Literal annotation does not render type to json-schema #8905
Description
Initial Checks
- I confirm that I'm using Pydantic V2
Description
When defining a property as Literal, eg:
from pydantic import BaseModel
from typing import Literal
class Foo(BaseModel):
bar: Literal["Bar"] = 'Bar'
baz: Literal[None] = NoneThe output json-schema model loses the typing of the variable used for the literal. I.e.:
{
"properties": {
"bar": {
"const": "Bar",
"default": "Bar",
"title": "Bar"
},
"baz": {
"const": null,
"default": null,
"title": "Baz"
}
},
"title": "Foo",
"type": "object"
}
It would be nice to infer this type and correctly add it to the schema. This could be achieved by simply extending the literal_schema method
pydantic/pydantic/json_schema.py
Line 722 in 9811727
with:
def literal_schema(self, schema: core_schema.LiteralSchema) -> JsonSchemaValue:
"""Generates a JSON schema that matches a literal value.
Args:
schema: The core schema.
Returns:
The generated JSON schema.
"""
expected = [v.value if isinstance(v, Enum) else v for v in schema["expected"]]
# jsonify the expected values
expected = [to_jsonable_python(v) for v in expected]
types = {type(e) for e in expected}
if len(expected) == 1:
if isinstance(expected[0], str):
return {"const": expected[0], "type": "string"}
elif isinstance(expected[0], int):
return {"const": expected[0], "type": "integer"}
elif isinstance(expected[0], float):
return {"const": expected[0], "type": "number"}
elif isinstance(expected[0], bool):
return {"const": expected[0], "type": "boolean"}
elif isinstance(expected[0], list):
return {"const": expected[0], "type": "array"}
elif expected[0] is None:
return {"const": expected[0], "type": "null"}
else:
return {"const": expected[0]}
if types == {str}:
return {"enum": expected, "type": "string"}
elif types == {int}:
return {"enum": expected, "type": "integer"}
elif types == {float}:
return {"enum": expected, "type": "number"}
elif types == {bool}:
return {"enum": expected, "type": "boolean"}
elif types == {list}:
return {"enum": expected, "type": "array"}
# there is not None case because if it's mixed it hits the final `else`
# if it's a single Literal[None] then it becomes a `const` schema above
else:
return {"enum": expected}Example Code
No response
Python, Pydantic & OS Version
pydantic version: 2.5.3
pydantic-core version: 2.14.6
pydantic-core build: profile=release pgo=true
install path: <...>\.venv\Lib\site-packages\pydantic
python version: 3.11.7 (tags/v3.11.7:fa7a6f2, Dec 4 2023, 19:24:49) [MSC v.1937 64 bit (AMD64)]
platform: Windows-10-10.0.19045-SP0
related packages: typing_extensions-4.9.0