Java Mybatis 接收postgreSQL中array_agg的结果

Posted 2023-03-08 洛阳泰山

问题描述

因为项目中业务需求，postgreSQL使用了group by与array_agg将varchar或者bigint类型变为一个数组，这样多行结果就变为了一行结果，但是mybatis的jdbcType没有对应的数据类型。如果用string类型去接收，还得用java代码处理成数组，返回给前端有点麻烦。

array_agg介绍

array_agg函数 和string_agg 函数类似，最主要的区别为返回的类型为数组，数组数据类型同输入数据类型一致，array_agg函数支持两种语法。

解决

方式一：

通过设置mybatis xml配置和创建自定义数据类型处理类解决。

教程

maper类 以mybatis-plus常规分页写法示例

import java.util.List;

import com.baomidou.mybatisplus.core.metadata.IPage;
import org.springblade.standardmodel.mineupdown.dto.AdvancedDetectionTunnelDTO;
import org.springblade.standardmodel.mineupdown.entity.AdvancedDetection;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;

public interface AdvancedDetectionMapper extends BaseMapper<AdvancedDetection> 

    List<AdvancedDetectionTunnelDTO> tunnelPage(IPage page, String tunnelName);

mapper.xml文件中设置typeHander

    <resultMap id="BaseResultMap" type="org.springblade.standardmodel.mineupdown.dto.AdvancedDetectionTunnelDTO">
        <result column="ids" jdbcType="ARRAY" property="ids" typeHandler="org.springblade.standardmodel.common.handler.ArrayTypeHandler"/>
    </resultMap>

    <select id="tunnelPage" resultMap="BaseResultMap">
            SELECT
            ids,
            tunnel_id,
            tunnel_name,
            anomalous_region_num
            FROM
            (
            SELECT
            "array_agg" ( ID ) ids,
            tunnel_id,
            tunnel_name,
            "sum" ( anomalous_region_num ) anomalous_region_num
            FROM
            (
            SELECT
            ad.ID,
            ad.tunnel_id,
            tb.hd_hdmc AS tunnel_name,
            ( SELECT COUNT ( 1 ) FROM gis_standard_abnormal_area aa WHERE aa.detection_id = ad.ID ) AS anomalous_region_num
            FROM
            gis_standard_advanced_detection ad
            LEFT JOIN gis_standard_tunnel_base tb ON ad.tunnel_id = tb.ID
            ) T
            GROUP BY
            T.tunnel_id,
            T.tunnel_name
            ) r
         <where>
             <if test="tunnelName!=null">
                 and r.tunnel_name like CONCAT('%',#tunnelName,'%')
             </if>
         </where>
    </select>

自定义数组类型处理类 ArrayTypeHandler

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import org.apache.ibatis.type.TypeException;

import java.sql.*;

public class ArrayTypeHandler extends BaseTypeHandler<Object[]> 

    private static final String TYPE_NAME_VARCHAR = "varchar";
    private static final String TYPE_NAME_INTEGER = "integer";
    private static final String TYPE_NAME_BOOLEAN = "boolean";
    private static final String TYPE_NAME_NUMERIC = "numeric";

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, Object[] parameter, JdbcType jdbcType) throws SQLException 
        String typeName = null;
        if (parameter instanceof Integer[]) 
            typeName = TYPE_NAME_INTEGER;
         else if (parameter instanceof String[]) 
            typeName = TYPE_NAME_VARCHAR;
         else if (parameter instanceof Boolean[]) 
            typeName = TYPE_NAME_BOOLEAN;
         else if (parameter instanceof Double[]) 
            typeName = TYPE_NAME_NUMERIC;
        

        if (typeName == null) 
            throw new TypeException("ArrayTypeHandler parameter typeName error, your type is " + parameter.getClass().getName());
        

        Connection conn = ps.getConnection();
        Array array = conn.createArrayOf(typeName, parameter);
        ps.setArray(i, array);
    

    @Override
    public Object[] getNullableResult(ResultSet resultSet, String s) throws SQLException 
        return getArray(resultSet.getArray(s));
    

    @Override
    public Object[] getNullableResult(ResultSet resultSet, int i) throws SQLException 
        return getArray(resultSet.getArray(i));
    

    @Override
    public Object[] getNullableResult(CallableStatement callableStatement, int i) throws SQLException 
        return getArray(callableStatement.getArray(i));
    

    private Object[] getArray(Array array) 
        if (array == null) 
            return null;
        
        try 
            return (Object[]) array.getArray();
         catch (Exception e) 
        
        return null;
    

实体类返回对象AdvancedDetectionTunnelDTO

import io.swagger.annotations.ApiModelProperty;
import lombok.Data;


/**
 * @author TARZAN
 */
@Data
public class AdvancedDetectionTunnelDTO 


    @ApiModelProperty("巷道名称")
    private  String tunnelName;

    @ApiModelProperty("异常区域数")
    private  Integer anomalousRegionNum;

    @ApiModelProperty("超前探id集合")
    private Long[] ids;

方式二：

通过 mybatis-plus @TableField(typeHandler = ArrayTypeHandler.class) 注解

实体类返回对象AdvancedDetectionTunnelDTO

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableName;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.experimental.Accessors;
import org.apache.ibatis.type.ArrayTypeHandler;



/**
 * @author TARZAN
 */
@Data
@Accessors(chain = true)
@TableName(autoResultMap = true)
public class AdvancedDetectionTunnelDTO 


    @ApiModelProperty("巷道名称")
    private  String tunnelName;

    @ApiModelProperty("异常区域数")
    private  Integer anomalousRegionNum;

    @ApiModelProperty("超前探id集合")
    @TableField(typeHandler = ArrayTypeHandler.class)
    private Long[] ids;

注意事项：

需要用到两个注解才能生效

1. @TableName(autoResultMap = true)

2. @TableField(typeHandler = ArrayTypeHandler.class)