diff --git a/pydantic/schema.py b/pydantic/schema.py
--- a/pydantic/schema.py
+++ b/pydantic/schema.py
@@ -419,10 +419,13 @@ def get_flat_models_from_field(field: ModelField, known_models: TypeModelSet) ->
     # Handle dataclass-based models
     if is_builtin_dataclass(field.type_):
         field.type_ = dataclass(field.type_)
+        was_dataclass = True
+    else:
+        was_dataclass = False
     field_type = field.type_
     if lenient_issubclass(getattr(field_type, '__pydantic_model__', None), BaseModel):
         field_type = field_type.__pydantic_model__
-    if field.sub_fields and not lenient_issubclass(field_type, BaseModel):
+    if field.sub_fields and (not lenient_issubclass(field_type, BaseModel) or was_dataclass):
         flat_models |= get_flat_models_from_fields(field.sub_fields, known_models=known_models)
     elif lenient_issubclass(field_type, BaseModel) and field_type not in known_models:
         flat_models |= get_flat_models_from_model(field_type, known_models=known_models)

diff --git a/tests/test_schema.py b/tests/test_schema.py
--- a/tests/test_schema.py
+++ b/tests/test_schema.py
@@ -2884,3 +2884,34 @@ class Model(BaseModel):
             },
         },
     }
+
+
+def test_nested_python_dataclasses():
+    """
+    Test schema generation for nested python dataclasses
+    """
+
+    from dataclasses import dataclass as python_dataclass
+
+    @python_dataclass
+    class ChildModel:
+        name: str
+
+    @python_dataclass
+    class NestedModel:
+        child: List[ChildModel]
+
+    assert model_schema(dataclass(NestedModel)) == {
+        'title': 'NestedModel',
+        'type': 'object',
+        'properties': {'child': {'title': 'Child', 'type': 'array', 'items': {'$ref': '#/definitions/ChildModel'}}},
+        'required': ['child'],
+        'definitions': {
+            'ChildModel': {
+                'title': 'ChildModel',
+                'type': 'object',
+                'properties': {'name': {'title': 'Name', 'type': 'string'}},
+                'required': ['name'],
+            }
+        },
+    }

list of python dataclass broken after upgrade to 1.9.0
### Checks

* [x] I added a descriptive title to this issue
* [x] I have searched (google, github) for similar issues and couldn't find anything
* [x] I have read and followed [the docs](https://pydantic-docs.helpmanual.io/) and still think this is a bug

<!-- Sorry to sound so draconian, but every second saved replying to issues is time spend improving pydantic :-) -->

# Bug

Output of `python -c "import pydantic.utils; print(pydantic.utils.version_info())"`:
```
            pydantic version: 1.9.0
            pydantic compiled: True
                 install path: my_directory/venv/lib/python3.8/site-packages/pydantic
               python version: 3.8.6 (default, Sep  6 2021, 17:04:40)  [GCC 10.3.0]
                     platform: Linux-5.13.0-28-generic-x86_64-with-glibc2.33
     optional deps. installed: ['typing-extensions']
```
<!-- or if you're using pydantic prior to v1.3, manually include: OS, python version and pydantic version -->

<!-- Please read the [docs](https://pydantic-docs.helpmanual.io/) and search through issues to
confirm your bug hasn't already been reported. -->

<!-- Where possible please include a self-contained code snippet describing your bug: -->

The following snippet works as expected with version 1.8.2 but errors with version 1.9.0

```py
from dataclasses import dataclass
from typing import List
import pydantic


@dataclass()
class A:
    a: int = 5


@dataclass()
class B_and_As:
    list_of_as: List[A]
    b: str = 'b'


def get_schema(json_cls: dataclass):
    as_pydantic = pydantic.dataclasses.dataclass(json_cls)
    schema = as_pydantic.__pydantic_model__.schema()
    print(schema)


get_schema(B_and_As)
```

