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The LoanService class handles all loan-related business logic, including validation, creation, approval, and returns.

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Methods

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can_request_laptop

Validates whether a user can request a laptop based on their current loans.
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user_id
int
required
The ID of the user requesting the laptop
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can_request
tuple[bool, str]
Returns a tuple containing:
  • bool: True if user can request, False otherwise
  • str: Message explaining the result
Business Rules:
  • Users cannot have more than one active computer loan
  • Checks for loans in states: ‘pendiente’, ‘activo’, ‘atrasado’
  • Only applies to items in ‘computo’ category
Example: 
from app.services.loan_service import LoanService

can_request, message = LoanService.can_request_laptop(user_id=123)
if not can_request:
    flash(message, 'warning')
Error Messages:
  • "Ya tienes un equipo pendiente, en uso o atrasado." - User has an active computer loan
  • "Ok" - User can proceed with request

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can_request_accessory

Validates whether a user can request an accessory based on their current loans.
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user_id
int
required
The ID of the user requesting the accessory
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can_request
tuple[bool, str]
Returns a tuple containing:
  • bool: True if user can request, False otherwise
  • str: Message explaining the result
Business Rules:
  • Users are limited to 2 simultaneous accessories
  • Excludes ‘computo’ and ‘libro’ categories
  • Checks for loans in states: ‘pendiente’, ‘activo’, ‘atrasado’
Example: 
can_request, msg = LoanService.can_request_accessory(current_user.id)
if not can_request:
    flash(msg, 'warning')
    return redirect(url_for('main.index'))
Error Messages:
  • "Has alcanzado el límite de 2 accesorios simultáneos." - User has reached the limit
  • "Ok" - User can proceed with request

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create_loan

Creates a new loan record for a specific item instance.
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user_id
int
required
The ID of the user requesting the loan
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instance_id
int
required
The ID of the specific item instance being loaned
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environment
str
default:"None"
The environment where the loan will be used (e.g., ‘sala’, ‘externo’)
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days
int
default:"15"
Number of days for the loan period
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loan
Loan
Returns the newly created Loan object with status ‘pendiente’
Important Notes:
  • Does NOT commit the transaction - the controller must handle db.session.commit()
  • Sets initial status to ‘pendiente’ (pending approval)
  • Automatically calculates due_date based on days parameter
  • Creates the loan tied to a physical item instance
Example: 
try:
    for inst_id in reserved_ids:
        LoanService.create_loan(
            user_id=current_user.id,
            instance_id=inst_id,
            environment='externo',
            days=15
        )
    db.session.commit()
    flash('Solicitud enviada correctamente.', 'success')
except Exception as e:
    db.session.rollback()
    flash('Error al generar el préstamo.', 'danger')
Source Reference: app/services/loan_service.py:30

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approve_loan

Approves a pending loan and activates it.
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loan_id
int
required
The ID of the loan to approve
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result
tuple[bool, str]
Returns a tuple containing:
  • bool: True if approved successfully, False otherwise
  • str: Success or error message
Business Logic:
  • Only loans with status ‘pendiente’ can be approved
  • Sets status to ‘activo’
  • Records approval_date as current UTC time
  • Commits the transaction automatically
  • Item instance status should already be ‘prestado’ from reservation
Example: 
success, msg = LoanService.approve_loan(loan_id=456)

if success:
    flash(msg, 'success')
    return redirect(url_for('admin.admin_dashboard', status='activo'))
else:
    flash(msg, 'danger')
    return redirect(url_for('admin.admin_dashboard', status='pendiente'))
Error Messages:
  • "Préstamo no válido o ya procesado." - Loan doesn’t exist or is not pending
  • "Préstamo aprobado con éxito." - Approval successful
Source Reference: app/services/loan_service.py:49

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return_loan

Processes the return of a loaned item.
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loan_id
int
required
The ID of the loan to return
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result
tuple[bool, str]
Returns a tuple containing:
  • bool: True if returned successfully, False otherwise
  • str: Success or error message
Business Logic:
  • Only loans with status ‘activo’ or ‘atrasado’ can be returned
  • Calculates and records final penalty if loan is overdue
  • Sets status to ‘devuelto’
  • Records return_date as current UTC time
  • Releases the item instance back to ‘disponible’ status
  • Commits the transaction automatically
Example: 
success, msg = LoanService.return_loan(loan_id=789)

if success:
    flash('Ítem devuelto y reingresado al inventario con éxito.', 'success')
else:
    flash(f'Error: {msg}', 'danger')
Important: This method automatically handles penalty calculation for overdue items using the loan.is_overdue property and loan.penalty_fee calculation. Error Messages:
  • "Préstamo no válido o no está activo." - Loan doesn’t exist or wrong status
  • "Artículo devuelto exitosamente al inventario." - Return successful
Source Reference: app/services/loan_service.py:63

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check_overdue_loans

Scans for active loans past their due date and marks them as overdue.
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count
int
Returns the number of loans marked as overdue
Business Logic:
  • Queries all loans with status ‘activo’ where due_date < current time
  • Updates each to status ‘atrasado’
  • Commits changes if any loans were updated
  • Typically run as a scheduled background task
Example: 
count = LoanService.check_overdue_loans()
if count > 0:
    current_app.logger.info(f'{count} préstamos marcados como atrasados')
Usage: This method is typically called by a scheduler (APScheduler) to run periodically: 
from app.services.loan_service import LoanService

def scheduled_check():
    with app.app_context():
        count = LoanService.check_overdue_loans()
        print(f"Checked overdue loans: {count} updated")
Source Reference: app/services/loan_service.py:83