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ondelete cascade

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Manish Bhusal answered on July 13, 2020 Popularity 9/10 Helpfulness 2/10

answer ondelete cascade

related sqlmodel ondelete cascade

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related on_delete=models.cascade

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ondelete cascade

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When the referenced object is deleted, all objects that have 
a foreign key to it will also be deleted.

For example, let's say we have an Author named "John" and two 
books associated with him. If we delete the "John" Author object, 
the two Book objects associated with "John" will also be 
deleted automatically.

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

Popularity 9/10 Helpfulness 2/10 Language python

Source: Grepper

Tags: cascade python

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Contributed on May 18 2023

Manish Bhusal

0 Answers Avg Quality 2/10

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sqlmodel ondelete cascade

Comment

from typing import List, Optional
from sqlmodel import Field, Relationship, Session, SQLModel, create_engine


class Hero(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    tests: List["Test"] = Relationship(
        sa_relationship_kwargs={"cascade": "delete"}
        # Doesn't work vvv
        # sa_relationship_kwargs={"cascade": "all, delete"}
    )


class Test(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    hero_id: Optional[int] = Field(default=None, foreign_key="hero.id")


engine = create_engine("sqlite:///", echo=True)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


def create_heroes():
    hero = Hero(name="Deadpond", secret_name="Dive Wilson")
    t1 = Test()
    t2 = Test()
    hero.tests = [t1, t2]

    with Session(engine) as session:
        session.add(hero)
        session.commit()
        session.query(Hero).delete()
        session.commit()
        heroes = session.query(Hero).all()
        print(heroes)
        assert len(heroes) == 0
        tests = session.query(Test).all()
        print(tests)
        assert len(tests) == 0


def main():  #
    create_db_and_tables()  #
    create_heroes()  #


if __name__ == "__main__":  #
    main()

"""
2022-01-13 15:37:54,273 INFO sqlalchemy.engine.Engine DELETE FROM hero
2022-01-13 15:37:54,273 INFO sqlalchemy.engine.Engine [generated in 0.00006s] ()
2022-01-13 15:37:54,273 INFO sqlalchemy.engine.Engine COMMIT
2022-01-13 15:37:54,273 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2022-01-13 15:37:54,274 INFO sqlalchemy.engine.Engine SELECT hero.id AS hero_id 
FROM hero
2022-01-13 15:37:54,274 INFO sqlalchemy.engine.Engine [generated in 0.00006s] ()
[]
2022-01-13 15:37:54,275 INFO sqlalchemy.engine.Engine SELECT test.id AS test_id, test.hero_id AS test_hero_id 
FROM test
2022-01-13 15:37:54,275 INFO sqlalchemy.engine.Engine [generated in 0.00006s] ()
[]
2022-01-13 15:37:54,275 INFO sqlalchemy.engine.Engine ROLLBACK
"""

Popularity 8/10 Helpfulness 5/10 Language python

Source: Grepper

Tags: cascade python p

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Contributed on Sep 20 2023

serge kalaga

0 Answers Avg Quality 2/10

onDelete->cascade whats the mean?

Comment

The onDelete('cascade') means that when the row is deleted, 
it will delete all it's references and attached data too.

(Source: https://stackoverflow.com/questions/43094543/what-does-ondeletecascade-mean#:~:text=The%20onDelete('cascade'),references%20and%20attached%20data%20too.)

Popularity 9/10 Helpfulness 5/10 Language typescript

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Contributed on Jan 11 2023

Panicky Petrel

0 Answers Avg Quality 2/10

on_delete=models.cascade

Comment

on_delete=models.CASCADE will delete anything created by the admin if
the admin user is deleted.

Popularity 10/10 Helpfulness 4/10 Language python

Source: Grepper

Tags: python py

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Contributed on Jul 13 2020

Virgin Programmer

0 Answers Avg Quality 2/10

ON DELETE CASCADE

Comment

CREATE TBALE parent_table_p (
           id INT PRIMARY KEY
)
CREATE_TABLE child_table_c(
           id INT PRIMARY KEY,
           parent_id INT,
           FOREIGN KEY (parent_id) REFERENCES parent_table_p(id) ON DELETE CASCADE
)

Popularity 9/10 Helpfulness 3/10 Language sql

Source: Grepper

Tags: cascade

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Contributed on Feb 16 2024

abdul bari shaikh

0 Answers Avg Quality 2/10

on delete cascade

Comment

The ON DELETE CASCADE clause specifies that if a row in the
table A is deleted, any rows in the table B that reference the deleted 
row will also be deleted.

Popularity 10/10 Helpfulness 2/10 Language sql

Source: Grepper

Tags: cascade

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Contributed on Dec 24 2022

ekkamrit

0 Answers Avg Quality 2/10

on delete cascade

Comment

CREATE TABLE child_table
(
  column1 datatype [ NULL | NOT NULL ],
  column2 datatype [ NULL | NOT NULL ],
  ...

  CONSTRAINT fk_name
    FOREIGN KEY (child_col1, child_col2, ... child_col_n)
    REFERENCES parent_table (parent_col1, parent_col2, ... parent_col_n)
    ON DELETE CASCADE
    [ ON UPDATE { NO ACTION | CASCADE | SET NULL | SET DEFAULT } ] 
);

Popularity 10/10 Helpfulness 2/10 Language whatever

Source: www.techonthenet.com

Tags: cascade

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Contributed on Nov 11 2020

Grieving Grivet

0 Answers Avg Quality 2/10

on delete cascade

Comment

CREATE TABLE Enroll (
    sno INT,
    cno INT,
    jdate date,
    PRIMARY KEY(sno,cno),
    FOREIGN KEY(sno) 
        REFERENCES Student(sno)
        ON DELETE CASCADE
    FOREIGN KEY(cno) 
        REFERENCES Course(cno)
        ON DELETE CASCADE
);

Popularity 10/10 Helpfulness 2/10 Language sql

Source: www.geeksforgeeks.org

Tags: cascade

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Contributed on Sep 06 2022

Bored Buzzard

0 Answers Avg Quality 2/10

ondelete cascade

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onDelete->cascade whats the mean?

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ON DELETE CASCADE

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