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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
SELECTuserId,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<String，Object>
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();@Overridepublic 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");}}@Overridepublic Map<String, Object> getResult(ResultSet rs, String columnName) throws SQLException {String json = rs.getString(columnName);return fromJson(json);}@Overridepublic Map<String, Object> getResult(ResultSet rs, int columnIndex) throws SQLException {String json = rs.getString(columnIndex);return fromJson(json);}@Overridepublic 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();@Overridepublic 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");}}@Overridepublic List<String> getResult(ResultSet rs, String columnName) throws SQLException {String json = rs.getString(columnName);return fromJson(json);}@Overridepublic List<String> getResult(ResultSet rs, int columnIndex) throws SQLException {String json = rs.getString(columnIndex);return fromJson(json);}@Overridepublic 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><if test="info != null">#{info,typeHandler=com.ruoyi.web.core.config.CustomJsonTypeHandler},</if></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><if test="tags != null">tags = #{tags,typeHandler=com.ruoyi.web.core.config.JsonArrayTypeHandler},</if></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><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