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Book Copy Model Migration

Problem Solved

The old model had a significant issue: books had a quantity field that showed how many copies existed, but when someone borrowed a book, there was no way to know which specific copy was borrowed. This created problems when returning books.

Solution

A new BookCopy model was created that represents each physical copy of a book:

New Entities

  • BookCopy: Each physical copy of a book
  • Book: No longer has a quantity field, but has a relationship with BookCopy
  • Borrow: Now connects to BookCopy instead of Book

Key Changes

  1. Book Model:

    • Removed the quantity field
    • Added OneToMany relationship with BookCopy
    • Added calculated methods: getTotalCopies(), getAvailableCopies()

  2. BookCopy Model:

    • copyId: Unique ID for each copy
    • book: Relationship with the book
    • copyNumber: Copy number (1, 2, 3, etc.)
    • isAvailable: Whether it's available for borrowing
    • condition: Condition of the copy

  3. Borrow Model:

    • Now connects to BookCopy instead of Book
    • The BorrowId uses bookCopyId instead of bookId

New API Endpoints

BookCopy Management

  • GET /api/book-copies/book/{bookId} - All copies of a book
  • GET /api/book-copies/book/{bookId}/available - Available copies
  • GET /api/book-copies/book/{bookId}/available/count - Number of available copies
  • POST /api/book-copies/book/{bookId}/add/{quantity} - Add copies
  • PUT /api/book-copies/{copyId} - Update copy
  • DELETE /api/book-copies/{copyId} - Delete copy

Migration Endpoints

  • POST /api/migration/create-default-copies - Create default copies
  • POST /api/migration/migrate-quantities - Migration from old model

How to Migrate

Step 1: Database Schema Update

You need to create the BOOK_COPIES table:

CREATE TABLE BOOK_COPIES (
    COPY_ID BIGINT AUTO_INCREMENT PRIMARY KEY,
    BOOK_ID BIGINT NOT NULL,
    COPY_NUMBER INTEGER NOT NULL,
    IS_AVAILABLE BOOLEAN NOT NULL DEFAULT TRUE,
    CONDITION VARCHAR(50),
    FOREIGN KEY (BOOK_ID) REFERENCES BOOKS(BOOK_ID)
);

Step 2: Update BORROWS table

-- Add new column
ALTER TABLE BORROWS ADD COLUMN BOOK_COPY_ID BIGINT;

-- You'll need to migrate existing borrow data manually
-- This is complex and depends on your existing data

Step 3: Run Migration

Call the endpoint:

POST /api/migration/create-default-copies

This will create a default copy for each book that doesn't have copies.

Step 4: Clean up (Optional)

After migration, you can remove the QUANTITY column from the BOOKS table:

ALTER TABLE BOOKS DROP COLUMN QUANTITY;

Advantages of the New Model

  1. Precise tracking: Each copy has its own ID
  2. Better management: You can track the condition of each copy
  3. Return problem solution: You know exactly which copy is being returned
  4. Extensibility: You can add more information for each copy

Important Notes

  • The API for borrow/return remains the same (uses bookId)
  • The logic automatically finds an available copy for borrowing
  • For returns, it finds the correct copy that the user borrowed
  • The BookDTO still has a quantity field that is calculated from the copies