Comprehensive analysis of MyBatis tags: analyze the role and usage of each tag in MyBatis one by one

# This mybatis tag Full analysis: Analyze the role and usage of each label in mybatis one by one, you need to specify the code for example

1. ain ## MyBatis is an excellent long -lasting framework. It supports custom SQL statements and mapping relationships, providing some important labels to realize interaction with the database. In this article, we will analyze the role and usage of each tag in MyBatis one by one, and provide corresponding code examples.

SQL statement tag

2. 2.1. select

select tag is used to define query statements. The following is an example:

<select id="getUserById" resultType="User">
    SELECT * FROM users WHERE id = #{id}
</select>

2.2. insert

insert tag is used to define insert statements. The following is an example:

<insert id="insertUser" parameterType="User">
    INSERT INTO users (id, name, age) VALUES (#{id}, #{name}, #{age})
</insert>

2.3. update

The update tag is used to define update statements. The following is an example:

<update id="updateUser" parameterType="User">
    UPDATE users SET name = #{name}, age = #{age} WHERE id = #{id}
</update>

2.4. delete

delete tag is used to define delete statements. The following is an example:

<delete id="deleteUser" parameterType="int">
    DELETE FROM users WHERE id = #{id}
</delete>

Parameter transfer tag

3. 3.1. parameterMap

The parameterMap tag is used to define parameter mapping relationships. The following is an example:

<parameterMap id="userMap" type="User">
    <parameter property="id" jdbcType="INTEGER"/>
    <parameter property="name" jdbcType="VARCHAR"/>
    <parameter property="age" jdbcType="INTEGER"/>
</parameterMap>

3.2. parameterType

The parameterType tag is used to specify the parameter type. The following is an example:

<select id="getUserById" resultType="User">
    SELECT * FROM users WHERE id = #{id}
</select>

Result set mapping tag

4. 4.1. resultMap

resultMap tag is used to define the result set mapping relationship. The following is an example:

<resultMap id="userResultMap" type="User">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="age" column="age"/>
</resultMap>

4.2. result

result tag is used to define field mapping relationships. The following is an example:

<resultMap id="userResultMap" type="User">
    <result property="id" column="id"/>
</resultMap>

Dynamic SQL tag

5. 5.1. if

The if tag is used to dynamically generate the conditional part of the SQL statement. The following is an example:

<select id="getUserByName" resultType="User">
    SELECT * FROM users
    <where>
        <if test="name != null">
            AND name = #{name}
        </if>
        <if test="age != null">
            AND age = #{age}
        </if>
    </where>
</select>

5.2. choose, when, otherwise

choose, when, otherwise tags are used for multiple conditional judgments. The following is an example:

<select id="getUserByCondition" resultType="User">
    SELECT * FROM users
    <where>
        <choose>
            <when test="name != null">
                AND name = #{name}
            </when>
            <when test="age != null">
                AND age = #{age}
            </when>
            <otherwise>
                AND gender = #{gender}
            </otherwise>
        </choose>
    </where>
</select>

and above is the introduction and usage of some commonly used tags in MyBatis. I believe that through the understanding and application of these tags, you can better use MyBatis for database operations. At the same time, we provide corresponding code examples, hoping to help you better understand and apply the MyBatis framework.

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