phxnsharp / json-schema-tree

Example of a schema that declares a tree

Example of creating a JSON-Schema that defines a simple tree document.

The tree can have two types of leaf nodes (LeafA and LeafB), and two types of containers (ContainerA and ContainerB).

On main this is implemented by using an allOf constraint to represent the object hierarchy, and a disambiguator oneOf definition to allow one of the 4 types at any location in the tree.

On oneOf-anyOf this is implemented using a tricky nested structure of oneOf and anyOf keywords.

On use-if this is implemented using allOf and if statements.

Using the jschon Python implementation I tested these schemas. For a simple instance with 4 nodes that is invalid in a minor way (typo), it generates

• main: 379 lines of largely incomprehensible error messages.
• oneOf-anyOf: 716 lines of largely incomprehensible error messages.
• use-if: 46 lines of slightly less incomprehensible error messages.

The question is, how could this be implemented in a way that would produce better error messages?

The draft-next propertyDependencies keyword promises to help, but does not quite completely alleviate it. On the draft-next branch you can see what the schema might look like. Issues I had:

• I still have to write a qualifier before the propertyDependencies to ensure that the object is one of the proposed types and not something completely different. propertyDependencies currently succeeds if none of the branches are chosen.
• I want my tree to also have the ability to use a { "$ref":... } object instead of one of the proposed types. In order to do so I have to fall back on the old, noisy, *Of blocks, or use a complex if\then\else statement.