@Indexed
public interface Repository<T, ID> {}

@NoRepositoryBean
public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> {<S extends T> S save(S var1); //保存<S extends T> Iterable<S> save(Iterable<S> var1);//批量保存T findOne(ID var1);//根据id 查询一个对象。返回对象本身，当对象不存在时，返回nullboolean exists(ID var1)//根据id 判断对象是否存在Iterable<T> findAll();;//查询所有的对象Iterable<T> findAllById(Iterable<ID> var1);//根据id列表查询所有的对象long count();//计算对象的总个数void delete(ID var1);//根据id 删除void delete(T var1);//删除一个对象void delete(Iterable<? extends T> var1);//批量删除，集合对象（后台执行时，一条一条删除）void deleteAll();//删除所有（后台执行时，一条一条删除）
}

@NoRepositoryBean
public interface PagingAndSortingRepository<T, ID extends Serializable> extends CrudRepository<T, ID> {Iterable<T> findAll(Sort var1);// 仅排序Page<T> findAll(Pageable var1);// 分页和排序
}

@NoRepositoryBean
public interface JpaRepository<T, ID extends Serializable> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {List<T> findAll(); //查询所有对象，返回ListList<T> findAll(Sort var1);//查询所有对象，并排序，返回ListList<T> findAll(Iterable<ID> var1);//根据id列表查询所有的对象，返回List<S extends T> List<S> save(Iterable<S> var1);//批量保存，并返回对象Listvoid flush();//强制缓存与数据库同步<S extends T> S saveAndFlush(S var1);//保存并强制同步数据库void deleteInBatch(Iterable<T> var1);//批量删除集合对象（后台执行时，生成一条语句执行，用多个or条件）void deleteAllInBatch();//删除所有（执行一条语句，如：delete from user）T getOne(ID var1);//根据id 查询一个对象，返回对象的引用（区别于findOne），当对象不存时，返回引用不是null，但各个属性值是null<S extends T> List<S> findAll(Example<S> var1);//根据实例查询<S extends T> List<S> findAll(Example<S> var1, Sort var2);//根据实例查询，并排序
}

/*** Interface to allow execution of {@link Specification}s based on the JPA criteria API.*/
public interface JpaSpecificationExecutor<T> {T findOne(Specification<T> var1); //通过Specification查询单个对象List<T> findAll(Specification<T> var1); //通过Specification查询集合Page<T> findAll(Specification<T> var1, Pageable var2); //通过Specification分页查询List<T> findAll(Specification<T> var1, Sort var2); //通过Specification排序查询long count(Specification<T> var1);//通过Specification统计
}

public interface UserRepository extends JpaRepository<User, Long> {//这种"?1"占位符要求和参数位置对应，推荐使用别名//nativeQuery=true说明为原生SQL//@Query(value = "SELECT * FROM USERS WHERE EMAIL_ADDRESS = ?1", nativeQuery = true)@Query(value = "SELECT * FROM USERS WHERE EMAIL_ADDRESS = :emailAddress", nativeQuery = true)User findByEmailAddress(String emailAddress);//delete、update example@Modifying@Query("update User u set u.firstname = :firstname where u.lastname = :lastname")int setFixedFirstnameFor(String firstname, String lastname);@Modifying@Query("delete from User u where user.role.id = :roleId")void deleteInBulkByRoleId(long roleId);
}

Page<DemoUser> result = userRepository.findAll(new Specification<DemoUser>(){@Overridepublic Predicate toPredicate(Root<DemoUser> root, CriteriaQuery<?> query, CriteriaBuilder builder) {List<Predicate> predicates = new ArrayList<>();//关联查询 innerJoin<DemoUser, DemoDept> join = root.join("demoDept", JoinType.INNER);//主表条件 like 动态条件if (StringUtils.isNotBlank(demoUserDtoQueryDto.getUserName())) {predicates.add(builder.like(root.get("userName"), //属性"%" + demoUserDtoQueryDto.getUserName() + "%")); //值}//in使用测试CriteriaBuilder.In<Long> in = builder.in(root.get("id"));Arrays.asList(1L, 2L, 3L).forEach(e -> {in.value(e);});predicates.add(in);//从表条件 id=1predicates.add(builder.equal(join.get("id"), 1)); //从表条件查询 这里测试//or使用 (password=4 or sex=1)predicates.add(builder.or(builder.equal(root.get("password"), "44"),builder.equal(root.get("sex"), "1")));//对象类型比较要求比较器//<Y extends Comparable<? super Y>> Predicate greaterThanOrEqualTo(Expression<? extends Y> x, Expression<? extends Y> y);//   builder.greaterThanOrEqualTo();//   builder.lessThanOrEqualTo();//   builder.greaterThan();//   builder.lessThan();//直接用与数值类型的值进行比较//Predicate gt(Expression<? extends Number> x, Expression<? extends Number> y);//   builder.gt();//   builder.le();return builder.and(predicates.toArray(new Predicate[predicates.size()]));//    query.where(predicates.toArray(new Predicate[predicates.size()]));//    return null;}},new PageRequest(page, pageSize); //分页参数 还可以添加排序字段
);// ---------------------------------------------------------------------------------------
// Entity
@Entity
@Table(name = "demo_user")
@Data
public class DemoUser extends BaseDomain implements Serializable {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Long id;private String userName;private String password;private Short sex;@ManyToOne@JoinColumn(name = "dept_id")@NotFound(action = NotFoundAction.IGNORE)private DemoDept demoDept;}// ---------------------------------------------------------------------------------------
// DAO
public interface UserRepository extends JpaRepository<DemoUser, Long>, JpaSpecificationExecutor<DemoUser> {}