java之mybatis语法

1、增加（Insert）：

xml
<insert id="insertUser" parameterType="User">
  INSERT INTO user (id, name, age) VALUES (#{id}, #{name}, #{age})
</insert>
对应Java代码：

java
sqlSession.insert("insertUser", user);
sqlSession.commit();

2、删除（Delete）：

xml
<delete id="deleteUserById" parameterType="int">
  DELETE FROM user WHERE id = #{id}
</delete>
对应Java代码：

java
sqlSession.delete("deleteUserById", userId);
sqlSession.commit();

3、修改（Update）：

xml
<update id="updateUser" parameterType="User">
  UPDATE user SET name = #{name}, age = #{age} WHERE id = #{id}
</update>
对应Java代码：

java
sqlSession.update("updateUser", user);
sqlSession.commit();

4、查询（Select）：

xml
<select id="getUserById" parameterType="int" resultType="User">
  SELECT * FROM user WHERE id = #{id}
</select>
对应Java代码：

java
User user = sqlSession.selectOne("getUserById", userId);

在MyBatis中，可以使用动态SQL来构建灵活的增删改查语句，以应对不同的查询条件和业务需求。以下是一些常见的动态SQL语法示例：

5、动态条件查询：

xml
<select id="getUserByCondition" parameterType="Map" resultType="User">
  SELECT * FROM user
  <where>
    <if test="name != null">
      AND name = #{name}
    </if>
    <if test="age != null">
      AND age = #{age}
    </if>
  </where>
</select>
对应Java代码：

java
Map<String, Object> params = new HashMap<>();
params.put("name", "John");
List<User> users = sqlSession.selectList("getUserByCondition", params);

6、动态插入：

xml
<insert id="insertUser" parameterType="User">
  INSERT INTO user
  <trim prefix="(" suffix=")" suffixOverrides=",">
    <if test="name != null">name,</if>
    <if test="age != null">age,</if>
  </trim>
  <trim prefix="values (" suffix=")" suffixOverrides=",">
    <if test="name != null">#{name},</if>
    <if test="age != null">#{age},</if>
  </trim>
</insert>
对应Java代码：

java
User user = new User("Alice", 25);
sqlSession.insert("insertUser", user);
sqlSession.commit();

7、 动态更新：

xml
<update id="updateUser" parameterType="User">
  UPDATE user
  <set>
    <if test="name != null">name = #{name},</if>
    <if test="age != null">age = #{age},</if>
  </set>
  WHERE id = #{id}
</update>
对应Java代码：

java
User user = new User(1, "Bob", 30);
sqlSession.update("updateUser", user);
sqlSession.commit();

8、动态删除：

xml
<delete id="deleteUserByCondition" parameterType="Map">
  DELETE FROM user
  <where>
    <if test="name != null">AND name = #{name}</if>
    <if test="age != null">AND age = #{age}</if>
  </where>
</delete>
对应Java代码：

java
Map<String, Object> params = new HashMap<>();
params.put("name", "Tom");
sqlSession.delete("deleteUserByCondition", params);
sqlSession.commit();