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When I delete all the item's from my query in Django the item id's don't reset [duplicate]

I have been working on an offline version of my Django web app and have frequently deleted model instances for a certain ModelX.
I have done this from the admin page and have experienced no issues. The model only has two fields: name and order and no other relationships to other models.
New instances are given the next available pk which makes sense, and when I have deleted all instances, adding a new instance yields a pk=1, which I expect.
Moving the code online to my actual database I noticed that this is not the case. I needed to change the model instances so I deleted them all but to my surprise the primary keys kept on incrementing without resetting back to 1.
Going into the database using the Django API I have checked and the old instances are gone, but even adding new instances yield a primary key that picks up where the last deleted instance left off, instead of 1.
Wondering if anyone knows what might be the issue here.

I wouldn't call it an issue. This is default behaviour for many database systems. Basically, the auto-increment counter for a table is persistent, and deleting entries does not affect the counter. The actual value of the primary key does not affect performance or anything, it only has aesthetic value (if you ever reach the 2 billion limit you'll most likely have other problems to worry about).
If you really want to reset the counter, you can drop and recreate the table:
python manage.py sqlclear <app_name> > python manage.py dbshell
Or, if you need to keep the data from other tables in the app, you can manually reset the counter:
python manage.py dbshell
mysql> ALTER TABLE <table_name> AUTO_INCREMENT = 1;
The most probable reason you see different behaviour in your offline and online apps, is that the auto-increment value is only stored in memory, not on disk. It is recalculated as MAX(<column>) + 1 each time the database server is restarted. If the table is empty, it will be completely reset on a restart. This is probably very often for your offline environment, and close to none for your online environment.

As others have stated, this is entirely the responsibility of the database.
But you should realize that this is the desirable behaviour. An ID uniquely identifies an entity in your database. As such, it should only ever refer to one row. If that row is subsequently deleted, there's no reason why you should want a new row to re-use that ID: if you did that, you'd create a confusion between the now-deleted entity that used to have that ID, and the newly-created one that's reused it. There's no point in doing this and you should not want to do so.

Did you actually drop them from your database or did you delete them using Django? Django won't change AUTO_INCREMENT for your table just by deleting rows from it, so if you want to reset your primary keys, you might have to go into your db and:
ALTER TABLE <my-table> AUTO_INCREMENT = 1;
(This assumes you're using MySQL or similar).

There is no issue, that's the way databases work. Django doesn't have anything to do with generating ids it just tells the database to insert a row and gets the id in response from database. The id starts at 1 for each table and increments every time you insert a row. Deleting rows doesn't cause the id to go back. You shouldn't usually be concerned with that, all you need to know is that each row has a unique id.
You can of course change the counter that generates the id for your table with a database command and that depends on the specific database system you're using.

If you are using SQLite you can reset the primary key with the following shell commands:
DELETE FROM your_table;
DELETE FROM SQLite_sequence WHERE name='your_table';

Another solution for 'POSTGRES' DBs is from the UI.
Select your table and look for 'sequences' dropdown and select the settings and adjust the sequences that way.
example:

I'm not sure when this was added, but the following management command will delete all data from all tables and will reset the auto increment counters to 1.
./manage.py sqlflush | psql DATABASE_NAME

pymysql - Clear a table for testing

I'm looking to write tests for my application. I would like to work with a clean database for all my tests. For various reasons, I cannot create a separate test database.
What I currently do is run everything in a transaction and never commit to the db. However some tests read from the db, so I'd like to delete all rows at the start of the transaction and start from there.
The problem I am running into is with foreign key constraints. Currently I just go through each table and do
cursor.execute("DELETE FROM %s" % tablename)
which gives me
IntegrityError: (1451, u'Cannot delete or update a parent row: a
foreign key constraint fails (`testing`.`app_adjust_reason`,
CONSTRAINT `app_adjust_reason_ibfk_2` FOREIGN KEY (`adjust_reason_id`)
REFERENCES `adjust_reason` (`id`))')
edit: I would like something generic that could be applied to any database. Otherwise I would specifically drop the constraints

A more general approach is to create a database from scratch before the test run and drop it after, use CREATE DATABASE_NAME and DROP DATABASE_NAME. This way, you are always starting with a clean database state and you would not worry about the foreign key or other constraints.
Note that you would also need to create your table schema and (possibly test data) after you create a database.
As a real world example, this is what Django does when you run your tests. The table schema is recreated by the Django ORM from your models, then the fixtures or/and the schema and data migrations are applied.

