mybatis查询修改mysql的json字段

前言：

mysql5.7版本之后支持json字段类型，推荐mysql8版本，适用于属性不确定的个性化字段，比如:
身份信息{“职业”,“学生”,“兴趣”:“打乒乓球”,“特长”:“跳高，书法”};
图片信息{“日期”:“2023-12-12 22:12”,“尺寸”:“215*720”,“拍摄地”:“xxx”,“作者”:“xxx”};
标签信息：[“历史”,“军事”,“都市”,“科幻”]。
这部分信息每条数据差异较大，固定字段会大量冗余，使用json有较高的扩展性和自由度

JSON对象除了支持字符串、整型、日期类型，JSON 内嵌的字段也支持数组类型

sql语句中对json的新增和查询

新增

CREATE TABLE UserLogin (
    userId BIGINT NOT NULL,
    loginInfo JSON,
    PRIMARY KEY(userId)
);
SET @a = '
{
   "cellphone" : "1",
   "wxchat" : "码农",
   "77" : "1"
}';
INSERT INTO UserLogin VALUES (1,@a);

查询

字段回显

SELECT
    userId,
    JSON_UNQUOTE(JSON_EXTRACT(loginInfo,"$.cellphone")) cellphone,
    JSON_UNQUOTE(JSON_EXTRACT(loginInfo,"$.wxchat")) wxchat
FROM UserLogin;
等效于

SELECT 
    userId,
    loginInfo->>"$.cellphone" cellphone,
    loginInfo->>"$.wxchat" wxchat
FROM UserLogin;

条件筛选

CREATE TABLE `photos ` (
  `id` bigint NOT NULL COMMENT '文件在云端的唯一标识ID',
  `tags` json DEFAULT NULL COMMENT '标签数组',
  `info` json DEFAULT NULL COMMENT '照片生成信息json',
  PRIMARY KEY (`id`) USING BTREE
);

-- json字段属性筛选，查询拍摄地是重庆的
SELECT * FROM photos WHERE JSON_EXTRACT(info, '$.拍摄地') = '重庆';

-- 查询标签包含10的图片
SELECT * FROM photos WHERE 10 MEMBER OF(tags->"$");

-- 查询标签包含2和10的图片
SELECT * FROM photos WHERE JSON_CONTAINS(tags->"$", '[2,10]');
-- 或者
SELECT * FROM photos WHERE JSON_OVERLAPS(tags->"$", '[2,10]');

JSON_CONTAINS 返回json数组是否包含指定的数组
JSON_OVERLAPS 返回json数组是否与指定的数组有交集

建立索引

相当于增加虚拟列

-- 为json中的手机号建立索引
ALTER TABLE UserLogin ADD COLUMN cellphone VARCHAR(255) AS (loginInfo->>"$.cellphone");
ALTER TABLE UserLogin ADD UNIQUE INDEX idx_cellphone(cellphone);

-- 也可以在建表时创建索引

CREATE TABLE UserLogin (
    userId BIGINT,
    loginInfo JSON,
    cellphone VARCHAR(255) AS (loginInfo->>"$.cellphone"),
    PRIMARY KEY(userId),
    UNIQUE KEY uk_idx_cellphone(cellphone)
);

-- 使用索引的虚拟列查询
SELECT  *  FROM UserLogin WHERE cellphone = '11'

mybatis自定义转换

mysql与java实体常见的字段映射不需要我们特别指定，json字段因为其灵活性，需要单独指定。
我这里列举出上例中photos表的json与java实体的map和list的转换，
如果你的java实体中json字段映射的其他类型直接在示例转换上修改类型即可。
（也可以用泛型写通用转换）

json == > Map

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Map;

public class CustomJsonTypeHandler implements TypeHandler<Map<String, Object>> {

    private static final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public void setParameter(PreparedStatement ps, int i, Map<String, Object> parameter, JdbcType jdbcType) throws SQLException {
        try {
            String json = objectMapper.writeValueAsString(parameter);
            ps.setString(i, json);
        } catch (JsonProcessingException e) {
            throw new SQLException("Error converting Map to JSON");
        }
    }

    @Override
    public Map<String, Object> getResult(ResultSet rs, String columnName) throws SQLException {
        String json = rs.getString(columnName);
        return fromJson(json);
    }

