diff options
Diffstat (limited to 'lib/sqlalchemy/orm/query.py')
| -rw-r--r-- | lib/sqlalchemy/orm/query.py | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py index 592c685ca..f74fd44bb 100644 --- a/lib/sqlalchemy/orm/query.py +++ b/lib/sqlalchemy/orm/query.py @@ -3073,6 +3073,32 @@ class Query(object): .. warning:: **Additional Caveats for bulk query deletes** + * This method does **not work for joined + inheritance mappings**, since the **multiple table + deletes are not supported by SQL** as well as that the + **join condition of an inheritance mapper is not + automatically rendered**. Care must be taken in any + multiple-table delete to first accomodate via some other means + how the related table will be deleted, as well as to + explicitly include the joining + condition between those tables, even in mappings where + this is normally automatic. E.g. if a class ``Engineer`` + subclasses ``Employee``, a DELETE against the ``Employee`` + table would look like:: + + session.query(Engineer).\\ + filter(Engineer.id == Employee.id).\\ + filter(Employee.name == 'dilbert').\\ + delete() + + However the above SQL will not delete from the Engineer table, + unless an ON DELETE CASCADE rule is established in the database + to handle it. + + Short story, **do not use this method for joined inheritance + mappings unless you have taken the additional steps to make + this feasible**. + * The method does **not** offer in-Python cascading of relationships - it is assumed that ON DELETE CASCADE/SET NULL/etc. is configured for any foreign key references |