Failed to generate schema with fields defined using dict

[nkonin]

Bug

• OS: macos Mojave 10.14.2
• Python version: 3.7.0 (default, Sep 18 2018, 18:47:08) [Clang 10.0.0 (clang-1000.10.43.1)]
• Pydantic version: 0.16

Code snippet:

import pydantic

class Example(pydantic.BaseModel):
    field: dict = None


Example.schema()

Expected:

In [5]: Example.schema()
Out[5]:
{'title': 'Example',
 'type': 'object',
 'properties': {'field': {'title': 'Field', 'type': 'object'}}}

Actually:

ValueError: Value not declarable with JSON Schema, field: field type=dict default=None

Traceback:

In [17]: Example.schema()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-17-dcbb076a11a6> in <module>
----> 1 Example.schema()

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/main.py in schema(cls, by_alias)
    334         if cached is not None:
    335             return cached
--> 336         s = model_schema(cls, by_alias=by_alias)
    337         cls._schema_cache[by_alias] = s
    338         return s

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in model_schema(model, by_alias, ref_prefix)
    189     model_name_map = get_model_name_map(flat_models)
    190     m_schema, m_definitions = model_process_schema(
--> 191         model, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
    192     )
    193     if m_definitions:

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in model_process_schema(model, by_alias, model_name_map, ref_prefix)
    455         s['description'] = clean_docstring(model.__doc__)
    456     m_schema, m_definitions = model_type_schema(
--> 457         model, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
    458     )
    459     s.update(m_schema)

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in model_type_schema(model, by_alias, model_name_map, ref_prefix)
    476     for k, f in model.__fields__.items():
    477         f_schema, f_definitions = field_schema(
--> 478             f, by_alias=by_alias, model_name_map=model_name_map, ref_prefix=ref_prefix
    479         )
    480         definitions.update(f_definitions)

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in field_schema(field, by_alias, model_name_map, ref_prefix)
    236         model_name_map=model_name_map,
    237         schema_overrides=schema_overrides,
--> 238         ref_prefix=ref_prefix,
    239     )
    240     # $ref will only be returned when there are no schema_overrides

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in field_type_schema(field, by_alias, model_name_map, schema_overrides, ref_prefix)
    434             model_name_map=model_name_map,
    435             schema_overrides=schema_overrides,
--> 436             ref_prefix=ref_prefix,
    437         )
    438         definitions.update(f_definitions)

~/Documents/projects/broker.nosync/mf_credit_back/venv/lib/python3.7/site-packages/pydantic/schema.py in field_singleton_schema(field, by_alias, model_name_map, schema_overrides, ref_prefix)
    632         else:
    633             return sub_schema, definitions
--> 634     raise ValueError(f'Value not declarable with JSON Schema, field: {field}')
    635
    636

ValueError: Value not declarable with JSON Schema, field: field type=dict default=None

[samuelcolvin]

fixed in #331.