error:
```
    schema = as_pydantic.__pydantic_model__.schema()
  File "pydantic/main.py", line 647, in pydantic.main.BaseModel.schema
  File "pydantic/schema.py", line 185, in pydantic.schema.model_schema
  File "pydantic/schema.py", line 617, in pydantic.schema.model_process_schema
  File "pydantic/schema.py", line 658, in pydantic.schema.model_type_schema
  File "pydantic/schema.py", line 258, in pydantic.schema.field_schema
  File "pydantic/schema.py", line 498, in pydantic.schema.field_type_schema
  File "pydantic/schema.py", line 848, in pydantic.schema.field_singleton_schema
  File "pydantic/schema.py", line 736, in pydantic.schema.field_singleton_sub_fields_schema
  File "pydantic/schema.py", line 563, in pydantic.schema.field_type_schema
  File "pydantic/schema.py", line 947, in pydantic.schema.field_singleton_schema
ValueError: Value not declarable with JSON Schema, field: name='_list_of_as' type=A required=True
```

on 1.8.2 it's prints as expected:
```
{'title': 'B_and_As', 'type': 'object', 'properties': {'list_of_as': {'title': 'List Of As', 'type': 'array', 'items': {'$ref': '#/definitions/A'}}, 'b': {'title': 'B', 'default': 'b', 'type': 'string'}}, 'required': ['list_of_as'], 'definitions': {'A': {'title': 'A', 'type': 'object', 'properties': {'a': {'title': 'A', 'default': 5, 'type': 'integer'}}}}}
```


Btw:
* `get_schema(A)` works in both versions
* [Discussed on stackoverflow](https://stackoverflow.com/questions/71048746/how-can-i-generate-json-schema-for-list-of-dataclass-with-pydantic)

