目录（1）一对一，@OneToOne（2）一对多，@OneToMany 和 @ManyToOne（3）多对多，@ManyToMany自从接触了JPA，就对立面的级联操作很费解，特此做一下学习。JPA提供的Entity级联可以建立一对一、一对多、多对多的关系，
Windows Forms\' CheckBox control implements both CheckedChanged and CheckStateChanged events. As far as I can tell, both fire when the checked status of the checkbox is changed.
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