mybatis动态sql-注解方式-05
05-mybatis动态sql-注解方式
基于注解方式实现动态sql
动态sql除了支持xml方式以外，还是支持使用纯注解的方式
主要一下四个注解+对应动态sql语句的类文件
-
@InsertProvider 动态查询SQL语句对应注解
-
@InsertProvider 动态插入SQL语句对应注解
-
@UpdateProvider 动态修改SQL语句对应注解
-
@DeleteProvider 动态删除SQL语句对应注解
允许构建动态 SQL。这些备选的 SQL 注解允许你指定返回 SQL 语句的类和方法，以供运行时执行。（从 MyBatis 3.4.6 开始，可以使用 CharSequence 代替 String 来作为返回类型）。当执行映射语句时，MyBatis 会实例化注解指定的类，并调用注解指定的方法。你可以通过 ProviderContext 传递映射方法接收到的参数、“Mapper interface type” 和 “Mapper method”（仅在 MyBatis 3.4.5 以上支持）作为参数。（MyBatis 3.4 以上支持传入多个参数）属性：type、method。type 属性用于指定类名。method 用于指定该类的方法名（从版本 3.5.1 开始，可以省略 method 属性，MyBatis 将会使用 ProviderMethodResolver 接口解析方法的具体实现。如果解析失败，MyBatis 将会使用名为 provideSql 的降级实现）。提示 接下来的“SQL 语句构建器”一章将会讨论该话题，以帮助你以更清晰、更便于阅读的方式构建动态 SQL。
问题
Java 程序员面对的最痛苦的事情之一就是在 Java 代码中嵌入 SQL 语句。这通常是因为需要动态生成 SQL 语句，不然我们可以将它们放到外部文件或者存储过程中。如你所见，MyBatis 在 XML 映射中具备强大的 SQL 动态生成能力。但有时，我们还是需要在 Java 代码里构建 SQL 语句。此时，MyBatis 有另外一个特性可以帮到你，让你从处理典型问题中解放出来，比如加号、引号、换行、格式化问题、嵌入条件的逗号管理及 AND 连接。确实，在 Java 代码中动态生成 SQL 代码真的就是一场噩梦
解决方案
MyBatis 3 提供了方便的工具类来帮助解决此问题。借助 SQL 类，我们只需要简单地创建一个实例，并调用它的方法即可生成 SQL 语句。
看面案例:
需求1:通过条件查询
查询姓名带黄的或者 age = 25
Mapper接口:
/*
* @SelectProvider(type=UserSqlBuilder.class,method="selectByCondition")
* @SelectProvider 查询动态sql语句的 注解
* type ： 编写动态sql语句的类对应的字节码
* method ： 编写动态sql语句类对应的方法名称
* 此方法返回的是一个String字符串，字符串就是拼接sql语句
*/
@SelectProvider(type = UserSqlBuilder.class,method = "selectByCondition")
List selectByCondition(User user);
UserSqlBuilder sql构建类:
public class UserSqlBuilder {
public String selectByCondition(User user){
// 创建 sql 对象 构建 sql字符串
SQL sql = new SQL();
// select *
sql.SELECT("*");
// select * from t_user
sql.FROM("t_user");
// select * from t_user where name like #{name}
if (user.getName() != null) {
sql.WHERE("name like #{name}");
}
//默认多条件是AND ，可以自己制定成 OR
if (user.getAge() != null) {
sql.OR();
sql.WHERE("age = #{age}");
}
return sql.toString();
}
}
测试代码sql的构建:
@Test
public void testSelectConditionSQLBuilder(){
UserSqlBuilder userSqlBuilder = new UserSqlBuilder();
User u = new User();
u.setName("%黄%");
u.setAge(25);
String s = userSqlBuilder.selectByCondition(u);
System.out.println(s);
}
查看日志:
SELECT *
FROM t_user
WHERE (name like #{name})
OR (age = #{age})
测试代码:
@Test
public void testSelectCondition(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapperAnnotation mapper = sqlSession.getMapper(UserMapperAnnotation.class);
User u = new User();
u.setName("%黄%");
u.setAge(25);
List users = mapper.selectByCondition(u);
System.out.println(users);
SqlSessionUtils.close(sqlSession);
}
日志:
DEBUG [main] - ==> Preparing: SELECT * FROM t_user WHERE (name like ?) OR (age = ?)
