java - 当这些表的值没有更改时，为什么 hibernate 会执行冗余更新语句？

Question

我有以下代码:

public int makePayment(User forUser, Collection<Movie> cartItems, 
     Address deliverTo) 
{
   int returnCode = 0;

   LOGGER.debug("Number of items in cart - {}", cartItems.size());

   Rental rental = new Rental();
   rental.setRentalID(RandomStringUtils.randomAlphanumeric(ID_LENGTH).toUpperCase());
   rental.setUser(forUser); // Update reference to parent
   rental.setAddress(deliverTo);

   // Each rental has its own set of rented movies
   Set<RentedMovie> rentedMovies = new HashSet<>(cartItems.size());
   for (Iterator<Movie> iterator = cartItems.iterator(); iterator.hasNext();)
   {
      Movie movie = iterator.next();
      RentedMovie rentedMovie = new RentedMovie();
      rentedMovie.setMovie(movie);
      rentedMovie.setRental(rental); // Update reference to parent
      rentedMovies.add(rentedMovie);
   }

   rental.setRentedMovies(rentedMovies);
   rentalDAO.create(rental);

   Set<Rental> userRentals = userDAO.findById(forUser.getUserID()).getRentals();
   userRentals.add(rental); // Add to existing set of rentals

   try
   {
      String addressID = addressDAO.create(deliverTo);
      LOGGER.debug("Delivery Address successfully inserted. Generated address ID - {}", addressID);

      forUser.setRentals(userRentals);
      userDAO.update(forUser); // Internally calls session.merge()
   }
   catch (Exception e) {
      returnCode = -1;
      LOGGER.error("Exception during payment - {}", e.getMessage(), e);
   }

   return returnCode;
}

现在，当上述方法完成时，hibernate 会执行某些冗余更新查询，如下所述:

假设我向购物车添加了 2 件商品，所以...

DEBUG PaymentService - Number of items in cart - 2

接下来，在 RENTALS 表中插入一行(预期)

insert 
into
  rentals
  (bookingDate, userID, addressID, rentalID) 
values
  (?, ?, ?, ?)

USER 和 ADDRESS 表自在 RENTALS 中插入 1 行后更新一次(冗余)

update
  users 
set
  userName=?,
  password=?,
  firstName=?,
  lastName=?,
  email=?,
  addressID=? 
where
  userID=?

update
  addresses 
set
  line1=?,
  line2=?,
  city=?,
  state=?,
  pincode=? 
where
  addressID=?

MOVIES 表更新次数与购物车中的商品数量相同(本例中为 2 次，同样是多余的)

update
  movies 
set
  movieName=?,
  releaseYear=?,
  rating=?,
  nCopies=?,
  imageUri=?,
  plotLine=? 
where
  movieID=?

/* And another query with different movieID */

在 RENTED_MOVIE 表中插入 2 条记录(预期)

insert 
into
  rented_movie
  (rentalID, returnDate, movieID) 
values
  (?, ?, ?)

/* And one more with same rentalID and diff. movieID */

最后但并非最不重要的一点是，对 RENTALS 表进行选择查询(为什么？？)

上述冗余查询的原因是什么？

我正在使用 Hibernate 4.2.1 和 MySQL 5.5

<小时/>

链接到Schema Diagram

链接到User.hbm.xml

链接到Rental.hbm.xml

<小时/>

更新:似乎无论我尝试什么可能的逆组合，我似乎都无法避免这些n+2更新(n =购物车):(

有人可以告诉我这是否是已知行为吗？如果是，可能的解决方法是什么？

Answer 1

我终于解决了我的问题。问题在于级联设置。我已将其设置为 cascasde="all"在所有协会中。

我对 Rental.hbm.xml 进行了更改为关联设置特定级联选项:

<!-- n:1 mapping with User -->
<many-to-one name="user"
   column="userID"
   class="User"
   not-null="true"
   fetch="join"
   cascade="none" /> <!-- No cascading required for User -->

<!-- 1:1 mapping with Address. Association is MANDATORY. -->
<many-to-one name="address"
      column="addressID"
      class="Address"
      unique="true"
      not-null="true"
      cascade="persist"/> <!-- Either create a new delivery address or use an existing user address -->

<!-- m:n mapping with Movie -->
<set name="rentedMovies" table="rented_movie" lazy="true" 
    cascade="save-update, delete-orphan"> <!-- Selective update / delete -->
   <key column="rentalID"/>
   <composite-element class="RentedMovie">
      <parent name="rental"/>
      <property name="returnDate" column="returnDate" type="date" not-null="true"/>
      <many-to-one name="movie" column="movieID" class="Movie" not-null="true" fetch="join"/>
   </composite-element>
</set>

我从 <many-to-one name="movie" ../> 中删除了级联因为我通过传递 ID 列表来通过 HQL 更新库存计数，而不是更新对象本身的属性，因为后者会导致 N 个更新语句。