Duplicated Deductions in Payroll Calculation

[unreal0901]

Environment

• Python Version: 3.11.9
• Operating System: Windows 11 Pro

Issue Description

When calculating payroll deductions, duplicate entries appear in the results for employees with specific deduction assignments.
I'm not sure if this behavior is intended, but I believe each deduction should be applied only once.

Additionally, there is another issue: when creating a deduction and specifying it for a particular employee, the Include_all_active_employees boolean is automatically set to True in the database by default.

Files

payroll -> methods -> payslip_calc.py

Url

    path("create-payslip", component_views.create_payslip, name="create-payslip"),

Steps to Reproduce

1. Create an employee.
2. Create a contract.
3. Attach a filing to the contract.
4. Create a deduction.
5. Apply the deduction to specific employees.
6. Generate a payslip – duplicate deductions appear for each employee.
7. When installments are present, a TypeError occurs.

Debug Output

Specific Deductions:
ID: 8
Conditional Deductions:
Active Employee Deductions:
ID: 8
All Deductions:
ID: 8
ID: 8

The output shows the same deduction (ID: 8) appearing multiple times in the final result.

Proposed Solution

1. Fix duplicate deductions

   • Add .distinct() when combining querysets:

   deductions = (specific_deductions | conditional_deduction | active_employee_deduction).distinct()

2. Fix queryset merge errors

   • Add .distinct() to both installment querysets:

   installments = deductions.filter(is_installment=True).distinct()

   • Use IDs instead of directly merging querysets:

   pretax_ids = list(pretax_deductions["installments"].values_list("id", flat=True))
   posttax_ids = list(post_tax_deductions["installments"].values_list("id", flat=True))
   all_ids = list(set(pretax_ids + posttax_ids))
   installments = models.Deduction.objects.filter(id__in=all_ids)

3. Ensure consistent use of .distinct()

   • Apply .distinct() across all relevant querysets.
   • Use distinct querysets in both calculate_pre_tax_deduction and calculate_post_tax_deduction to prevent TypeErrors when merging non-unique querysets with unique querysets.

[horilla-opensource]

Hi @unreal0901 ,

Thank you for reporting this issue.

We acknowledge the problem of duplicate deduction entries and the unexpected behavior of the Include_all_active_employees field. Your detailed explanation and proposed solution are greatly appreciated.

We'll review the suggested fixes, including the use of .distinct() across querysets and the approach to merge deductions by IDs. This will help ensure accurate payroll calculations and prevent TypeErrors.

We'll update you once the fix is implemented. Thank you for contributing to improving Horilla!

Best Regards,
Team Horilla