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Limit Order Line Quantity

How-To Guide to limit order line quantity in Umbraco Commerce.

In this guide, we will be looking at Validation events in Umbraco Commerce. These enabled you to limit order line quantity based on:

The existing stock value of the product, and
The existing quantity of the product in the cart.

ProductAddValidationHandler

When adding a product to the cart we need to verify that the product is in stock. We also need to verify that the customer does not already have the remaining quantities in the cart.

public class ProductAddValidationHandler : ValidationEventHandlerBase<ValidateOrderProductAdd>
{
    private readonly IProductService _productService;

    public ProductAddValidationHandler(IProductService productService)
    {
        _productService = productService;
    }

    public override void Validate(ValidateOrderProductAdd evt)
    {
        var order = evt.Order;
        var productReference = evt.ProductReference;

        var stock = _productService.GetProductStock(productReference);

        var totalQuantities = order?.OrderLines.Where(x => x.ProductReference == productReference).Sum(x => x.Quantity) ?? 0;

        if (stock.HasValue && totalQuantities >= stock.Value)
            evt.Fail($"Only {stock} quantities can be purchased for {productReference}.");
    }
}

OrderLineQuantityValidationHandler

When changing the order line quantity on the cart page, we need to ensure that the quantities being changed are in stock.

public class OrderLineQuantityValidationHandler : ValidationEventHandlerBase<ValidateOrderLineQuantityChange>
{
    private readonly IProductService _productService;

    public OrderLineQuantityValidationHandler(IProductService productService)
    {
        _productService = productService;
    }

    public override void Validate(ValidateOrderLineQuantityChange evt)
    {
        var orderLine = evt.OrderLine;
        var productReference = orderLine.ProductReference;

        var stock = _productService.GetProductStock(productReference);

        if (stock.HasValue && evt.Quantity.To > stock.Value)
            evt.Fail($"Only {stock} quantities can be purchased for {productReference}.");
    }
}

Register event handlers

Finally, we need to register the Umbraco Commerce event handlers via an IUmbracoCommerceBuilder extension.

public static class UmbracoCommerceUmbracoBuilderExtensions
{
    public static IUmbracoCommerceBuilder AddEventHandlers(IUmbracoCommerceBuilder builder)
    {
        // Register event handlers
        builder.WithValidationEvent<ValidateOrderProductAdd>()
            .RegisterHandler<ProductAddValidationHandler>();

        builder.WithValidationEvent<ValidateOrderLineQuantityChange>()
            .RegisterHandler<OrderLineQuantityValidationHandler>();

        return builder;
    }
}