add a fincancial balance for each stock taking

[mjavurek]

This PR adds a financial balance to each stock taking in the overview:

and in the detail view for each taking:

So the financial loss (or surplus) of stock takings can be considered in a financial balance.

[lentschi]

@mjavurek Thanks for your contribution!

I've added some code comments.
In addition to those: As a rule of thumb, sums shouldn't be done in the view, but in the controller.

[lentschi]

In general, building sums like this may raise performance issues.
If there are a larger number of stock_changes it might be less resource hungry to do this with a db function. Have you considered using sum?

[mjavurek]

yes a db function would be much more effective, I will try to implement it this way. I am not very familiar with this kind of programming and was glad that I could get working it this way on my local foodsoft installation to get the balances for our foodcoop...

[lentschi]

@mjavurek

I am not very familiar with this kind of programming

Admittedly what I'm suggesting here is quite complicated as we have to take article versioning into account (Something that your stock_change.stock_article automagically did, but with poor performance), so I looked into it myself - Adapting the StockTakings query in the controller's index action like this should work:

@stock_takings = StockEvent
                     .select(%(
                      `#{StockEvent.table_name}`.*,
                      SUM(
                         `#{StockChange.table_name}`.`quantity`
                         * (`#{ArticleVersion.table_name}`.`price` + (`#{ArticleVersion.table_name}`.`deposit`) * ((`#{ArticleVersion.table_name}`.`tax`) + 1))
                      ) AS balance
                     ))
                     .joins(stock_changes: { stock_article: [:article_versions] })
                     .joins(ArticleVersion.latest_outer_join_sql("#{Article.table_name}.#{Article.primary_key}"))
                     .where(later_article_versions: { id: nil })
                     .group('stock_event_id')
                     .order('date DESC')
                     .page(params[:page]).per(@per_page)

Then in the view you can use format_currency(stock_taking.balance) and remove the balance variable you introduced.

[mjavurek]

Thanks @lentschi for reviewing my code. Sorry for the missing initialization and my inefficient and unconventional programming style.

[lentschi]

Shouldn't there be a table heading for this new 'balance' column? 🤔

[lentschi]

Shouldn't there be a table heading for this new 'balance' column? 🤔