FastAPI SQLModel not returning list of children in JSON even though they are present

Question

I have the following two models:

class TableRecord(SQLModel, table=True):  # Define parent after child
    __tablename__: str = "table_record"
    record_key: Optional[int] = Field(default=None, primary_key=True)
    table_id: int  # Assuming foreign_key="table.id" is defined elsewhere
    created_by: int # = Field(foreign_key="user.id")

    values: list["TableRecordValue"] = Relationship(back_populates="table_record")



class TableRecordValue(SQLModel, table=True):  # Define child first
    __tablename__: str = "table_record_value"
    id: Optional[int] = Field(default=None, primary_key=True)
    column_id: int  # Assuming foreign_key="table_column.id" is defined elsewhere
    value: str
    updated_on: Optional[datetime] = Field(default_factory=datetime.utcnow)
    updated_by: int  # Assuming foreign_key="user.id" is defined elsewhere

    record_key: Optional[int] = Field(foreign_key="table_record.record_key")
    table_record: "TableRecord" = Relationship(back_populates="values")

I have the following endpoint:

@table_records_router.get("/table_records/{record_key}", response_model=TableRecord)
def get_table_record(record_key: int):
    with Session(engine) as session:
        statement = select(TableRecord).where(TableRecord.record_key == record_key)
        table_record = session.exec(statement).first()
        if not table_record:
            raise HTTPException(status_code=404, detail=f"TableRecord with key {record_key} not found")

        print(table_record.values) # Data is present here
        return table_record # The returned data from the endpoint no longer includes the values (["values"] gives keyError)

Why are the values not present anymore in the returned json?