python data_error ai_generated true

pydantic_core._pydantic_core.ValidationError: 1 validation error for RootModel[list[Item]] Input should be a valid list [type=list_type, input_value={'a': 1}, input_type=dict]

ID: python/pydantic-rootmodel-list

Also available as: JSON · Markdown · 中文
80%Fix Rate
88%Confidence
0Evidence
2024-02-14First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
2.x active — — —

Root Cause

A RootModel[list[...]] received a dict. In v2, RootModel wraps the root value directly, so the input must be the list itself, not {'root': [...]}.

generic

中文

RootModel[list[...]] 接收到了一个 dict。在 v2 中 RootModel 直接包装根值，因此输入必须是列表本身，而不是 {'root': [...]}。

Workarounds

  1. 95% success 
    from pydantic import RootModel
Items = RootModel[list[Item]]
Items.model_validate([{'a': 1}])
  2. 90% success 
    from pydantic import TypeAdapter
ta = TypeAdapter(list[Item])
ta.validate_python([{'a': 1}])

Dead Ends

Common approaches that don't work:

  1. 70% fail

    v2 removed the implicit 'root' key; the model now expects the bare value.

  2. 75% fail

    __root__ is a v1 feature and raises PydanticUserError under v2.

  3. 50% fail

    Loses Pydantic validation and serialization hooks.