Many to Many¶
The many to many relationship is used when a parent model can have many children but the child can also have many parents. For example, an employee could be working on multiple projects and multiple employees are generally assigned to a project.
See also
- Many to Many
OpenAlchemy documentation for many to many relationships.
- SQLAlchemy Many to Many
SQLAlchemy documentation for many to many relationships.
The following example defines a many to many relationship between
Employee
and Project
:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | openapi: "3.0.0" info: title: Test Schema description: API to illustrate Many to Many Relationships. version: "0.1" paths: /project: get: summary: Used to retrieve all projects. responses: 200: description: Return all projects from the database. content: application/json: schema: type: array items: "$ref": "#/components/schemas/Project" /employee: get: summary: Used to retrieve all employees. responses: 200: description: Return all employees from the database. content: application/json: schema: type: array items: "$ref": "#/components/schemas/Employee" components: schemas: Project: description: A large sized business objective. type: object x-tablename: project properties: id: type: integer description: Unique identifier for the project. example: 0 x-primary-key: true name: type: string description: The name of the project. example: Expand to the USA 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 projects: type: array items: allOf: - "$ref": "#/components/schemas/Project" - x-secondary: employee_project description: The projects the employee is working on. |
The following file uses OpenAlchemy to generate the SQLAlchemy models:
1 2 3 | 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | import sqlalchemy as sa from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() employee_project = sa.Table( "employee_project", Base.metadata, sa.Column("project_id", sa.Integer, sa.ForeignKey("project.id")), sa.Column("employee_id", sa.Integer, sa.ForeignKey("employee.id")), ) class Project(Base): """A large sized business objective.""" __tablename__ = "project" id = sa.Column(sa.Integer, primary_key=True) name = 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) projects = sa.orm.relationship("Project", secondary="project_employee") |
OpenAlchemy will generate the following typed models:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 | """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 ProjectDict(typing.TypedDict, total=False): """TypedDict for properties that are not required.""" id: typing.Optional[int] name: typing.Optional[str] class TProject(typing.Protocol): """ SQLAlchemy model protocol. A large sized business objective. Attrs: id: Unique identifier for the project. name: The name of the project. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties id: "sqlalchemy.Column[typing.Optional[int]]" name: "sqlalchemy.Column[typing.Optional[str]]" def __init__( self, id: typing.Optional[int] = None, name: typing.Optional[str] = None ) -> None: """ Construct. Args: id: Unique identifier for the project. name: The name of the project. """ ... @classmethod def from_dict( cls, id: typing.Optional[int] = None, name: typing.Optional[str] = None ) -> "TProject": """ Construct from a dictionary (eg. a POST payload). Args: id: Unique identifier for the project. name: The name of the project. Returns: Model instance based on the dictionary. """ ... @classmethod def from_str(cls, value: str) -> "TProject": """ Construct from a JSON string (eg. a POST payload). Returns: Model instance based on the JSON string. """ ... def to_dict(self) -> ProjectDict: """ 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. """ ... Project: typing.Type[TProject] = models.Project # type: ignore class EmployeeDict(typing.TypedDict, total=False): """TypedDict for properties that are not required.""" id: typing.Optional[int] name: typing.Optional[str] projects: typing.Sequence["ProjectDict"] 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. projects: The projects the employee is working on. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties id: "sqlalchemy.Column[typing.Optional[int]]" name: "sqlalchemy.Column[typing.Optional[str]]" projects: 'sqlalchemy.Column[typing.Sequence["TProject"]]' def __init__( self, id: typing.Optional[int] = None, name: typing.Optional[str] = None, projects: typing.Optional[typing.Sequence["TProject"]] = None, ) -> None: """ Construct. Args: id: Unique identifier for the employee. name: The name of the employee. projects: The projects the employee is working on. """ ... @classmethod def from_dict( cls, id: typing.Optional[int] = None, name: typing.Optional[str] = None, projects: typing.Optional[typing.Sequence["ProjectDict"]] = None, ) -> "TEmployee": """ Construct from a dictionary (eg. a POST payload). Args: id: Unique identifier for the employee. name: The name of the employee. projects: The projects the employee is working on. 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 class EmployeeProjectDict(typing.TypedDict, total=True): """TypedDict for properties that are required.""" employee_id: int project_id: int class TEmployeeProject(typing.Protocol): """ SQLAlchemy model protocol. Attrs: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties employee_id: "sqlalchemy.Column[int]" project_id: "sqlalchemy.Column[int]" def __init__(self, employee_id: int, project_id: int) -> None: """ Construct. Args: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. """ ... @classmethod def from_dict(cls, employee_id: int, project_id: int) -> "TEmployeeProject": """ Construct from a dictionary (eg. a POST payload). Args: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. Returns: Model instance based on the dictionary. """ ... @classmethod def from_str(cls, value: str) -> "TEmployeeProject": """ Construct from a JSON string (eg. a POST payload). Returns: Model instance based on the JSON string. """ ... def to_dict(self) -> EmployeeProjectDict: """ 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. """ ... EmployeeProject: typing.Type[TEmployeeProject] = models.EmployeeProject # type: ignore |
Custom Association Schema¶
OpenAlchemy also supports customization of the association schema that implements the many-to-many relationship. This means that the schema can be changed to include, for example, a column tracking when the association was established.
See also
- Custom Association Schema
OpenAlchemy documentation for many to many relationships with a custom association schema.
