Reduce number of transactions for #mark_collection_as_read

[fatkodima]

Inner transactions are not necessary (if I'm not missing something obvious) and can be replaced as was done in this PR.

Fixes #80.

[coveralls]

Coverage remained the same at 100.0% when pulling bc716f0 on fatkodima:optimize-mark_collection_as_read into 6c7a1bd on ledermann:master.

[ledermann]

Thanks for your work, but this transaction seems to be needed for PostgreSQL. Please see here:
#78

[fatkodima]

@ledermann Yes, you are right. I should probably better read git history of changing files.
This, however, can be easily optimized for mysql and sqlite without using inner transactions. Implementation for postgresql should left as is with inner transactions.

What do you think, should I rework this or left for #95?

[ledermann]

Thanks @fatkodima, your commitment is is highly appreciated!

Implementing a DB switch to use inner transactions for PostgreSQL only seems a good improvement to me.

Regarding #95: I'd prefer to avoid adding a new gem dependency (upsert) into this little project.

[fatkodima]

Ok, I will update this PR with db switch.

Regarding #95: I'd prefer to avoid adding a new gem dependency (upsert) into this little project.

Yes, I'm not also a big fan of dependencies. Will appreciate, if you have suggestions of how that feature can be implemented in other ways.

[fatkodima]

@ledermann Updated this.

[ledermann]

Great work, thanks!