Use contextmanager for SQLite communication

[hoxbro]

Fixes #8

Also adds a close method to close the database connection.

[ahuang11]

I was wondering if you could simply call
with self.con to handle transactions?
https://blog.rtwilson.com/a-python-sqlite3-context-manager-gotcha/

(you probably know more about this than me)

Also, thoughts on using closing?
https://stackoverflow.com/questions/10029403/python-why-doesnt-writing-a-contextmanager-for-an-sqlite3-cursor-work

[codspeed-hq]

CodSpeed Performance Report

Merging #91 will not alter performance

_{Comparing use_context (1af7cc1) with main (1edf4ff)}

Summary

✅ 6 untouched benchmarks

[hoxbro]

Nothing is set in stone, haven't really tested it yet.

Having to open a connection for each of the commit could be slow, but I don't know.

#8 had closing in in it, didn't use it here because I needed more functionality in the context manager.

[ahuang11]

No I don't think it's opening a new connection each time; it's reusing the same connection with transactional things:
"""
Connection objects can be used as context managers that automatically commit or rollback transactions. In the event of an exception, the transaction is rolled back; otherwise, the transaction is committed.
"""
https://docs.python.org/3/library/sqlite3.html#how-to-use-the-connection-context-manager

[hoxbro]

There is a difference between the example in https://blog.rtwilson.com/a-python-sqlite3-context-manager-gotcha/ and https://docs.python.org/3/library/sqlite3.html#how-to-use-the-connection-context-manager.

The first creates a new connection in the context manager, and the latter uses an existing connection in the context manager, which can be used again. I suspect the latter does something similar to what I have done; it could be something only newer versions of Python support. I will check this tomorrow.

[hoxbro]

There is no significant difference between using self.con as a context manager and the implemented run_transaction. However, I have kept the run_transaction as it will use a cursor directly, which gives a bit of flexibility, like here (even though I think it is still possible by using self.con):

holonote/holonote/annotate/connector.py

Line 505 in 6257dd7

self.primary_key.validate(cursor.lastrowid, fields[self.primary_key.field_name])