@Setter
@Getter
@Entity
public class User {
    @Id
    @GenericGenerator(name="jpauuid",strategy = "org.hibernate.id.UUIDGenerator")
    @GeneratedValue(generator = "jpauuid")
    @Column(length = 32,nullable = false)
    private String  id;
    @Column(length = 30)
    private String username;
    @ManyToMany(cascade = CascadeType.REFRESH,mappedBy = "users")
    private Set<Role> roles;
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return id.equals(user.id) &&
                username.equals(user.username) &&
                roles.equals(user.roles);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id, username, roles);
    }
    @Override
    public String toString() {
        return "User{" +
                "id='" + id + '\'' +
                ", username='" + username + '\'' +
                ", roles=" + roles +
                '}';
    }
}

@Setter
@Getter
@Entity
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;
    @Column(length = 30)
    private String  name;
    @ManyToMany(cascade = CascadeType.REFRESH)
    @JoinTable(name = "user_role",joinColumns = @JoinColumn(name = "role_id"),inverseJoinColumns = @JoinColumn(name="user_id"))
    private Set<User>  users;
}

 deleteInBatch(Iterable<T> entities) 
/**
  點(diǎn)進(jìn)源碼 看看。
  org.springframework.data.jpa.repository.support.SimpleJpaRepository#deleteInBatch
*/
	@Transactional
	public void deleteInBatch(Iterable<T> entities) { 
		Assert.notNull(entities, "The given Iterable of entities not be null!"); 
		if (!entities.iterator().hasNext()) {
			return;
		} 
// 繼續(xù)跟蹤
		applyAndBind(getQueryString(DELETE_ALL_QUERY_STRING, entityInformation.getEntityName()), entities, em)
				.executeUpdate();
	}  
/**
 org.springframework.data.jpa.repository.query.QueryUtils#applyAndBind
*/ 
public static <T> Query applyAndBind(String queryString, Iterable<T> entities, EntityManager entityManager) {
   // ... 省略一些code
   // 最后會(huì)形成 delete from xx表  x(表別名) where x.id =? or x.id=?... 一條sql語(yǔ)句 
        String alias = detectAlias(queryString);
		StringBuilder builder = new StringBuilder(queryString);
		builder.append(" where"); 
		int i = 0; 
		while (iterator.hasNext()) { 
			iterator.next(); 
			builder.append(String.format(" %s = ?%d", alias, ++i)); 
			if (iterator.hasNext()) {
				builder.append(" or");
			}
		}
 
		Query query = entityManager.createQuery(builder.toString()); 
		iterator = entities.iterator();
		i = 0; 
		while (iterator.hasNext()) {
			query.setParameter(++i, iterator.next());
		}  
}