    @Override
    public Map<String, Object> getResult(ResultSet rs, int columnIndex) throws SQLException {
        String json = rs.getString(columnIndex);
        return fromJson(json);
    }

    @Override
    public Map<String, Object> getResult(CallableStatement cs, int columnIndex) throws SQLException {
        String json = cs.getString(columnIndex);
        return fromJson(json);
    }

    private Map<String, Object> fromJson(String json) throws SQLException {
        if (json == null || json.isEmpty()) {
            return null;
        }
        try {
            return objectMapper.readValue(json, Map.class);
        } catch (JsonProcessingException e) {
            throw new SQLException("Error converting JSON to Map");
        }
    }
}

json == > List

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeHandler;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;

public class JsonArrayTypeHandler implements TypeHandler<List<String>> {

    private static final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public void setParameter(PreparedStatement ps, int i, List<String> parameter, JdbcType jdbcType) throws SQLException {
        try {
            String json = objectMapper.writeValueAsString(parameter);
            ps.setString(i, json);
        } catch (JsonProcessingException e) {
            throw new SQLException("Error converting Integer[] to JSON");
        }
    }

    @Override
    public List<String> getResult(ResultSet rs, String columnName) throws SQLException {
        String json = rs.getString(columnName);
        return fromJson(json);
    }

    @Override
    public List<String> getResult(ResultSet rs, int columnIndex) throws SQLException {
        String json = rs.getString(columnIndex);
        return fromJson(json);
    }

    @Override
    public List<String> getResult(CallableStatement cs, int columnIndex) throws SQLException {
        String json = cs.getString(columnIndex);
        return fromJson(json);
    }

    private List<String> fromJson(String json) throws SQLException {
        if (json == null || json.isEmpty()) {
            return null;
        }
        try {
            return objectMapper.readValue(json, List.class);
        } catch (JsonProcessingException e) {
            throw new SQLException("Error converting JSON to Integer[]");
        }
    }
}

mapper.xml中的输入与输出

输入

	-- 新增信息
  	<insert id="insertPhotos" parameterType="Photos">
        insert into photos
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="tags != null">tags,</if>
            <if test="info != null">info,</if>
        </trim>
        <trim prefix="values (" suffix=")" suffixOverrides=",">
            <if test="tags != null">#{tags, typeHandler=com.ruoyi.web.core.config.JsonArrayTypeHandler},
            <if test="info != null">#{info,typeHandler=com.ruoyi.web.core.config.CustomJsonTypeHandler},
        </trim>
    </insert>

	-- 修改信息
    <update id="updatePhotos" parameterType="Photos">
        update photos
        <trim prefix="SET" suffixOverrides=",">
            <if test="info  != null">info = #{info,typeHandler=com.ruoyi.web.core.config.CustomJsonTypeHandler},
            <if test="tags != null">tags = #{tags,typeHandler=com.ruoyi.web.core.config.JsonArrayTypeHandler},
        </trim>
        where id= #{id}
    </update>

输出

    <resultMap type="Photos" id="PhotosResult">
        <result property="id" column="id"/>
        <result property="tags" column="tags" javaType="java.util.List" typeHandler="com.ruoyi.web.core.config.JsonArrayTypeHandler"/>
        <result property="info" column="tags" javaType="java.util.List" typeHandler="com.ruoyi.web.core.config.CustomJsonTypeHandler"/>
    </resultMap>

    <select id="PhotosList" parameterType="Photos" resultMap="PhotosResult">
        <include refid="selectPhotosVo"/>
        <where>
            <if test="id != null ">and id = #{id}
            <if test="tags != null ">
                and JSON_CONTAINS(tags->"$",
                #{tags, typeHandler=com.ruoyi.web.core.config.JsonArrayTypeHandler}
                )
            </if>
        </where>
    </select>

部分json查询语法参考文章：https://mp.weixin.qq.com/s?src=11×tamp=1706855643&ver=5055&signature=xH0-aTP0U1liqYAzXaSvvqAqto5UUiPrJY5P1-qizaGNTpmSTV7ZY7qkqyMujiUWM8dhenWhjDLecMoMgeXBwMYffwSSbLKe2UrQ308ZaDBUaVJ4ku29U0X05XZh&new=1