tests/test_schema.py::test_nested_python_dataclasses
tests/test_schema.py::test_key tests/test_schema.py::test_by_alias tests/test_schema.py::test_ref_template tests/test_schema.py::test_by_alias_generator tests/test_schema.py::test_sub_model tests/test_schema.py::test_schema_class tests/test_schema.py::test_schema_repr tests/test_schema.py::test_schema_class_by_alias tests/test_schema.py::test_choices tests/test_schema.py::test_enum_modify_schema tests/test_schema.py::test_enum_schema_custom_field tests/test_schema.py::test_enum_and_model_have_same_behaviour tests/test_schema.py::test_enum_includes_extra_without_other_params tests/test_schema.py::test_list_enum_schema_extras tests/test_schema.py::test_json_schema tests/test_schema.py::test_list_sub_model tests/test_schema.py::test_optional tests/test_schema.py::test_any tests/test_schema.py::test_set tests/test_schema.py::test_const_str tests/test_schema.py::test_const_false tests/test_schema.py::test_tuple[tuple-extra_props0] tests/test_schema.py::test_tuple[field_type1-extra_props1] tests/test_schema.py::test_tuple[field_type2-extra_props2] tests/test_schema.py::test_tuple[field_type3-extra_props3] tests/test_schema.py::test_deque tests/test_schema.py::test_bool tests/test_schema.py::test_strict_bool tests/test_schema.py::test_dict tests/test_schema.py::test_list tests/test_schema.py::test_list_union_dict[field_type0-expected_schema0] tests/test_schema.py::test_list_union_dict[field_type1-expected_schema1] tests/test_schema.py::test_list_union_dict[field_type2-expected_schema2] tests/test_schema.py::test_list_union_dict[field_type3-expected_schema3] tests/test_schema.py::test_list_union_dict[field_type4-expected_schema4] tests/test_schema.py::test_date_types[datetime-expected_schema0] tests/test_schema.py::test_date_types[date-expected_schema1] tests/test_schema.py::test_date_types[time-expected_schema2] tests/test_schema.py::test_date_types[timedelta-expected_schema3] tests/test_schema.py::test_str_basic_types[field_type0-expected_schema0] tests/test_schema.py::test_str_basic_types[field_type1-expected_schema1] tests/test_schema.py::test_str_basic_types[field_type2-expected_schema2] tests/test_schema.py::test_str_basic_types[field_type3-expected_schema3] tests/test_schema.py::test_str_constrained_types[StrictStr-expected_schema0] tests/test_schema.py::test_str_constrained_types[ConstrainedStr-expected_schema1] tests/test_schema.py::test_str_constrained_types[ConstrainedStrValue-expected_schema2] tests/test_schema.py::test_special_str_types[AnyUrl-expected_schema0] tests/test_schema.py::test_special_str_types[UrlValue-expected_schema1] tests/test_schema.py::test_email_str_types[EmailStr-email] tests/test_schema.py::test_email_str_types[NameEmail-name-email] tests/test_schema.py::test_secret_types[SecretBytes-string] tests/test_schema.py::test_secret_types[SecretStr-string] tests/test_schema.py::test_special_int_types[ConstrainedInt-expected_schema0] tests/test_schema.py::test_special_int_types[ConstrainedIntValue-expected_schema1] tests/test_schema.py::test_special_int_types[ConstrainedIntValue-expected_schema2] tests/test_schema.py::test_special_int_types[ConstrainedIntValue-expected_schema3] tests/test_schema.py::test_special_int_types[PositiveInt-expected_schema4] tests/test_schema.py::test_special_int_types[NegativeInt-expected_schema5] tests/test_schema.py::test_special_int_types[NonNegativeInt-expected_schema6] tests/test_schema.py::test_special_int_types[NonPositiveInt-expected_schema7] tests/test_schema.py::test_special_float_types[ConstrainedFloat-expected_schema0] tests/test_schema.py::test_special_float_types[ConstrainedFloatValue-expected_schema1] tests/test_schema.py::test_special_float_types[ConstrainedFloatValue-expected_schema2] tests/test_schema.py::test_special_float_types[ConstrainedFloatValue-expected_schema3] tests/test_schema.py::test_special_float_types[PositiveFloat-expected_schema4] tests/test_schema.py::test_special_float_types[NegativeFloat-expected_schema5] tests/test_schema.py::test_special_float_types[NonNegativeFloat-expected_schema6] tests/test_schema.py::test_special_float_types[NonPositiveFloat-expected_schema7] tests/test_schema.py::test_special_float_types[ConstrainedDecimal-expected_schema8] tests/test_schema.py::test_special_float_types[ConstrainedDecimalValue-expected_schema9] tests/test_schema.py::test_special_float_types[ConstrainedDecimalValue-expected_schema10] tests/test_schema.py::test_special_float_types[ConstrainedDecimalValue-expected_schema11] tests/test_schema.py::test_uuid_types[UUID-uuid] tests/test_schema.py::test_uuid_types[UUID1-uuid1] tests/test_schema.py::test_uuid_types[UUID3-uuid3] tests/test_schema.py::test_uuid_types[UUID4-uuid4] tests/test_schema.py::test_uuid_types[UUID5-uuid5] tests/test_schema.py::test_path_types[FilePath-file-path] tests/test_schema.py::test_path_types[DirectoryPath-directory-path] tests/test_schema.py::test_path_types[Path-path] tests/test_schema.py::test_json_type tests/test_schema.py::test_ipv4address_type tests/test_schema.py::test_ipv6address_type tests/test_schema.py::test_ipvanyaddress_type tests/test_schema.py::test_ipv4interface_type