Elasticsearch-如何设置N对N关系

Question

I am trying to create a Books library application. A user can borrow many books. A book can be borrowed by many users in its lifetime. In ElasticSearch there will be user documents and book documents. How can I search for all books that a user borrowed?

1. If I create a user-book document, then the book details are repeated as many times as the book is borrowed.

2. If I have an array in Book document listing all the users that borrowed the book, then the array will be enormous for popular books.

Which is better? or is there a simpler and better solution that the above 2?

Answer 1

Main question is IMHO what do you want to search?

1. If you want to search for books (title, isbn...), then store books.
2. If you want to search for Users (name, address, city...), then store users.
3. If you want to search for users that borrow a book, then store a user and an array of borrowed books.

That means that if you need 1 and 3, you will store twice the information about your book (one time in book type and another time in user type).

If you need to add informations about borrow date and return date, just add it to your array of "checkout" objects.

I will probably design it like this...

{
  "name":"david",
  "birthdate":"1971-12-26",
  "books":[
    {
      "title":"Star wars",
      "author":"Georges Lucas",
      "borrowdate":"2012-12-18",
      "returndate":null
    },
    {
      "title":"Star Trek",
      "author":"Whatever his name",
      "borrowdate":"2012-07-01",
      "returndate":"2012-08-15"
    }
  ]
}

Does it help?

David.

Answer 2

Create three types in your index, one for Books, one for User and one for a checkout. Store info about users and books using types "user" and "book" respectively. Every time a user checks out a book, store a document containing the user ID and book ID using type "checkout". Query the checkout type for all the books checked out by a user and all the users who checked out a book. Meanwhile, information for users and books is stored only once.