Proposal to Improve Code Readability and current_position Handling in CursorPagination

[bae-code]

Hello,
I'd like to propose some changes to improve code readability and the handling of current_position in the CursorPagination class by addressing variable naming confusion.

Background and Problem

• The current code uses the variables reverse and self.cursor.reverse interchangeably, and is not clearly distinguishable from is_reversed.
• The condition current_position is not None is used repeatedly throughout the code, which reduces readability.
• By assigning this condition to a variable, we can improve code readability and make maintenance easier.

Proposed Changes

1. Assign current_position is not None to a Variable

• Declare a variable has_current_position = current_position is not None to reduce the repetitive use of the condition.

2. Rename variables to make their purposes clearer

• reverse → cursor_reverse (represents the client's request direction)
• is_reversed → is_ordering_reversed (represents the ordering field's direction)
• However, within the method, it's appropriate to use self.cursor.reverse to utilize the object's state, so we keep it as is.

3. Separated Sorting and Filtering Logic

• Created the filter_queryset_by_cursor method to separate the filtering logic from paginate_queryset.
• The paginate_queryset method now handles ordering and checks the existence of current_position, while the filter_queryset_by_cursor method handles the filtering based on the cursor position.
• This separation enhances modularity, reusability, and readability of the code.

Current Code:

if self.cursor is None:
            (offset, reverse, current_position) = (0, False, None)
        else:
            (offset, reverse, current_position) = self.cursor
...

if reverse:
    queryset = queryset.order_by(*_reverse_ordering(self.ordering))
else:
    queryset = queryset.order_by(*self.ordering)

if current_position is not None:
            order = self.ordering[0]
            is_reversed = order.startswith('-')
            order_attr = order.lstrip('-')

            # Test for: (cursor reversed) XOR (queryset reversed)
            if self.cursor.reverse != is_reversed:
                kwargs = {order_attr + '__lt': current_position}
            else:
                kwargs = {order_attr + '__gt': current_position}

            queryset = queryset.filter(**kwargs)
    ....

self.has_next = (has_current_position) or (offset > 0)
self.has_previous = (current_position is not None) or (offset > 0)

Modified Code Example:

def filter_queryset_by_cursor(self, queryset, current_position):
        order = self.ordering[0]
        is_ordering_reversed = order.startswith('-')
        order_attr = order.lstrip('-')

        # Test for: (cursor reversed) XOR (queryset reversed)
        if self.cursor.reverse != is_ordering_reversed:
            comparison_operator = '__lt'
        else:
            comparison_operator = '__gt'
        kwargs = {order_attr + comparison_operator: current_position}
        return queryset.filter(**kwargs)

def paginate_queryset(self, queryset, request, view=None):
        if self.cursor is None:
            (offset, cursor_reverse, current_position) = (0, False, None)
        else:
            (offset, cursor_reverse, current_position) = self.cursor
       ...
            
        if cursor_reverse:
            queryset = queryset.order_by(*_reverse_ordering(self.ordering))
        else:
            queryset = queryset.order_by(*self.ordering)
        if has_current_position:
            queryset = self.filter_queryset_by_cursor(queryset=queryset, current_position=current_position)    
      ...

self.has_next = has_current_position or (offset > 0)
self.has_previous = has_current_position or (offset > 0)

Benefits of the Changes

Improved Code Readability:

• By declaring has_current_position, we reduce the repetitive use of the condition and enhance code clarity.
• Renaming variables eliminates confusion between reverse and self.cursor.reverse, making the purpose of each variable clear.

Enhanced Code Structure:

• Separating the filtering logic into the filter_queryset_by_cursor method increases modularity and reusability.
• The paginate_queryset method is now more focused on its primary responsibilities.

Request for Feedback:

I believe these changes will have a positive impact on the project.
I would appreciate any feedback or suggestions from the maintainers and the community.
Please let me know if you have any thoughts or additional ideas.