Calling __init__ when parsing nested models

[dmontagu]

In pydantic v1:

from pydantic import BaseModel

class B(BaseModel):
    y: int

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        print('inner')


class A(BaseModel):
    x: B

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        print('outer')


A.parse_obj({'x': {'y': 2}})

This results in:

inner
outer

This doesn't currently work with the way validation happens in v2.

(@samuelcolvin you wanted me to create an issue about this — feel free to add color.)

[samuelcolvin]

problem is that V2 does

let instance = (*raw_type).tp_new ...;
force_setattr(py, instance, intern!(py, "__dict__"), model_dict)?;
...
force_setattr(py, instance, intern!(py, "__fields_set__"), fields_set)?;

Thereby, __init__ is never called

see

pydantic-core/src/validators/model.rs

Lines 133 to 152 in d7ff64d

	let raw_type = self.class.as_ref(py).as_type_ptr();
	let instance = unsafe {
	// Safety: raw_type is known to be a non-null type object pointer
	match (*raw_type).tp_new {
	// Safety: the result of new_func is guaranteed to be either an owned pointer or null on error returns.
	Some(new_func) => PyObject::from_owned_ptr_or_err(
	py,
	// Safety: the non-null pointers are known to be valid, and it's allowed to call tp_new with a
	// null kwargs dict.
	new_func(raw_type, args.as_ptr(), null_mut()),
	)?,
	None => return py_err!(PyTypeError; "base type without tp_new"),
	}
	};
	let instance_ref = instance.as_ref(py);
	force_setattr(py, instance_ref, intern!(py, "__dict__"), model_dict)?;
	if let Some(fields_set) = fields_set {
	force_setattr(py, instance_ref, intern!(py, "__fields_set__"), fields_set)?;
	}

[dmontagu]

Solution: we'll tell people to use a mode='wrap' root_validator to handle this logic.

• Need to confirm that you can override and call super().my_root_validator() and have it work the same as __init__ would
• Need to add this to the migration guide

[samuelcolvin]

This was fixed.