Anotasi yang Ditunda
Anotasi yang ditunda (seperti yang dijelaskan dalam PEP563 ) "berfungsi".
from __future__ import annotations
from typing import Any
from pydantic import BaseModel
class Model(BaseModel):
a: list[int]
b: Any
print(Model(a=('1', 2, 3), b='ok'))
#> a=[1, 2, 3] b='ok'
Secara internal, Pydantic akan memanggil metode yang mirip dengan typing.get_type_hints untuk menyelesaikan anotasi.
Bahkan tanpa menggunakan from __future__ import annotations , jika tipe yang direferensikan belum ditentukan, ForwardRef atau string dapat digunakan:
from typing import ForwardRef
from pydantic import BaseModel
Foo = ForwardRef('Foo')
class Foo(BaseModel):
a: int = 123
b: Foo = None
print(Foo())
#> a=123 b=None
print(Foo(b={'a': '321'}))
#> a=123 b=Foo(a=321, b=None)
Model Referensi Diri (atau "Rekursif").¶
Model dengan kolom referensi mandiri juga didukung. Bidang referensi mandiri akan diselesaikan secara otomatis setelah pembuatan model.
Di dalam model, Anda dapat merujuk ke model yang belum dibangun menggunakan string:
from pydantic import BaseModel
class Foo(BaseModel):
a: int = 123
#: The sibling of `Foo` is referenced by string
sibling: 'Foo' = None
print(Foo())
#> a=123 sibling=None
print(Foo(sibling={'a': '321'}))
#> a=123 sibling=Foo(a=321, sibling=None)
Jika Anda menggunakan from __future__ import annotations , Anda juga bisa merujuk ke model berdasarkan nama tipenya:
from __future__ import annotations
from pydantic import BaseModel
class Foo(BaseModel):
a: int = 123
#: The sibling of `Foo` is referenced directly by type
sibling: Foo = None
print(Foo())
#> a=123 sibling=None
print(Foo(sibling={'a': '321'}))
#> a=123 sibling=Foo(a=321, sibling=None)
Referensi siklik¶
Saat bekerja dengan model rekursif referensi mandiri, Anda mungkin menemukan referensi siklik dalam input validasi. Misalnya, hal ini dapat terjadi saat memvalidasi instance ORM dengan referensi balik dari atribut.
Daripada memunculkan Python RecursionError saat mencoba memvalidasi data dengan referensi siklik, Pydantic mampu mendeteksi referensi siklik dan memunculkan ValidationError yang sesuai :
from typing import Optional
from pydantic import BaseModel, ValidationError
class ModelA(BaseModel):
b: 'Optional[ModelB]' = None
class ModelB(BaseModel):
a: Optional[ModelA] = None
cyclic_data = {}
cyclic_data['a'] = {'b': cyclic_data}
print(cyclic_data)
#> {'a': {'b': {...}}}
try:
ModelB.model_validate(cyclic_data)
except ValidationError as exc:
print(exc)
"""
1 validation error for ModelB
a.b
Recursion error - cyclic reference detected [type=recursion_loop, input_value={'a': {'b': {...}}}, input_type=dict]
"""
Karena kesalahan ini muncul tanpa melebihi kedalaman rekursi maksimum, Anda dapat menangkap dan menangani ValidationError yang muncul tanpa perlu khawatir tentang kedalaman rekursi yang tersisa terbatas:
from contextlib import contextmanager
from dataclasses import field
from typing import Iterator, List
from pydantic import BaseModel, ValidationError, field_validator
def is_recursion_validation_error(exc: ValidationError) -> bool:
errors = exc.errors()
return len(errors) == 1 and errors[0]['type'] == 'recursion_loop'
@contextmanager
def suppress_recursion_validation_error() -> Iterator[None]:
try:
yield
except ValidationError as exc:
if not is_recursion_validation_error(exc):
raise exc
class Node(BaseModel):
id: int
children: List['Node'] = field(default_factory=list)
@field_validator('children', mode='wrap')
@classmethod
def drop_cyclic_references(cls, children, h):
try:
return h(children)
except ValidationError as exc:
if not (
is_recursion_validation_error(exc)
and isinstance(children, list)
):
raise exc
value_without_cyclic_refs = []
for child in children:
with suppress_recursion_validation_error():
value_without_cyclic_refs.extend(h([child]))
return h(value_without_cyclic_refs)
# Create data with cyclic references representing the graph 1 -> 2 -> 3 -> 1
node_data = {'id': 1, 'children': [{'id': 2, 'children': [{'id': 3}]}]}
node_data['children'][0]['children'][0]['children'] = [node_data]
print(Node.model_validate(node_data))
#> id=1 children=[Node(id=2, children=[Node(id=3, children=[])])]
Demikian pula, jika Pydantic menemukan referensi rekursif selama serialisasi , daripada menunggu hingga kedalaman rekursi maksimum terlampaui, ValueError akan segera dimunculkan:
from pydantic import TypeAdapter
# Create data with cyclic references representing the graph 1 -> 2 -> 3 -> 1
node_data = {'id': 1, 'children': [{'id': 2, 'children': [{'id': 3}]}]}
node_data['children'][0]['children'][0]['children'] = [node_data]
try:
# Try serializing the circular reference as JSON
TypeAdapter(dict).dump_json(node_data)
except ValueError as exc:
print(exc)
"""
Error serializing to JSON: ValueError: Circular reference detected (id repeated)
"""
Ini juga dapat ditangani jika diinginkan:
from dataclasses import field
from typing import Any, List
from pydantic import (
SerializerFunctionWrapHandler,
TypeAdapter,
field_serializer,
)
from pydantic.dataclasses import dataclass
@dataclass
class NodeReference:
id: int
@dataclass
class Node(NodeReference):
children: List['Node'] = field(default_factory=list)
@field_serializer('children', mode='wrap')
def serialize(
self, children: List['Node'], handler: SerializerFunctionWrapHandler
) -> Any:
"""
Serialize a list of nodes, handling circular references by excluding the children.
"""
try:
return handler(children)
except ValueError as exc:
if not str(exc).startswith('Circular reference'):
raise exc
result = []
for node in children:
try:
serialized = handler([node])
except ValueError as exc:
if not str(exc).startswith('Circular reference'):
raise exc
result.append({'id': node.id})
else:
result.append(serialized)
return result
# Create a cyclic graph:
nodes = [Node(id=1), Node(id=2), Node(id=3)]
nodes[0].children.append(nodes[1])
nodes[1].children.append(nodes[2])
nodes[2].children.append(nodes[0])
print(nodes[0])
#> Node(id=1, children=[Node(id=2, children=[Node(id=3, children=[...])])])
# Serialize the cyclic graph:
print(TypeAdapter(Node).dump_python(nodes[0]))
"""
{
'id': 1,
'children': [{'id': 2, 'children': [{'id': 3, 'children': [{'id': 1}]}]}],
}
"""
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