DEBUG [main] - ==> Parameters: %黄%(String), 25(Integer)
TRACE [main] - <== Columns: id, name, pwd, age
TRACE [main] - <== Row: 4, 洪七公, aaa, 25
TRACE [main] - <== Row: 5, 黄蓉, 阿里巴巴, 38
TRACE [main] - <== Row: 6, 王语嫣, abc, 25
TRACE [main] - <== Row: 7, 周芷若, 1234, 25
TRACE [main] - <== Row: 8, 黄药师, 1234, 66
DEBUG [main] - <== Total: 5
需求2:通过条件查询统计结果
Mapper接口:
Long selectTotalByCondition(User user);
UserSqlBuilder sql构建类:
public String selectTotalByCondition(User user){
SQL sql = new SQL();
// select *
sql.SELECT("count(*) ");
// select * from t_user
sql.FROM("t_user");
// select * from t_user where name like name = #{name}
if (user.getName() != null) {
sql.WHERE(" name like name = #{name}");
}
if (user.getAge() != null) {
// select * from t_user where name like name = #{name} or age = #{age}
sql.OR();
sql.WHERE("age = #{age}");
}
return sql.toString();
}
测试sql构建:
@Test
public void testselectTotalByConditionSqlBuilder() {
UserSqlBuilder sqlBuilder = new UserSqlBuilder();
User u = new User();
u.setName("%黄%");
u.setAge(25);
String s = sqlBuilder.selectTotalByCondition(u);
System.out.println(s);
}
日志:
SELECT count(*)
FROM t_user
WHERE ( name like name = #{name})
OR (age = #{age})
测试代码:
@Test
public void testSelectTotalByCondition(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapperAnnotation mapper = sqlSession.getMapper(UserMapperAnnotation.class);
User u = new User();
u.setName("%黄%");
u.setAge(25);
Long aLong = mapper.selectTotalByCondition(u);
System.out.println(aLong);
SqlSessionUtils.close(sqlSession);
}
日志:
DEBUG [main] - ==> Preparing: SELECT count(*) FROM t_user WHERE ( name like name = ?) OR (age = ?)
DEBUG [main] - ==> Parameters: %黄%(String), 25(Integer)
TRACE [main] - <== Columns: count(*)
TRACE [main] - <== Row: 3
DEBUG [main] - <== Total: 1
3
需求3:修改用户
mapper接口:
@UpdateProvider(type = UserSqlBuilder.class, method = "updateUserByNotNull")
int updateUserByNotNull(User user);
UserSqlBuilder sql构建类:
public String updateUserByNotNull(User user){
SQL sql = new SQL();
// update t_user
sql.UPDATE("t_user");
// update t_user set name = #{name}
if (user.getName() != null) { // 不要自己在后面加 ,
sql.SET("name = #{name}");
}
// update t_user set name = #{name},age = #{age}
if (user.getAge() != null) {
sql.SET("age = #{age}");
}
// update t_user set name = #{name},age = #{age},pwd = #{pwd}
if (user.getPwd() != null) {
sql.SET("pwd = #{pwd}");
}
// update t_user set name = #{name},age = #{age},pwd = #{pwd} where id = #{id}
sql.WHERE("id = #{id}");
return sql.toString();
}
sql构建的测试：
@Test
public void testUpdateSqlBuilder() {
UserSqlBuilder sqlBuilder = new UserSqlBuilder();
User u = new User();
u.setName("紫衫龙王");
u.setAge(25);
u.setId(4);
String s = sqlBuilder.updateUserByNotNull(u);
System.out.println(s);
}
日志:
UPDATE t_user
SET name = #{name}, age = #{age}
WHERE (id = #{id})
测试代码:
@Test
public void testUpdate(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapperAnnotation mapper = sqlSession.getMapper(UserMapperAnnotation.class);
User u = new User();
u.setName("紫衫龙王");
u.setAge(25);
u.setId(8);
int i= mapper.updateUserByNotNull(u);
sqlSession.commit();
System.out.println(i);
SqlSessionUtils.close(sqlSession);
}
日志:
DEBUG [main] - ==> Preparing: UPDATE t_user SET name = ?, age = ? WHERE (id = ?)
