[Python] Resolving $ref $defs to get properties from Pydantic model_jason_schema

I'm using a library that utilizes Pydantic v2 and .model_json_schema()['properties'] to pull information and metadata about the class properties (like those set by Field json_schema_extra). I've found the library fails when you build a class with an optional self reference because ['properties'] in the json schema becomes a key within the '#/$defs/' dictionary, pointed to by $ref.

Is the following function the most efficient/direct way to pull the ['properties'] dictionary from the Pydantic class?

def resolve_ref(schema, ref_value):
"""
Resolves a JSON Schema $ref to a definition within the same schema.

Args:
schema (dict): The JSON Schema dictionary.
ref_value (str): The $ref value (e.g., "#/$defs/myDef").

Returns:
dict: The resolved schema definition, or None if not found.
"""

if not ref_value.startswith("#/$defs/"):
return None # Not a defs reference

def_path = ref_value[len("#/$defs/"):] # Extract the definition name
if schema.get("$defs") and def_path in schema["$defs"]:
return schema["$defs"][def_path]
return None # Definition not found


Example classes and code:

import pydantic
from typing import ClassVar, List, Optional

from pydantic import Field, BaseModel

class Node(BaseModel):
myprop: str
children: Optional["FailingNode"] = None

class FailingNode(BaseModel):
myprop: str
children: Optional["FailingNode"] = None

def resolve_ref(schema, ref_value):
""" (as above) """
...

if __name__ == "__main__":
good = Node(myprop="good")
goodschema = good.model_json_schema()
print(goodschema['properties'].keys())

bad = FailingNode(myprop="bad")
badschema = bad.model_json_schema()

assert 'properties' not in badschema.keys()
resolved = resolve_ref(badschema, badschema['$ref'])
print(resolved['properties'].keys())

Continue reading...