tests/test_schema.py::test_ipv6interface_type tests/test_schema.py::test_ipvanyinterface_type tests/test_schema.py::test_ipv4network_type tests/test_schema.py::test_ipv6network_type tests/test_schema.py::test_ipvanynetwork_type tests/test_schema.py::test_callable_type[type_0-default_value0] tests/test_schema.py::test_callable_type[type_1-<lambda>] tests/test_schema.py::test_callable_type[type_2-default_value2] tests/test_schema.py::test_callable_type[type_3-<lambda>] tests/test_schema.py::test_error_non_supported_types tests/test_schema.py::test_flat_models_unique_models tests/test_schema.py::test_flat_models_with_submodels tests/test_schema.py::test_flat_models_with_submodels_from_sequence tests/test_schema.py::test_model_name_maps tests/test_schema.py::test_schema_overrides tests/test_schema.py::test_schema_overrides_w_union tests/test_schema.py::test_schema_from_models tests/test_schema.py::test_schema_with_refs[#/components/schemas/-None] tests/test_schema.py::test_schema_with_refs[None-#/components/schemas/{model}] tests/test_schema.py::test_schema_with_refs[#/components/schemas/-#/{model}/schemas/] tests/test_schema.py::test_schema_with_custom_ref_template tests/test_schema.py::test_schema_ref_template_key_error tests/test_schema.py::test_schema_no_definitions tests/test_schema.py::test_list_default tests/test_schema.py::test_enum_str_default tests/test_schema.py::test_enum_int_default tests/test_schema.py::test_dict_default tests/test_schema.py::test_constraints_schema[kwargs0-str-expected_extra0] tests/test_schema.py::test_constraints_schema[kwargs1-ConstrainedStrValue-expected_extra1] tests/test_schema.py::test_constraints_schema[kwargs2-str-expected_extra2] tests/test_schema.py::test_constraints_schema[kwargs3-bytes-expected_extra3] tests/test_schema.py::test_constraints_schema[kwargs4-str-expected_extra4] tests/test_schema.py::test_constraints_schema[kwargs5-int-expected_extra5] tests/test_schema.py::test_constraints_schema[kwargs6-int-expected_extra6] tests/test_schema.py::test_constraints_schema[kwargs7-int-expected_extra7] tests/test_schema.py::test_constraints_schema[kwargs8-int-expected_extra8] tests/test_schema.py::test_constraints_schema[kwargs9-int-expected_extra9] tests/test_schema.py::test_constraints_schema[kwargs10-float-expected_extra10] tests/test_schema.py::test_constraints_schema[kwargs11-float-expected_extra11] tests/test_schema.py::test_constraints_schema[kwargs12-float-expected_extra12] tests/test_schema.py::test_constraints_schema[kwargs13-float-expected_extra13] tests/test_schema.py::test_constraints_schema[kwargs14-float-expected_extra14] tests/test_schema.py::test_constraints_schema[kwargs15-float-expected_extra15] tests/test_schema.py::test_constraints_schema[kwargs16-float-expected_extra16] tests/test_schema.py::test_constraints_schema[kwargs17-float-expected_extra17] tests/test_schema.py::test_constraints_schema[kwargs18-float-expected_extra18] tests/test_schema.py::test_constraints_schema[kwargs19-Decimal-expected_extra19] tests/test_schema.py::test_constraints_schema[kwargs20-Decimal-expected_extra20] tests/test_schema.py::test_constraints_schema[kwargs21-Decimal-expected_extra21] tests/test_schema.py::test_constraints_schema[kwargs22-Decimal-expected_extra22] tests/test_schema.py::test_constraints_schema[kwargs23-Decimal-expected_extra23] tests/test_schema.py::test_unenforced_constraints_schema[kwargs0-int] tests/test_schema.py::test_unenforced_constraints_schema[kwargs1-float] tests/test_schema.py::test_unenforced_constraints_schema[kwargs2-Decimal] tests/test_schema.py::test_unenforced_constraints_schema[kwargs3-bool] tests/test_schema.py::test_unenforced_constraints_schema[kwargs4-int] tests/test_schema.py::test_unenforced_constraints_schema[kwargs5-str] tests/test_schema.py::test_unenforced_constraints_schema[kwargs6-bytes] tests/test_schema.py::test_unenforced_constraints_schema[kwargs7-str] tests/test_schema.py::test_unenforced_constraints_schema[kwargs8-bool] tests/test_schema.py::test_unenforced_constraints_schema[kwargs9-type_9] tests/test_schema.py::test_unenforced_constraints_schema[kwargs10-type_10] tests/test_schema.py::test_unenforced_constraints_schema[kwargs11-ConstrainedListValue] tests/test_schema.py::test_unenforced_constraints_schema[kwargs12-ConstrainedSetValue] tests/test_schema.py::test_unenforced_constraints_schema[kwargs13-ConstrainedFrozenSetValue] tests/test_schema.py::test_constraints_schema_validation[kwargs0-str-foo] tests/test_schema.py::test_constraints_schema_validation[kwargs1-str-foo] tests/test_schema.py::test_constraints_schema_validation[kwargs2-bytes-foo] tests/test_schema.py::test_constraints_schema_validation[kwargs3-str-foo] tests/test_schema.py::test_constraints_schema_validation[kwargs4-int-3] tests/test_schema.py::test_constraints_schema_validation[kwargs5-int-3] tests/test_schema.py::test_constraints_schema_validation[kwargs6-int-3] tests/test_schema.py::test_constraints_schema_validation[kwargs7-int-2] tests/test_schema.py::test_constraints_schema_validation[kwargs8-int-3] tests/test_schema.py::test_constraints_schema_validation[kwargs9-int-3] tests/test_schema.