model_validate ignores relationship lists

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• I already checked if it is not related to SQLModel but to SQLAlchemy.

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Example Code

from pydantic import BaseModel
from sqlmodel import SQLModel, Relationship, Field

if __name__ == "__main__":

    # Sqlmodel classes
    class SqlChild(SQLModel, table=True):
        id: int = Field(primary_key=True, default=None)
        number: int
        parent_id: int = Field(foreign_key="sqlparent.id")

    class SqlParent(SQLModel, table=True):
        id: int = Field(primary_key=True, default=None)
        name: str
        children: list[SqlChild] = Relationship()

    # Regular pydantic classes
    class PydanticChild(BaseModel):
        id: int = Field(primary_key=True, default=None)
        number: int

    class PydanticParent(SQLModel):
        id: int = Field(primary_key=True, default=None)
        name: str
        children: list[PydanticChild]

    # Pydantic classes work as expected
    print(PydanticParent.model_validate({"name": "Hello", "children": [{"number": 4}]})) # -> id=None name='Hello' children=[PydanticChild(id=None, number=4)]
    print(PydanticParent.model_validate({"name": "Hello", "children": [PydanticChild(number=4)]})) # -> id=None name='Hello' children=[PydanticChild(id=None, number=4)]

    # Sqlmodel classes does not
    print(SqlParent.model_validate({"name": "Hello", "children": [{"number": 4}]})) # -> id=None name='Hello'
    print(SqlParent.model_validate({"name": "Hello", "children": [SqlChild(number=4)]})) # -> id=None name='Hello'

Description

Pydantic unpacks lists passed to model_validate but sqlmodel does not. If the library claims to be compatible with pydantic I'm not sure if this behaviour is correct or not

Operating System

Linux

Operating System Details

No response

SQLModel Version

0.0.24

Python Version

3.13.2

Additional Context

May be related to #1092

[Muguett-DBY]

Relationship() attributes are SQLAlchemy relationships, not Pydantic fields. For example, "children" not in SqlParent.model_fields. With dictionary input, SqlParent.model_validate() does not turn the nested values into related ORM instances; both dictionary examples still produce an empty relationship on 0.0.48.

For nested request data, validate a non-table input model first, then construct the related table objects explicitly. Using your SqlParent and SqlChild:

class ChildInput(SQLModel):
    number: int


class ParentInput(SQLModel):
    name: str
    children: list[ChildInput]


data = ParentInput.model_validate(
    {"name": "Hello", "children": [{"number": "4"}]}
)
parent = SqlParent.model_validate(data.model_dump(exclude={"children"}))
parent.children = [SqlChild(number=child.number) for child in data.children]

assert parent.children[0].number == 4

with Session(engine) as session:
    session.add(parent)
    session.commit()

Here Session comes from sqlmodel, and engine has your tables created. The relationship saves the children and fills parent_id when the parent is inserted; you don't need the generated parent ID beforehand. This follows the relationship assignment pattern in the tutorial.

Also, printing the parent is not a reliable check: its repr omits relationships even when parent.children is populated.

Checked with Codex assistance on SQLModel 0.0.24/Pydantic 2.11.7 and SQLModel 0.0.48/Pydantic 2.14.1. On both, I committed and reloaded the graph in a new SQLite session and checked the child foreign keys. Invalid nested numbers raise validation errors before any ORM objects are created.