One to OneΒΆ

A one to one relationship associates one child with one parent and vice-versa. For example, the pay information for an employee may be stored in a different table than the employee. However, one employee can only be paid in one way and each employee must be paid separately.

See also

One to One

OpenAlchemy documentation for one to one relationships.

SQLAlchemy One to One

SQLAlchemy documentation for one to one relationships.

The following example defines a one to one relationship between Employee and PayInfo:

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openapi: "3.0.0"

info:
  title: Test Schema
  description: API to illustrate OpenAlchemy one to one relationship.
  version: "0.1"

paths:
  /pay_info:
    get:
      summary: Used to retrieve all payment information.
      responses:
        200:
          description: Return all payment information from the database.
          content:
            application/json:
              schema:
                type: array
                items:
                  "$ref": "#/components/schemas/PayInfo"
  /employee:
    get:
      summary: Used to retrieve all employees.
      responses:
        200:
          description: Return all employees from the database.
          content:
            application/json:
              schema:
                type: array
                items:
                  "$ref": "#/components/schemas/Employee"

components:
  schemas:
    PayInfo:
      description: Information on how to pay an employee.
      type: object
      x-tablename: pay_info
      properties:
        id:
          type: integer
          description: Unique identifier for the pay information.
          example: 0
          x-primary-key: true
        account_number:
          type: string
          description: The account number to pay the employee into.
          example: David's Account
    Employee:
      description: Person that works for a company.
      type: object
      x-tablename: employee
      properties:
        id:
          type: integer
          description: Unique identifier for the employee.
          example: 0
          x-primary-key: true
        name:
          type: string
          description: The name of the employee.
          example: David Andersson
        pay_info:
          allOf:
            - "$ref": "#/components/schemas/PayInfo"
            - x-backref: employee
              x-uselist: false

The following file uses OpenAlchemy to generate the SQLAlchemy models:

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from open_alchemy import init_yaml

init_yaml("example-spec.yml", models_filename="models_auto.py")

The SQLAlchemy models generated by OpenAlchemy are equivalent to the following traditional models file:

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import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class PayInfo(Base):
    """Information on how to pay an employee."""

    __tablename__ = "pay_info"
    id = sa.Column(sa.Integer, primary_key=True)
    account_number = sa.Column(sa.String)


class Employee(Base):
    """Person that works for a company."""

    __tablename__ = "employee"
    id = sa.Column(sa.Integer, primary_key=True)
    name = sa.Column(sa.String)
    pay_info_id = sa.Column(sa.Integer, sa.ForeignKey("pay_info.id"))
    pay_info = sa.orm.relationship("PayInfo", uselist=False)

OpenAlchemy will generate the following typed models:

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"""Autogenerated SQLAlchemy models based on OpenAlchemy models."""
# pylint: disable=no-member,super-init-not-called,unused-argument

import typing

import sqlalchemy
from sqlalchemy import orm

from open_alchemy import models

Base = models.Base  # type: ignore


class PayInfoDict(typing.TypedDict, total=False):
    """TypedDict for properties that are not required."""

    id: typing.Optional[int]
    account_number: typing.Optional[str]


class TPayInfo(typing.Protocol):
    """
    SQLAlchemy model protocol.

    Information on how to pay an employee.

    Attrs:
        id: Unique identifier for the pay information.
        account_number: The account number to pay the employee into.
        employee: The employee of the PayInfo.

    """

    # SQLAlchemy properties
    __table__: sqlalchemy.Table
    __tablename__: str
    query: orm.Query

    # Model properties
    id: "sqlalchemy.Column[typing.Optional[int]]"
    account_number: "sqlalchemy.Column[typing.Optional[str]]"
    employee: 'sqlalchemy.Column[typing.Optional["TEmployee"]]'

    def __init__(
        self,
        id: typing.Optional[int] = None,
        account_number: typing.Optional[str] = None,
        employee: typing.Optional["TEmployee"] = None,
    ) -> None:
        """
        Construct.

        Args:
            id: Unique identifier for the pay information.
            account_number: The account number to pay the employee into.
            employee: The employee of the PayInfo.

        """
        ...

    @classmethod
    def from_dict(
        cls,
        id: typing.Optional[int] = None,
        account_number: typing.Optional[str] = None,
    ) -> "TPayInfo":
        """
        Construct from a dictionary (eg. a POST payload).

        Args:
            id: Unique identifier for the pay information.
            account_number: The account number to pay the employee into.
            employee: The employee of the PayInfo.

        Returns:
            Model instance based on the dictionary.

        """
        ...

    @classmethod
    def from_str(cls, value: str) -> "TPayInfo":
        """
        Construct from a JSON string (eg. a POST payload).

        Returns:
            Model instance based on the JSON string.

        """
        ...

    def to_dict(self) -> PayInfoDict:
        """
        Convert to a dictionary (eg. to send back for a GET request).

        Returns:
            Dictionary based on the model instance.

        """
        ...

    def to_str(self) -> str:
        """
        Convert to a JSON string (eg. to send back for a GET request).

        Returns:
            JSON string based on the model instance.

        """
        ...


PayInfo: typing.Type[TPayInfo] = models.PayInfo  # type: ignore


class EmployeeDict(typing.TypedDict, total=False):
    """TypedDict for properties that are not required."""

    id: typing.Optional[int]
    name: typing.Optional[str]
    pay_info: typing.Optional["PayInfoDict"]


class TEmployee(typing.Protocol):
    """
    SQLAlchemy model protocol.

    Person that works for a company.

    Attrs:
        id: Unique identifier for the employee.
        name: The name of the employee.
        pay_info: The pay_info of the Employee.

    """

    # SQLAlchemy properties
    __table__: sqlalchemy.Table
    __tablename__: str
    query: orm.Query

    # Model properties
    id: "sqlalchemy.Column[typing.Optional[int]]"
    name: "sqlalchemy.Column[typing.Optional[str]]"
    pay_info: 'sqlalchemy.Column[typing.Optional["TPayInfo"]]'

    def __init__(
        self,
        id: typing.Optional[int] = None,
        name: typing.Optional[str] = None,
        pay_info: typing.Optional["TPayInfo"] = None,
    ) -> None:
        """
        Construct.

        Args:
            id: Unique identifier for the employee.
            name: The name of the employee.
            pay_info: The pay_info of the Employee.

        """
        ...

    @classmethod
    def from_dict(
        cls,
        id: typing.Optional[int] = None,
        name: typing.Optional[str] = None,
        pay_info: typing.Optional["PayInfoDict"] = None,
    ) -> "TEmployee":
        """
        Construct from a dictionary (eg. a POST payload).

        Args:
            id: Unique identifier for the employee.
            name: The name of the employee.
            pay_info: The pay_info of the Employee.

        Returns:
            Model instance based on the dictionary.

        """
        ...

    @classmethod
    def from_str(cls, value: str) -> "TEmployee":
        """
        Construct from a JSON string (eg. a POST payload).

        Returns:
            Model instance based on the JSON string.

        """
        ...

    def to_dict(self) -> EmployeeDict:
        """
        Convert to a dictionary (eg. to send back for a GET request).

        Returns:
            Dictionary based on the model instance.

        """
        ...

    def to_str(self) -> str:
        """
        Convert to a JSON string (eg. to send back for a GET request).

        Returns:
            JSON string based on the model instance.

        """
        ...


Employee: typing.Type[TEmployee] = models.Employee  # type: ignore