Django add new entry from admin panel

I'm trying to add a new entry by using the admin panel in Django
The problem is that I've already populated my DB with 200 records and if I try to add a new entry from admin I get a duplicated key error msg that keep increasing whenever I try the process again
error:
duplicate key value violates unique constraint "app_entry_pkey"
admin.py:
admin.site.register(Entry)
model:
class Entry(models.Model):
title = models.CharField(max_length=255)
url = models.TextField(max_length=255)
img = models.CharField(max_length=255)
def __unicode__(self):
return self.title

If you created the database table using Django, then most likely your auto_increment value was not updated when you imported the data outside of Django.
It may also be that when you imported the data you did not give the 200 records each their own unique primary key. I think that (some versions of) SQLite will sometimes allow that in mass imports.
MySQL
For example, I’m looking at a MySQL table in Sequel Pro and see that it has an “auto_increment” value of 144. This means that the next primary key value will be 144.
You can see this value for your table (in MySQL) using:
SHOW TABLE STATUS FROM databaseName where name="entry"
Replacing “databaseName” with the name of your Django database. Other database software will likely have different syntax.
You can set the next auto_increment value (in MySQL) using:
ALTER TABLE databaseName.entry AUTO_INCREMENT ###
Again replacing databaseName with the name of your database; and as before, the syntax may vary depending on the database software you’re using.
If this doesn’t help, you may find it useful to show the table’s status and copy that into your question. This might also be useful in tracking down the issue:
SHOW CREATE TABLE databaseName.entry
Postgres
In Postgres, you can get the current value of the auto increment variable (called sequences in Postgres) using something like:
SELECT last_value FROM app_entry_pkey;
And you will likely set it to a new value with something like:
ALTER SEQUENCE app_entry_pkey RESTART WITH ###
or
SELECT setval('app_entry_pkey', ###)
Note, though, that I do not have a Postgres database handy to test these on. You may also find the following commands useful:
SELECT MAX(id) FROM entry
SELECT nextval('app_entry_pkey')
The latter should generally be larger than the former, and note that “id” is the name of the column in your “entry” model’s table; it may be different in your table. See http://www.postgresql.org/docs/8.1/static/functions-sequence.html for more information.

In South, can I copy the value of an old column to a new one?

One of my Django models is a subclass and I want to change its superclass to one that is very similar to the original one. In particular, the new superclass describes the same object and has the same primary key. How can I make South create the new OneToOne field and copy the values from the old one to the new one?

In south, there are two kinds of migrations: schema migrations and data migrations.
After you've created the schemamigration, create a corresponding data migration:
./manage.py datamigration <app> <migration_name>
Do not run the migration (yet). Instead, open up the migration file you just created.
You'll find the method named forwards(). Into this you define the procedure by which values from old tables get copied to new tables.
If you're changing the structure of a given table to a more complex layout, a common method is to have two schema migrations around a data migration: the first schema migration adds fields, the data migration translates the old fields to the new fields, and the second schema migration deletes the old fields. You can do just about anything with the database with the forwards() method, so long as you keep track of which schema (previous or current) you're accessing. Generally, you only read from the orm.-related, and write to the traditional Django accessors.
The South Data Migration Tutorial covers this in some detail. It shows you how to use South's orm reference to access the database using the schema prior to the schema migration and gives access to the database without Django complaining about fields it doesn't understand.
If you're renaming a class, that can be tricky-- it involves creating the new table, migrating from one to the other, and deleting the old table. South can do it, but it might take more than one pass through shifting schemas and data migrations.
South also has the backwards() method, which allows you to return your database tables to a previous step. In some cases, this may be impossible; the new table may record information that will be lost in a downgrade. I recommend using throwing an exception in backwards() if you're not in DEBUG mode.

How do I delete in Django? (mysql transactions)

If you are familiar with Django, you know that they have a Authentication system with User model. Of course, I have many other tables that have a Foreign Key to this User model.
If I want to delete this user, how do I architect a script (or through mysql itself) to delete every table that is related to this user?
My only worry is that I can do this manually...but if I add a table , but I forget to add that table to my DELETE operation...then I have a row that links to a deleted, non-existing User.

As far as I understand it, django does an "on delete cascade" by default:
http://docs.djangoproject.com/en/dev/topics/db/queries/#deleting-objects

You don't need a script for this. When you delete a record, Django will automatically delete all dependent records (thus taking care of its own database integrity).
This is simple to test. In the admin, go to delete a User. On the confirmation page, you'll see a list of all dependent records in the system. You can use this any time as a quick test to see what's dependent on what (as long as you don't actually click Confirm).
If you perform deletions from your view code with .delete(), all dependent objects will be deleted automatically with no option for confirmation.
From the docs:
When Django deletes an object, it
emulates the behavior of the SQL
constraint ON DELETE CASCADE -- in
other words, any objects which had
foreign keys pointing at the object to
be deleted will be deleted along with
it.