Similar to this question on insert.
I wonder how we do update for a many-to-many relation using flask-sqlalchemy?
Related
For a project i need to to delete all data from all tables in a database,
I tried
DELETE FROM table1,table2,table3,...;
But it doesnt work. Any advice ? Thank
I would like to refer You to this related post
How do I use cascade delete with SQL Server?
as You will find there several possible solutions.
When using SQL it means that Your data is relations, which means most of the records are somehow related in the different tables and this relation is expressed with foreign keys. However when attempting to delete data which is id is related with data in another table a cascade deletion should be implemented, the other way around it is add additional boolean column named isDeleted(as example ofcourse) and just alter specific rows to true in this specific column and then filter by preferences. Hopefully I have managed somehow to provide with alternative and/or possible solution to Your problem.
Leaving also this link which gives some examples on cascade deletion and guide on how to implement it. ->
https://www.sqlshack.com/delete-cascade-and-update-cascade-in-sql-server-foreign-key/
P.S. also if You want just to DELETE all the data You can either use TRUNCATE TABLE or DROP DATABASE query. With the latest option You will have to recreate the database once more.
Because you want to delete all databases from all tables, you are essentially deleting the database.
The sqlite way of doing this is to just delete the database file.
In contrast to postgres or mongodb or most databases, sqlite doesn't have a server so no need to call DROP DATABASE.
As soon as the file is gone and you open the database from your application you will be in a blank state again.
I am working with EF Core 6.0 and SQL Server. I have an Articles table (with associated temporal table named ArticlesHistory).
My user can delete/modify their articles, and then undo the changes thanks to the temporal table.
However, now I want to create a feature that allows user to delete an article permanently.
So I wonder if there is any way that we can remove record in Articles table, without inserting historical record into ArticlesHistory table?
I am trying to create one-to-one relationships between the a User and Archive table. I successfully achieved that using entity relationship diagram, but not in actual SQL code.
I wan to create these tables using SQL code like shown below, but at the same time defining its relationship with Table 2.
CREATE TABLE Table1
(
Some code
);
I had two models(Reporter and Article). I did
makemigrations
migrate
it created two tables in the database. Then I accidentally dropped the tables from the database.
Now, when I do migrate again, it says that the table does not exist. It does not create tables from models. The error message is:
relation "first_test_article" does not exist
What am I missing here?
Your last migration is that creates these tables?
The problem is that if you will migrate backwards to previous, exception will probably raise, because it will be trying to delete inexistent tables.
The way you can solve it is to create these tables (empty, without fields) by hands, then you should migrate backwards to previous migration. It will delete these tables, and then you will be able to migrate forwards and create these tables again.
I need to change the primary key (#Id) of an entity from natural key to a new field that represents a surrogate key (it will use #GeneratedValue(strategy=GenerationType.AUTO)).
What is the easiest way to update the database schema other than dropping the table and letting Hibernate to create it again?
I was trying to let Hibernate update the schema automagically with hibernate.hbm2ddl.auto set to update, but it didn't work out. I suppose that Hibernate autoupdate doesn't support such drastic changes of database schemas.
If it were only one entity, I'd
make the changes in the database manually (SQL)
and update the Hibernate mapping accordingly