C#•2y ago

❔ EF Core Code-first relationships

Hi there, I am trying to create a coffee vending machine application. But, I can't quite work the relationships around my head. The project requires to have pre-defined coffees (espresso, macchiato, latte, etc.) so that the user would be able to pick from, and characteristics (sugar, milk, creamer, etc.) that can be added to a picked coffee. I've created the following entities:

public class Coffee
    {
        [Key]
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required] 
        [StringLength(50)] 
        public string Name { get; set; }
        [Required] 
        [StringLength(400)] 
        public string Description { get; set; }
        public int Stock { get; set; }
    }

public class Coffee
    {
        [Key]
  [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required] 
        [StringLength(50)] 
        public string Name { get; set; }
        [Required] 
        [StringLength(400)] 
        public string Description { get; set; }
        public int Stock { get; set; }
    }

public class Characteristic
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required] 
        [StringLength(50)] 
        public string Name { get; set; }
        public int Stock { get; set; }
    }

public class Characteristic
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required] 
        [StringLength(50)] 
        public string Name { get; set; }
        public int Stock { get; set; }
    }

I want to be able to store the created coffees linked with the chosen characteristics in a separate table "SoldCoffes". To my understanding, I need to have one-to-many relationship, but I'm kind of stuck on this one. Any help would be appreciated.

11 Replies

Shinyshark•2y ago

So if I understand correctly, you want to create a One-To-Many relationship where you save a sold coffee and all of its characteristics? Like an Espresso with sugar, milk and creamer or a Latte with milk

Angius•2y ago

I'd have a table with types, a table of characteristics, and a table of drinks where each has a type and a bunch of characteristics 1-n between drink and type, n-m between drink and characteristic

_apixOP•2y ago

Yes, that's right This would result in a junction table: | DrinkId | CharacteristicId | How would I be able to differentiate multiple drinks created with same Id? Or am I just not seeing it right...

Angius•2y ago

Every kind of a drink would have a different ID, wym?

Shinyshark•2y ago

No his coffee, espresso and latte are individual drinks.

Angius•2y ago

And I proposed a different structure

Shinyshark•2y ago

He wants a transactional history of what drink was ordered with what characteristics

Angius•2y ago

Ah, well, in that case just make my Drinks table a History table One way or another, it should reference the drink and the modifiers

Shinyshark•2y ago

@_apix If you want to store each individual sale of a coffee with its characteristics I would recommend you use that junction table but you add one additional column to keep the rows grouped. Perhaps on a SaleId that starts from 1 and goes up by 1 each time you sell another coffee. Because you have one coffee with many characteristics, you won't know if you will have to insert 1, 2 or 3 rows. so you'd have to track that SaleId yourself.

_apixOP•2y ago

Thank you very much for the help guys. My concern was having 3 or 4 tables for this. But the fourth one is needed to keep track of created coffees.

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ EF Core Code-first relationships