ForeignKeyColumn Class

This class is utilized when informing dataloom that a column has a relationship with a primary key in another table. Consider the following model definition of a Post

class Post(Model):
    __tablename__: Optional[TableColumn] = TableColumn(name="posts")
    id = PrimaryKeyColumn(type="int", auto_increment=True, nullable=False, unique=True)
    completed = Column(type="boolean", default=False)
    title = Column(type="varchar", length=255, nullable=False)
    # timestamps
    createdAt = CreatedAtColumn()
    updatedAt = UpdatedAtColumn()
    # relations
    userId = ForeignKeyColumn(
        User, type="int", required=True, onDelete="CASCADE", onUpdate="CASCADE"
    )

• userId is a foreign key in the table posts, indicating it has a relationship with a primary key in the users table.

This column accepts the following arguments

Argument	Description	Type	Default
table	Required. This is the parent table that the current model references. In our example, this is referred to as 'User'.	str	–
type	Optional. Specifies the data type of the foreign key. If not provided, dataloom can infer it from the parent table.	None	None
required	Optional. Indicates whether the foreign key is required or not.	bool	False
onDelete	Optional. Specifies the action to be taken when the associated record in the parent table is deleted.	"NO ACTION", "SET NULL", "CASCADE"	"NO ACTION"
onUpdate	Optional. Specifies the action to be taken when the associated record in the parent table is updated.	"NO ACTION", "SET NULL", "CASCADE"	"NO ACTION"

Tip

It is crucial to specify the actions for onDelete and onUpdate to ensure that dataloom manages your model’s relationship actions appropriately. The available actions are

1. "NO ACTION" - If you delete or update the parent table, no changes will occur in the child table.

2. "SET NULL" - If you delete or update the parent table, the corresponding value in the child table will be set to null.

3. "CASCADE" - If you delete or update the table, the same action will also be applied to the child table.