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Here a customer can submit an order for one or many products . so, there is a one to many relation between customer_order and customer_ordered_products entities. Inside customer_ordered_products a product is uniquely distinguished by two attributes (product_category and product_id ). product_category is simply name of one of the five entities (sports_equipments, appliances, clothes, electronics, office_supplies ) representing different products. So, for each entry in customer_ordered_products I can have maximum one product_id and one product_category . But as only one product_id from the five entities can be present in the customer_ordered_products entity, so that relation is many to zero or one.

The problem is, when I think all of the zero to one relation to be zero there would be no product_id & when I consider two or more of them to be one(1) then there would be multiple values for a single valued attribute .

In this diagram I could use a product entity instead of five entities having product_category distinguishing different categories .That would solve the problem. But I do want to implement this diagram with different entities for different categorized products and solve this problem too.

  • Is there a reason for splitting the "product" entity into 5 entities? Why not just 1? – ypercubeᵀᴹ Nov 13 '17 at 9:26
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The telling part is where you said "But as only one product_id from the five entities can be present in the customer_ordered_products"

I could fix this by putting a product_category on the customer_order (a "default" if you will) and add a constraint between customer_ordered_products.product_category and customer.product_category that ensures they are the same value.

Another way to do it, if you can, is to remove the product_category from the customer_ordered_products and simple join customer_orders to customer_ordered_products everytime you needed to get that 1 applicable value of product_category.

Hope this helps.

  • I can't add attribute product_category to customer_ordered_products as one order can have multiple products from multiple categories . That's why customer_order & customer_ordered_products are related by one to many . – Utshaw Nov 14 '17 at 17:31

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