How to calculate the average cost and how to link it to a document?

Question

1C

How to implement links in documents, is it possible to do without manual editing of the module?
The task itself - It is
required to implement a configuration for an aquarium fish store:
3 types of documents must be implemented in the configuration:
Document "Purchase of fish":
Tabular part: Aquarium (Reference book), Species of fish (Reference book), Quantity, Purchase price, Amount
Document "Sale fish":
Tabular part: Aquarium (Reference book), Species of fish (Reference book), Quantity, Selling price, Amount
Document "Food purchase"
Document header: Aquarium (Reference book), Feed cost
The purpose of creating a configuration is to report on the profit received as a result of the sale of fish. At the same time, the cost of sold fish is calculated "according to the average" at the time of their sale. The cost of feed increases the cost of fish in proportion to the quantity.
Example:
We purchased:
2 Minor fish for 50 hryvnias in Aquarium 1
2 Mecherot fish for 100 hryvnias in Aquarium 1
2 Mecherot fishes for 100 hryvnias in Aquarium 2 After
 that we bought food for aquarium 1 for 100 hryvnias, for aquarium 2 for 30 hryvnias
which we sold 1 Mecherot from Aquarium 1 for 200 hryvnia and 1 from aquarium 2 also for 200 hryvnia.
Calculate the cost of fish and profit from the sale. Reflect the results in the report.
Report Form:
Aquarium
Fish Breed
Quantity
Sales Amount
Cost Price
Profit
Building the architecture of the configuration is left to the tester, optimal planning of metadata will also be an additional plus.
Finally stuck

Answer 1

First of all, what is the purpose of this question?
1) Get the final solution to your test task and some smart ideas to shine in the interview?
2) Or get an explanation on the mechanisms that seemed complicated / confusing to you?
I warn you that if the answer is No. 1, then this question and its answers are most likely not interesting to anyone except you and fall under the reason for deleting "This is a task, not a question."
In general, the task is very simple with an obvious solution. But I have comments on the director and his requirements for the document. Literally following the letter TK will lead to the following problematic situation. At some point, all the fish from a particular aquarium were sold (or temporarily transplanted to clean this aquarium). Just at that time, the food ordered in advance for this aquarium arrived (document "Purchase of food" with the cost of this food). The fish were launched the next day and began to be fed with purchased food. As a result, the cost of feed was written off, and the cost of fish (despite the high cost of their food) will be equal to the cost of their purchase. There is also a chance that the food will run out in another aquarium, and a new one has not yet been brought in - they will feed this aquarium with food.
The solution depends on the nature of the processes and the laziness of the users. I would prefer to create a "Fish Feeding" document that would indicate the weight of the food that was poured into a particular tank. The specific additional cost of fish in each aquarium is known - everything is clear as in a pharmacy.
The second solution is that we can calculate the final cost not when buying food, but then something like closing the month, which will analyze the cost of fish from the previous calculation and the amount of food purchased during the period, and then adjust the data on the cost of fish at the moment sales (directly in the postings of the document "Sale of fish") and will fix the current cost at the end of the billing period in an additional cost register. The data from this register will be used at the next month-end closing and in reports on the approximate value of the current balance of fish and the approximate profit within the non-closed period (I remind you that in the closed period the data in each sales document will already be updated).