DDD how to Communicate for search service

Question

I work on eCommerce app. I use micro-services with ddd. I have product service. It store title description etc. Pricing service store product prices and promotions. Category service store categories and product category. Shipment service store all about shipment data and product shipment details dweight cargo firm isFreeCargo etc.

I dont Want to use composition pattern for searching. I create search service which store all datas of services. Pricing, product information, shipment information, category information etc. I concat all data with events. Like cQRS So all services communicate each other with events.

my problem is; when CreateProductRequest come To product service . It includes categoryId, price, shipmentFirm etc. I mean not only product service information. I only save title description etc in product service. There is no data like Price or category in product service. because They dont belong this domain. When product created and event raise productCreatedEvent that includes created product id and other service informations come with request.price , category etc.

Other services listen this event. And consume. Pricing save productId and price. Cagegory save productId and categoryId ...

And search service consume event,too. But there is no data about price or category because they just published. Okey I can prove consistency with events when price change or category After saving. but at first maybe there is not going to be price or category for 2-3 sec. how canI save category and price for search service immediately. because there is no price and category denormalize and caculated data in productCreatedEvent .There is just reference Ids like categoryId or not caculated price.They are going to be exist on search service after own services save and publish events like ProductCategoryUpdated or ProductPriceCaculeted

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Answer 1

First of all. What I can see is that price and category services are very related to Product and they dont have strong functionality on its own so I suggest you to merge the three of them in one service. If the price service is used to create promotions, I would make a promotion service wich communicates with product service asking for the price of a product or a category of products, and apply them the corresponding discount.

The first problem has to do with what I have just said, because price, category and product are so related you have to pass all the data when you create a product, but because they are different services, product service should not be aware of this information. In case you want to do this way, you should create prices and categories independently of the product and when these are created each service should send a priceCreated or categoryCreated event that will be consume by anyone interested in. For example the search service.

For the second question, the best approach I think is the first one, first because It wont couple services. The cart service only have the ids no other information. And when you want to query another information you only have to make the query to the proper service as usual, so no coupling is created. And second, the main drawback of the second option is that you are including logic related to cart service in all the other service. For each one you have to listen events and instead of make logic related to the service like update some info, they are sending info to another service. It is like a hidden command message