DEBUG [main] - ==> Parameters: 紫衫龙王(String), 25(Integer), 8(Integer)
DEBUG [main] - <== Updates: 1
1
需求4:通过多个id删除数据
mapper的代码:
@DeleteProvider(type = UserSqlBuilder.class,method = "deleteUsers")
int deleteUsers(@Param("list") List list);
UserSqlBuilder sql构建类:
public String deleteUsers(@Param("list") List list){
SQL sql = new SQL();
// delete from t_user
sql.DELETE_FROM("t_user");
// 没有拼接的方法 只能自己写字符串拼接
// 拼接条件 (#{list[0]},#{list[1]},#{list[2]})
StringBuilder sb = new StringBuilder();
sb.append("(");
for (int i = 0; i < list.size(); i++) {
sb.append("#{list["+i+"]},");
}
// 删除 字符串拼接最后一个 ,
sb.deleteCharAt(sb.length() - 1);
sb.append(")");
// delete from t_user where id in (1,2,3);
sql.WHERE("id in " +sb.toString());
return sql.toString();
}
sql测试代码:
@Test
public void testDeleteSqlBuilder() {
UserSqlBuilder sqlBuilder = new UserSqlBuilder();
List list =new ArrayList<>();
list.add(1);
list.add(4);
list.add(5);
sqlBuilder.deleteUsers(list);
String s = sqlBuilder.deleteUsers(list);
System.out.println(s);
}
日志:
DELETE FROM t_user
WHERE (id in (#{list[0]},#{list[1]},#{list[2]}))
测试代码:
@Test
public void testSelectList(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List list =new ArrayList<>();
list.add(1);
list.add(4);
list.add(5);
List users = mapper.selectList(list);
System.out.println(users);
SqlSessionUtils.close(sqlSession);
}
日志:
DEBUG [main] - ==> Preparing: DELETE FROM t_user WHERE (id in (?,?,?))
DEBUG [main] - ==> Parameters: 1(Integer), 4(Integer), 5(Integer)
DEBUG [main] - <== Updates: 3
3
需求5:批量插入
mapper接口:
@InsertProvider(type = UserSqlBuilder.class,method = "insertUsers")
int insertUsers(@Param("users")List list);
UserSqlBuilder sql构建类:
public String insertUsers(@Param("users")List list){
SQL sql = new SQL();
// insert into t_user(name,pwd,age) values (?,?,?)
StringBuilder sb = new StringBuilder();
sb.append("insert into t_user(name,pwd,age) values ");
for (int i = 0; i < list.size(); i++) {
sb.append("(");
sb.append("#{users["+i+"].name},");
sb.append("#{users["+i+"].pwd},");
sb.append("#{users["+i+"].age}");
sb.append("),");
}
sb.deleteCharAt(sb.length() - 1);
return sb.toString();
}
sql构建测试代码:
@Test
public void testInsertSqlBuilder() {
UserSqlBuilder sqlBuilder = new UserSqlBuilder();
List list =new ArrayList<>();
list.add(new User(null,"梅超风","123",30));
list.add(new User(null,"曲正风","123",40));
list.add(new User(null,"空见","123",35));
String s = sqlBuilder.insertUsers(list);
System.out.println(s);
}
测试代码:
@Test
public void testInsertUsers(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapperAnnotation mapper = sqlSession.getMapper(UserMapperAnnotation.class);
List list =new ArrayList<>();
list.add(new User(null,"梅超风","123",30));
list.add(new User(null,"曲正风","123",40));
list.add(new User(null,"空见","123",35));
mapper.insertUsers(list);
sqlSession.commit();
SqlSessionUtils.close(sqlSession);
}
日志:
DEBUG [main] - ==> Preparing: insert into t_user(name,pwd,age) values (?,?,?),(?,?,?),(?,?,?)
DEBUG [main] - ==> Parameters: 梅超风(String), 123(String), 30(Integer), 曲正风(String), 123(String), 40(Integer), 空见(String), 123(String), 35(Integer)
DEBUG [main] - <== Updates: 3