Handling of multiple values for one Quantity

[yeganer]

Currently we can associate multiple Quantities with one object, for example a line. In practice this might be useful when there is a theoretical and a measured value. However the current model makes interacting with the database very difficult.

I propose to change all relationships with quantities to One-to-One relationships as part of the Quantity rework that should be coming. One could then add both, a measured and a theoretical value, to the same quantity.
Then one could include the logic to decide which value should be used by default at one place and would not have to duplicate it several times.