nopCommerce - Create Customized Service that inherit from Core Service by Dependency Injection

Scope

Provide the cleanest way to inherit from nopCommerce core services without any tampering to the core files.

In this exercise, the Nop.Services project is 100% untouched. Why is it so important? It benefits in many different ways but mostly for the reason of keeping the code neat and manageable. A nice and clear separation between custom code and core code.

This is written base on nopCommerce 3.1, the latest version as of today it is written.

Business Requirements

• Discount should be calculated based on RRP (Product.Price), not the SpecialPrice or TierPrice. 
• PriceCalculationService.GetFinalPrice() should still return the cheapest price out of the following 3 conditions:-
• Cheapest discount off RRP
• Special Price
• Tier Price (if eligible / available)

Setup

We setup the price for the "Cooking for Two" book as follow. RRP $19, and Speical $15.

 We then apply discount rule 50% to the category.

50% discount applied to special price and now selling for $7.5. This is the default behavior of nopCommerce out of the box.

Implementation

I created a new project and added to the solution called TA.Services. It follows the same folder structure as Nop.Services and I created a new class CustomPriceCalculationService.

In TA.Services, I added reference Nop.Core and Nop.Services.

Similarly, in Nop.Web.Framework, I need to add reference to TA.Services.

Under Nop.Web.Framework, I changed this magic line in DependencyRegistrar.cs.

[EDIT] In TA.Services, I create a new DependencyRegistrar that implements IDependencyRegistrar. I will register my service to the interface. What it does is now everywhere in the project that require IPriceCalculationService, the IoC will return a concrete class CustomPriceCalculationService instead of the old PriceCalculationService.

In CustomPriceCalculationService, I need to inherit PriceCalculationService and implement IPriceCalculationService. Some usual Ctor methods override.

For those who interested in the actual implementation, I only made small changes to GetDiscountAmount and GetFinalPrice.

Now we are selling for $9.5 (50% off from $19). Hopefully still a happy customer!!

Conclusion

There are maybe better ways to implement this than what I have done here. eg. Use the plugin approach and make the use of Special Price configurable in the admin etc, but I couldn't wait to try this 100% clean way of customizations. 

Now I have a complete control on how I like to plug and play this customizations in a multi-tenant environment, or I can put more custom inheritance on top of already custom inheritance. The only thing I need to change is the DI which is pretty much given. 

As you can see, customization on services is a lot easier than controllers. Note how much troubles I had with the nopCommerce Customization with Controller Inheritance.