具有多个多对多约束的库存数据库设计？

Question

I'm trying to design a database architecture for a simple inventory program.

This inventory will consist of items in boxes. Boxes contain items, and are items themselves.

I imagine box will be a super type of item .

My main hangup is how to structure/constrain the relation between boxes so that I can still constrain the unique condition that an item can only be in one "place" at a time.

I know that many-to-many relations should let me know which items are in which boxes, but what about boxes that are in other boxes?

For instance:
Box A contains Item B and Box C . Box C contains Item D .

How can I design a system that when I look for Item D I will find it inside Box A and Box C (really great if I could also know how the relation of the boxes -- latter is inside the former).

Answer 1

You can use the self relationship with the table itself. You can mention below mentioned columns in your database design:

ItemId(PK)
ItemName
ItemType(Can be B for Box and I for item)
ItemContainer(Will contain ItemId from this table itself and will be null if it is not present in any box, if required add check constraint that if itemType is I then it cannot be null)

You can place the data as:

ItemId      ItemName      ItemType     ItemContainer
  1         BoxA             B            (null)
  2         BoxB             B               1
  3         ItemA            I               2

Since ItemId is a primary key, thus, database will allow only one row per item and thus, it will be available only in one box.

Check if this design helps...