spring data jpa 用法

1. Spring Data Jpa 关键字

动作关键字包括：get/find(查询)、delete(删除)、count(统计个数)，后面均可增加条件
如：

	// 根据姓名查找用户
	User findByName(String name);

	// 根据性别统计用户人数
	int countByGender(String gender);

	// 根据userId删除用户
    void deleteByUserId(Long userId);

关键字后可增加的条件

关键字	示例	同功能JPQL
And	findByLastnameAndFirstname	where x.lastname = ?1 and x.firstname = ?2
Or	findByLastnameOrFirstname	where x.lastname = ?1 or x.firstname = ?2
Is,Equals	findByFirstname,findByFirstnameIs,findByFirstnameEquals	where x.firstname = 1?
Between	findByStartDateBetween	where x.startDate between 1? and ?2
LessThan	findByAgeLessThan	where x.age < ?1
LessThanEqual	findByAgeLessThanEqual	where x.age <= ?1
GreaterThan	findByAgeGreaterThan	where x.age > ?1
GreaterThanEqual	findByAgeGreaterThanEqual	where x.age >= ?1
After	findByStartDateAfter	where x.startDate > ?1
Before	findByStartDateBefore	where x.startDate < ?1
IsNull	findByAgeIsNull	where x.age is null
IsNotNull,NotNull	findByAge(Is)NotNull	where x.age not null
Like	findByFirstnameLike	where x.firstname like ?1
NotLike	findByFirstnameNotLike	where x.firstname not like ?1
StartingWith	findByFirstnameStartingWith	where x.firstname like ?1 (参数后面加 %)
EndingWith	findByFirstnameEndingWith	where x.firstname like ?1 (参数前面加 %)
Containing	findByFirstnameContaining	where x.firstname like ?1 (参数两边加 %)
OrderBy	findByAgeOrderByLastnameDesc	where x.age = ?1 order by x.lastname desc
Not	findByLastnameNot	where x.lastname <> ?1
In	findByAgeIn(Collection ages)	where x.age in ?1
NotIn	findByAgeNotIn(Collection age)	where x.age not in ?1
True	findByActiveTrue()	where x.active = true
False	findByActiveFalse()	where x.active = false
IgnoreCase	findByFirstnameIgnoreCase	where UPPER(x.firstame) = UPPER(?1)