hibernate load 方法与get方法

1.get()采用立即加载方式,而load()采用延迟加载;
               get()方法执行的时候,会立即向数据库发出查询语句,
               而load()方法返回的是一个代理(此代理中只有一个id属性),只有等真正使用该对象属性的时候,才会发出sql语句
             2.如果数据库中没有对应的记录,get()方法返回的是null.而load()方法出现异常ObjectNotFoundException

1. session.get()

For example, in a Stock application , Stock and StockTransactions should have a “one-to-many” relationship, when you want to save a stock transaction, it’s common to declared something like below。

Stock stock = (Stock)session.get(Stock.class, new Integer(2));
StockTransaction stockTransactions = new StockTransaction();
//set stockTransactions detail
stockTransactions.setStock(stock);       
session.save(stockTransactions);

Output:
Hibernate:
    select ... from mkyong.stock stock0_
    where stock0_.STOCK_ID=?
Hibernate:
    insert into mkyong.stock_transaction (...)
    values (?, ?, ?, ?, ?, ?)


In session.get() hibernate will hit the database retrieve the Stock object and put it as a reference to StockTransaction.
我仅仅需要一个引用而已 并不需要所有的属性
After all you just need the Stock’s Id as a reference to StockTransaction.

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所以有session.load()
2.session.load()

Stock stock = (Stock)session.load(Stock.class, new Integer(2));
StockTransaction stockTransactions = new StockTransaction();
//set stockTransactions detail
stockTransactions.setStock(stock);       
session.save(stockTransactions);

Output:
Hibernate:
       insert into stock_transaction (...)
       values (?, ?, ?, ?, ?, ?)

In session.load(), Hibernate will not hit the database (no select statement in output) to retrieve the Stock object, it will return a Stock proxy object – a fake object with given identify value. In this scenario, a proxy object is enough for to save a stock transaction record