How the Cart Validation Works in the Frontend

1) Basic Requirements

• The product must be configured as a rental item (tab Specifications → Rental).

• All relevant plugin settings (e.g. net/gross calculation, calendar, opening hours) must be saved.

• Afterwards, clear the cache if necessary.

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2) When clicking “Add to cart,” the plugin performs the following checks — in this order:

A. Date Overlap (always active, regardless of parallel rentals)

• The plugin checks whether the selected rental period overlaps with any existing reservation.

• If yes, and parallel rentals are not allowed (or Max. Parallel = 0/empty),

  the item cannot be added to the cart.

• The frontend displays an error message (snippet e.g. notAvailable).

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B. Parallel Rentals (only if enabled)

• If “Check parallel rentals” is enabled for the product, the plugin determines:

  • the already reserved quantity during the requested period (from the reservation table),

  • the quantity already in the current cart,

  • and the currently requested quantity.

• These values are added up to form the total planned quantity.

• If the total planned quantity exceeds the product’s setting for “Max. parallel rentals,”

  the addition to the cart is rejected.

• The error message shows the allowed maximum (snippet e.g. maxParallelDays).

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C. Quantity Limit per Add-to-Cart

• If the customer increases the quantity (e.g. “30 items”), this quantity is also included in the total planned quantity.

• Even if there are no items yet in the cart, the system blocks the addition if

  requested quantity + existing reservations > Max. Parallel.

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3) Examples

• Parallel rentals disabled

  An existing reservation: Oct 22 – Oct 28

  Requested period: Oct 21 – Oct 29 → Overlaps → Rejected (regardless of quantity).

• Parallel rentals = 2

  One reservation already exists.

  Customer adds quantity 2 → total = 1 + 2 = 3 > 2 → Rejected.

  Customer adds quantity 1 → total = 1 + 1 = 2 → Allowed.

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4) Display and Messages

• All error and info texts are managed via snippets (e.g. notAvailable, maxParallelDays, minDays, maxDays).

• This means all messages are fully translatable.

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5) Technical Overview (no code)

• The logic runs before the actual add-to-cart process.

• It considers both:

  • existing reservations in the requested period, and

  • items already in the current cart.

• Only if all checks pass will the rental item be added successfully.

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💡 Tester Tip:

Ensure the product is correctly configured as a rental item (prices, min/max days, parallel settings, etc.)

and clear the shop cache before testing — this ensures all configuration and snippet changes are applied properly.