Allow choosing date for conversions

[dvorak0]

A minimal example is

plugin "beancount.plugins.auto_accounts"
option "operating_currency" "CNY"

2016-01-01 price HKD                                 0.8 CNY
2019-01-01 price HKD                                 0.9 CNY

2016-01-02 * "Someone"
  Assets:Bank -10000 HKD
  Expenses:Buy +10000 HKD
  
2019-01-02 * "Someone"
  Assets:Bank -10000 HKD
  Expenses:Buy +10000 HKD

I choose 'Converted to CNY' and see

, which works very well as 18000 CNY = 20000 HKD * 0.9 HKD/CNY.

However, it's not the case in account view:

, where although the final balance(18000 CNY) is correct, the accumulation is confusing (1+2 != 3).

The reason I guess is that the first transition uses the price on 2016-01-01.

[yagebu]

I find this to be consistent. I think it's sensible that the transaction date is used to look up the price. Then of course the converted sums might not match the sum of the converted values.

[dvorak0]

@yagebu thanks. So would you modify it or add a new option? If not, could you please point me where I can modify the code to fit my needs?

[yagebu]

So would you modify it or add a new option?

I think you misunderstood - I find the current behaviour to be consistent: "I think it's sensible that the transaction date is used to look up the price."

Which behaviour would you suggest instead?

[dvorak0]

I expect to see the looked up prices are the same for this query, e.g. the latest price which is 0.9 in the example. The current implementation is looking up the price for each transaction instead of for the query.

One price for the query and all of the transactions will give 1 + 2 = 3(9000+9000=18000) in the figure. Then the converted sums MATCH the sum of the converted values.

[yagebu]

I think we should keep the current behaviour as default, but we can add the date as an additional parameter for the conversion option to force one date to be used for all conversions.

[dvorak0]

That would be helpful!