# example.json
{
    "multiplier": 5,
    "field_1": {
        "value": 1
    },
    "field_2": {
        "value": 2
    }
}

# example.py
from pydantic import BaseModel, validator
class Item(BaseModel):
    value: int
class Container(BaseModel):
    multiplier: int
    field_1: Item
    field_2: Item

class Item(BaseModel):
    value: int
    @validator("value")
    @classmethod
    def validate_value(cls, value):
        return value # * multiplier  # <--- can I get access to Container's multiplier here?

from pydantic import BaseModel, validator
class Item(BaseModel):
    value: int
class Container(BaseModel):
    multiplier: int
    field_1: Item
    field_2: Item
    @validator("field_1", "field_2")
    def validate_value(cls, v, values):
        """Validate each item"""
        m = values["multiplier"]

class Item(BaseModel):
    value: int
    @classmethod
    def validate_value(cls, v, **kwargs):
        """Validate each item"""
        m = kwargs.get("multiplier")
        if m * v.value < 10:
            raise ValueError
        return v
class Container(BaseModel):
    multiplier: int
    field_1: Item
    field_2: Item
    @validator("field_1", "field_2", pre=False)
    def validate_items(cls, v, values):
        return Item.validate_value(v, **values)

from pydantic import BaseModel, Field, validator
class Item(BaseModel):
    multiplier: int  # exclude from parent serialization, workaround for validation
    value: int
    @validator("value", pre=False)
    def validate_value(cls, v, values):
        """Validate each item"""
        m = values["multiplier"]
        if m * v < 10:
            raise ValueError
        return v
class Container(BaseModel):
    multiplier: int
    field_1: Item = Field(..., exclude={'multiplier'})
    field_2: Item = Field(..., exclude={'multiplier'})
    @validator("field_1", "field_2", pre=True)
    def validate_items(cls, v, values):
        
        # Construct from a value, another workaround
        if isinstance(v, int):
            return Item(value=v, multiplier=values["multiplier"])
        
        elif isinstance(v, Item):
            return Item(value=v.value, multiplier=values["multiplier"])
if __name__ == '__main__':
    c = Container(
        multiplier=1,
        field_1=11,
        field_2=22
    )

from pydantic import BaseModel, field_validator, model_validator
from contextvars import ContextVar
context_multiplier = ContextVar("context_multiplier")
class Item(BaseModel):
    value: int
    @field_validator("value")
    @classmethod
    def validate_value(cls, value):
        multiplier = context_multiplier.get()
        if value % multiplier != 0:
            raise ValueError(f"not a multiple of {multiplier}")
        return value
class Container(BaseModel):
    multiplier: int
    field_1: Item
    field_2: Item
    @model_validator(mode="wrap")
    @classmethod
    def validate_model(cls, v, handler):
        try:
            multiplier = int(v["multiplier"])
        except KeyError:
            raise ValueError("multiplier required")
        token = context_multiplier.set(v["multiplier"])
        try:
            return handler(v)
        finally:
            context_multiplier.reset(token)

>>> Container.model_validate(
...     {"multiplier": 3, "field_1": {"value": 9}, "field_2": {"value": 12}}
... )
Container(multiplier=3, field_1=Item(value=9), field_2=Item(value=12))

>>> Container.model_validate(
...     {"multiplier": 3, "field_1": {"value": 9}, "field_2": {"value": 11}}
... )
pydantic_core._pydantic_core.ValidationError: 1 validation error for Container
field_2.value
  Value error, not a multiple of 3 [type=value_error, input_value=11, input_type=int]
    For further information visit https://errors.pydantic.dev/2.1.2/v/value_error