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Exercise 5: Optional exercise

You can earn an additional +3 points with the completion of this exercise. (In the evaluation, you will see the text "imsc" in the exercise title; this is meant for the Hungarian students. Please ignore that.)

We will group the orders in this exercise by date. We would like to see how our company performs by comparing the sales across time. We will use a $bucket aggregation.

Requirements

The method to implement is OrderGroups GroupOrders(int groupsCount). This operation shall group the orders into groupsCount equal date ranges. The return value contains two values:

  • IList<DateTime> Thresholds: The threshold dates of the date ranges.
    • The lower bound of the interval is inclusive, while the upper bound is exclusive.
    • When having n intervals, the Thresholds list has n + 1 items
    • E.g.: Let the Thresholds be a, b, c, d; the intervals shall then be: [a, b[, [b, c[ and [c, d[.
  • IList<OrderGroup> Groups: The groups that fall into each date range. The properties of OrderGroup are:
    • Date: The start date of the interval. E.g., for the interval [a, b[ the value isa.
    • Pieces: The number of orders within the interval.
    • Total: The cumulative sum of the values of orders within this interval.

Further requirements:

  1. There should be exactly groupsCount intervals.
    • The number of items in Thresholds will be exactly groupsCount + 1.
    • The number of items in Groups is at most groupsCount — no need for an item for intervals with no orders
  2. The lower boundary should be the earliest date in the database
  3. The upper boundary should be the latest date in the database + 1 hour
    • This is needed because the upper boundary is exclusive. It ensures that every item in the database falls into one of the intervals.
    • Tip: add one hour to a date: date.AddHours(1).
  4. The intervals should be of equal size
    • Tip: C# has built-in support for date arithmetic using dates and the TimeSpan classes.

You can assume the following:

  • All orders in the database have Date values even though the type is nullable DateTime?.
    • You can use date.Value to get the date without checking date.HasValue.
  • groupsCount is a positive integer greater than or equal to 1.

Draft solution

  1. Get the earliest and latest order dates from the database.

    • Tip: You can execute two queries to get the values or a single aggregation.

  2. Calculate the interval boundaries according to the requirements.

    • This will yield the Thresholds list for the return value.

  3. Execute a $bucket aggregation on the orders collection. See the documentation here.

    • the groupBy expression will be the date of the order
    • boundaries expects the values as stated in the requirements; the list assembled in the previous step will work just fine
    • output should calculate the count and total value

    Tip

    If you receive an error message "Element '...' does not match any field or property of class..." then in the output expression, change every property to lowercase (e.g., Pieces -> pieces). It seems that the Mongo C# driver does not perform the required name transformations here.

  4. The $bucket aggregation will yield the intervals according to the specification. You will only need to transform the results into instances of OrderGroup and produce the return value.

  5. Use the Group orders link of the website to test your solution. A diagram will display the calculated information. Test your solution by changing the number of groups and adding orders in the past using the previously implemented Add new order functionality.

SUBMISSION

Create a screenshot of the web page displaying the diagram. Save the screenshot as f5.png and submit it with the other files of the solution. The screenshot shall show both diagrams (you may need to zoom out in the browser to fit them). Verify that your Neptun code is visible on the image at the bottom of the page! The screenshot is required to earn the points.

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