The following example defines a schema for the association:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 | openapi: "3.0.0" info: title: Test Schema description: API to illustrate Many to Many Relationships. version: "0.1" paths: /project: get: summary: Used to retrieve all projects. responses: 200: description: Return all projects from the database. content: application/json: schema: type: array items: "$ref": "#/components/schemas/Project" /employee: get: summary: Used to retrieve all employees. responses: 200: description: Return all employees from the database. content: application/json: schema: type: array items: "$ref": "#/components/schemas/Employee" components: schemas: Project: description: A large sized business objective. type: object x-tablename: project properties: id: type: integer description: Unique identifier for the project. example: 0 x-primary-key: true name: type: string description: The name of the project. example: Expand to the USA Employee: description: Person that works for a company. type: object x-tablename: employee properties: id: type: integer description: Unique identifier for the employee. example: 0 x-primary-key: true name: type: string description: The name of the employee. example: David Andersson projects: type: array items: allOf: - "$ref": "#/components/schemas/Project" - x-secondary: employee_project description: The projects the employee is working on. EmployeeProject: type: object x-tablename: employee_project properties: employee_id: type: integer x-primary-key: true x-foreign-key: employee.id project_id: type: integer x-primary-key: true x-foreign-key: project.id required: - employee_id - project_id |
The following file uses OpenAlchemy to generate the SQLAlchemy models:
1 2 3 | from open_alchemy import init_yaml init_yaml("pre-defined-example-spec.yml", models_filename="pre_defined_models_auto.py") |
The SQLAlchemy models generated by OpenAlchemy are equivalent to the following traditional models file:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | import sqlalchemy as sa from sqlalchemy.ext.declarative import declarative_base Base = declarative_base() class Project(Base): """A large sized business objective.""" __tablename__ = "project" id = sa.Column(sa.Integer, primary_key=True) name = 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) projects = sa.orm.relationship("Project", secondary="project_employee") class EmployeeProject(Base): """Person that works for a company.""" __tablename__ = "project_employee" employee_id = sa.Column(sa.Integer, sa.ForeignKey("employee.id"), primary_key=True) employee_id = sa.Column(sa.Integer, sa.ForeignKey("project.id"), primary_key=True) |
OpenAlchemy will generate the following typed models:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 | """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 ProjectDict(typing.TypedDict, total=False): """TypedDict for properties that are not required.""" id: typing.Optional[int] name: typing.Optional[str] class TProject(typing.Protocol): """ SQLAlchemy model protocol. A large sized business objective. Attrs: id: Unique identifier for the project. name: The name of the project. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties id: "sqlalchemy.Column[typing.Optional[int]]" name: "sqlalchemy.Column[typing.Optional[str]]" def __init__( self, id: typing.Optional[int] = None, name: typing.Optional[str] = None ) -> None: """ Construct. Args: id: Unique identifier for the project. name: The name of the project. """ ... @classmethod def from_dict( cls, id: typing.Optional[int] = None, name: typing.Optional[str] = None ) -> "TProject": """ Construct from a dictionary (eg. a POST payload). Args: id: Unique identifier for the project. name: The name of the project. Returns: Model instance based on the dictionary. """ ... @classmethod def from_str(cls, value: str) -> "TProject": """ Construct from a JSON string (eg. a POST payload). Returns: Model instance based on the JSON string. """ ... def to_dict(self) -> ProjectDict: """ 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. """ ... Project: typing.Type[TProject] = models.Project # type: ignore class EmployeeDict(typing.TypedDict, total=False): """TypedDict for properties that are not required.""" id: typing.Optional[int] name: typing.Optional[str] projects: typing.Sequence["ProjectDict"] 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. projects: The projects the employee is working on. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties id: "sqlalchemy.Column[typing.Optional[int]]" name: "sqlalchemy.Column[typing.Optional[str]]" projects: 'sqlalchemy.Column[typing.Sequence["TProject"]]' def __init__( self, id: typing.Optional[int] = None, name: typing.Optional[str] = None, projects: typing.Optional[typing.Sequence["TProject"]] = None, ) -> None: """ Construct. Args: id: Unique identifier for the employee. name: The name of the employee. projects: The projects the employee is working on. """ ... @classmethod def from_dict( cls, id: typing.Optional[int] = None, name: typing.Optional[str] = None, projects: typing.Optional[typing.Sequence["ProjectDict"]] = None, ) -> "TEmployee": """ Construct from a dictionary (eg. a POST payload). Args: id: Unique identifier for the employee. name: The name of the employee. projects: The projects the employee is working on. 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 class EmployeeProjectDict(typing.TypedDict, total=True): """TypedDict for properties that are required.""" employee_id: int project_id: int class TEmployeeProject(typing.Protocol): """ SQLAlchemy model protocol. Attrs: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. """ # SQLAlchemy properties __table__: sqlalchemy.Table __tablename__: str query: orm.Query # Model properties employee_id: "sqlalchemy.Column[int]" project_id: "sqlalchemy.Column[int]" def __init__(self, employee_id: int, project_id: int) -> None: """ Construct. Args: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. """ ... @classmethod def from_dict(cls, employee_id: int, project_id: int) -> "TEmployeeProject": """ Construct from a dictionary (eg. a POST payload). Args: employee_id: The employee_id of the EmployeeProject. project_id: The project_id of the EmployeeProject. Returns: Model instance based on the dictionary. """ ... @classmethod def from_str(cls, value: str) -> "TEmployeeProject": """ Construct from a JSON string (eg. a POST payload). Returns: Model instance based on the JSON string. """ ... def to_dict(self) -> EmployeeProjectDict: """ 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. """ ... EmployeeProject: typing.Type[TEmployeeProject] = models.EmployeeProject # type: ignore |