchemas
• < Draft 2019-09
  • dependencies: https://json-schema.org/draft-07/draft-handrews-json-schema-validation-01#rfc.section.6.5.7
• > Draft 7:
  • if-then-else: https://json-schema.org/understanding-json-schema/reference/conditionals#ifthenelse
• < Draft 7:
  • https://json-schema.org/understanding-json-schema/reference/conditionals#implication
• oneOf: https://json-schema.org/understanding-json-schema/reference/combining#oneOf
  • in general needs a discriminator, see also: Proposal: Add propertyDependencies keyword (aka discriminator) json-schema-org/json-schema-spec#1082

Limitations of JSON-SCHEMA based tools:

• https://github.com/json-editor/json-editor
  • supports dependencies, if-then-else, and oneOf
  • if-then-else support is limited, especially regarding UI modifications (see if-then-else not working in allOf json-editor/json-editor#1440, if-then-else doesn't apply dynamically (at least to nested properties) json-editor/json-editor#1434)
• https://github.com/koxudaxi/datamodel-code-generator
  • supports only oneOf

Current recommendation is to use oneOf for both cases A and B. Once bugs in https://github.com/json-editor/json-editor are fixed, if-then-else is recommended for cases A