CODEWITHSUNDEEP
pythonsqlalchemy
zorro
zorro

Reputation: 75

Deleting non existing record should raise an error in sqlalchemy

Why deleting non-existing record does not raise an error in sqlalchemy. no feedback on whether the record was deleted or not.

session.query(Element).filter(Element.id==ElementId).delete()

Thank you for your clarification.

Upvotes: 7

Views: 9931

Answers (3)

Harshit
Harshit

Reputation: 1565

Adding an answer to @madogan, the edit queue was full and hence writing a new answer.

I've expanded his answer more in detail in a working solution:

class NoEntryFoundException(Exception):
    pass


def delete_row_entry(element_id: int):
    effected_rows = session.query(Element).filter(Element.id == element_id).delete()

    if effected_rows == 0:
        raise NoEntryFoundException(f'No row entry found with id: {element_id}')
    else:
        session.commit()

Upvotes: 0

madogan
madogan

Reputation: 665

Actually, sqlalchemy delete operation returns number of affected rows. So you can check and if affected rows is 0 then you can raise error.

effected_rows = session.query(Element).filter(Element.id==ElementId).delete()
if effected_rows == 0:
    # raise exception
else:
    # delete element

This works for me.

Upvotes: 4

dm03514
dm03514

Reputation: 55972

I don't think it is an error. For example it is perfectly legal to issue a query to delete records in sql that "don't exist"

If i have a table 'posts' with a column 'id'. with no records

DELETE FROM posts WHERE ID > 0;

It is perfectly valid sql, there is no error, even though there are no rows

I am not too familiar with sqlalchmey but could you check to see if value exists first?

element = session.query(Element).filter(Element.id==ElementId).first()
if element:
   # delete element
else:
   # raise exception

The above will issue an additional query though...

Also, if you want a delete method that raises error you can create your own session class Change SQLAlchemy's Session.delete() behaviour and override delete

As zzzeek points out delete with a criteria

Returns the number of rows deleted, excluding any cascades.

Which is another option for seeing if any rows are deleted

Upvotes: 8

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