py::test_constraints_schema_validation[kwargs10-int-5] tests/test_schema.py::test_constraints_schema_validation[kwargs11-float-3.0] tests/test_schema.py::test_constraints_schema_validation[kwargs12-float-2.1] tests/test_schema.py::test_constraints_schema_validation[kwargs13-float-3.0] tests/test_schema.py::test_constraints_schema_validation[kwargs14-float-4.9] tests/test_schema.py::test_constraints_schema_validation[kwargs15-float-3.0] tests/test_schema.py::test_constraints_schema_validation[kwargs16-float-2.0] tests/test_schema.py::test_constraints_schema_validation[kwargs17-float-3.0] tests/test_schema.py::test_constraints_schema_validation[kwargs18-float-5.0] tests/test_schema.py::test_constraints_schema_validation[kwargs19-float-3] tests/test_schema.py::test_constraints_schema_validation[kwargs20-float-3] tests/test_schema.py::test_constraints_schema_validation[kwargs21-Decimal-value21] tests/test_schema.py::test_constraints_schema_validation[kwargs22-Decimal-value22] tests/test_schema.py::test_constraints_schema_validation[kwargs23-Decimal-value23] tests/test_schema.py::test_constraints_schema_validation[kwargs24-Decimal-value24] tests/test_schema.py::test_constraints_schema_validation[kwargs25-Decimal-value25] tests/test_schema.py::test_constraints_schema_validation[kwargs26-Decimal-value26] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs0-str-foobar] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs1-str-f] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs2-str-bar] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs3-int-2] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs4-int-5] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs5-int-1] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs6-int-6] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs7-float-2.0] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs8-float-5.0] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs9-float-1.9] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs10-float-5.1] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs11-Decimal-value11] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs12-Decimal-value12] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs13-Decimal-value13] tests/test_schema.py::test_constraints_schema_validation_raises[kwargs14-Decimal-value14] tests/test_schema.py::test_schema_kwargs tests/test_schema.py::test_schema_dict_constr tests/test_schema.py::test_bytes_constrained_types[ConstrainedBytes-expected_schema0] tests/test_schema.py::test_bytes_constrained_types[ConstrainedBytesValue-expected_schema1] tests/test_schema.py::test_optional_dict tests/test_schema.py::test_optional_validator tests/test_schema.py::test_field_with_validator tests/test_schema.py::test_unparameterized_schema_generation tests/test_schema.py::test_known_model_optimization tests/test_schema.py::test_root tests/test_schema.py::test_root_list tests/test_schema.py::test_root_nested_model tests/test_schema.py::test_new_type_schema tests/test_schema.py::test_literal_schema tests/test_schema.py::test_literal_enum tests/test_schema.py::test_color_type tests/test_schema.py::test_model_with_schema_extra tests/test_schema.py::test_model_with_schema_extra_callable tests/test_schema.py::test_model_with_schema_extra_callable_no_model_class tests/test_schema.py::test_model_with_schema_extra_callable_classmethod tests/test_schema.py::test_model_with_schema_extra_callable_instance_method tests/test_schema.py::test_model_with_extra_forbidden tests/test_schema.py::test_enforced_constraints[int-kwargs0-field_schema0] tests/test_schema.py::test_enforced_constraints[annotation1-kwargs1-field_schema1] tests/test_schema.py::test_enforced_constraints[annotation2-kwargs2-field_schema2] tests/test_schema.py::test_enforced_constraints[annotation3-kwargs3-field_schema3] tests/test_schema.py::test_enforced_constraints[annotation4-kwargs4-field_schema4] tests/test_schema.py::test_enforced_constraints[annotation5-kwargs5-field_schema5] tests/test_schema.py::test_enforced_constraints[annotation6-kwargs6-field_schema6] tests/test_schema.py::test_enforced_constraints[annotation7-kwargs7-field_schema7] tests/test_schema.py::test_real_vs_phony_constraints tests/test_schema.py::test_subfield_field_info tests/test_schema.py::test_dataclass tests/test_schema.py::test_schema_attributes tests/test_schema.py::test_model_process_schema_enum tests/test_schema.py::test_path_modify_schema tests/test_schema.py::test_frozen_set tests/test_schema.py::test_iterable tests/test_schema.py::test_new_type tests/test_schema.py::test_multiple_models_with_same_name tests/test_schema.py::test_multiple_enums_with_same_name tests/test_schema.py::test_schema_for_generic_field tests/test_schema.py::test_namedtuple_default tests/test_schema.py::test_advanced_generic_schema tests/test_schema.py::test_nested_generic tests/test_schema.py::test_nested_generic_model tests/test_schema.py::test_complex_nested_generic tests/test_schema.py::test_schema_with_field_parameter tests/test_schema.py::test_discriminated_union tests/test_schema.py::test_discriminated_annotated_union tests/test_schema.py::test_alias_same