add new data model minter and migration file and tests

[jsjiang]

@rushirajnenuji @datadavev Hi Dave and Rushiraj,
I refactored the minter data model a little bit and attached a few tests. Please review and let me know if you have questions.

Thank you

Jing

[jsjiang]

SQL query from the new '0003' migration file:

ezid % python manage.py sqlmigrate ezidapp 0003
--
-- Create model Minter
--
CREATE TABLE `ezidapp_minter` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `prefix` varchar(255) NOT NULL UNIQUE, `minterState` json NOT NULL, `createTime` integer NOT NULL, `updateTime` integer NOT NULL);
--
-- Alter field status on binderqueue
--
--
-- Alter field status on crossrefqueue
--
--
-- Alter field status on datacitequeue
--
--
-- Alter field status on searchindexerqueue
--
CREATE INDEX `ezidapp_minter_createTime_dfbbf01f` ON `ezidapp_minter` (`createTime`);
CREATE INDEX `ezidapp_minter_updateTime_a91cebee` ON `ezidapp_minter` (`updateTime`);

[datadavev]

The modified and create time stamp functionality needs to be checked. Should also try and add more tests for minter functionality to verify it operates correctly after restoration from the database.

[datadavev]

Here default is set to the value when default_time is executed, which is when the python interpreter loads the file, not when the class is instantiated. Should probably use the Django ORM mechanisms for auto timestamps, e.g. auto_now_add and auto_now.

[jsjiang]

From Django doc on Field.default

The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.

[datadavev]

It would be a callable if it was default=default_time, but as it is, you get a static value evaluated when the module is loaded.

[jsjiang]

Since the createTime and updateTime are int, we cannot use auto timestamps. How about just set the default value to zero and have business logic to handle the real values?

[datadavev]

ok, try it with default=default_time (i.e. without parentheses). It should work since it says that default is the callable default_time

[jsjiang]

default=default_time (i.e. without parentheses) worked! Thank you Dave.

[datadavev]

As for createTime.

[datadavev]

Here t2 should always be > t1. Suggest adding a brief delay (e.g. time.sleep(0.1)) before line 71.

[rushirajnenuji]

During the dev-sync call with @jsjiang, we reviewed this and Jing made modifications as per @datadavev's suggestions. We tested the changes and this looks good.

[jsjiang]

@datadavev @rushirajnenuji Thank you Dave and Rushiraj for reviewing and providing feedback. I have changed the code to use default=default_time for both createTime and updateTime and have adjusted tests. Please review.

Thank you

Jing

[jsjiang]

Pack this change to the BDB minter migration package and release at the same time.