My class diagram needs to model a relationship with varying quantities

Question

I am trying to design a restaurant ordering system in UML, which should also include the stock system.

One of the classes is a Dish (i.e. a dish on the menu), and another is an Ingredient.

My initial idea was to place an aggregation of Ingredients within Dish, but I've also read that a many to many relationship is more appropriate.

My problem is that in this case, simply having a relationship isn't enough. For instance a Dish could have 30g of Ingredient A, while another Dish could have 20g of Ingredient A.

How can I model this kind of dependency in UML?

Answer 1

Create a Many to Many relationship; call it DishIngredients.

Include Amount and Units fields in DishIngredients; this will let you specify the amount (e.g. 30) and units (e.g. grams) for each Dish/Ingredient combination.

Answer 2

An Ingredient is a Product in a Recipe (or Dish) with it's Quantity (quantity should include Unit of Measure and be translatable between units). A Recipe contains many Ingredients. A Product can be in many Ingredients. And can be in Stock with a Quantity as well.