java巧用@Convert实现表字段自动转entity_Java

1.背景

本人自入职以来，接了一堆历史包(shi)袱(shan)，其中有个服务是基于mongodb实现的，而公司要搞信创化，去掉mongodb是迟早的事，于是便开始分析底层数据结构，计划用pg替换mongodb。

2.难点

2.1 数据结构不同

mongodb是文档型数据库，而pg是关系型数据库，原项目mongodb的collection中某些字段类型为list或者entity，存在一对多的情况，如果采用新建关联表的方式，会增加数据结构复杂性，且底层数据几乎不会变，因此，觉得直接用varchar类型存储list类型的json串。

2.2 数据类型转换

服务的数据库持久化使用的是jpa，原来mongodb类型会自动转成list，如下列的options属性

@data
@document(collection = "input_item")
public class inputitem implements comparable<inputitem> {

   @id
   private string itemcode;
   
   private string title;
   private string description;
   private int itemtype;
   private list<inputitemoption> options;
   private string defaultoptionnum;
   private string unit;
   private boolean whetheractive;
}

转成pg后，options字段在数据库中是string类型，需要转成list。经过调研，可以采用自定义converter+注解@convert来实现。

2.2.1 list类型

1）自定义converter

import com.alibaba.fastjson.json;
import javax.persistence.attributeconverter;
/**
 * @classname jpaconverterlistjson
 * @description jpa list转换为string 相互转换工具类
 * @author ygt
 * @date 2021/3/3 14:49
 * @version v1.0
 */
public class jpaconverterlistjson  implements attributeconverter<object, string> {
    @override
    public string converttodatabasecolumn(object o) {
        return json.tojsonstring(o);
    }

    @override
    public object converttoentityattribute(string s) {
        return json.parsearray(s);
    }
}

2）@convert注解

import java.util.list;
import com.fasterxml.jackson.annotation.jsoninclude;
import io.swagger.annotations.apimodel;
import lombok.allargsconstructor;
import lombok.builder;
import lombok.noargsconstructor;

import lombok.data;

import javax.persistence.*;

/**
 * 
 * @description 输入项实体类
 *
 */
@apimodel("")
@jsoninclude(value = jsoninclude.include.non_null)
@table(name = "input_item")
@builder
@allargsconstructor
@noargsconstructor
@data
@entity
public class inputitem implements comparable<inputitem> {

   @generatedvalue
   @column(name = "id")
   @id
   private string itemcode;

   @column(name = "title")
   private string title;
   @column(name = "description")
   private string description;
   @column(name = "itemtype")
   private int itemtype;

   @convert(converter = jpaconverterlistjson.class)
   private list<inputitemoption> options;
   @column(name = "defaultoptionnum")
   private string defaultoptionnum;
   @column(name = "unit")
   private string unit;
   @column(name = "whetheractive")
   private boolean whetheractive;

   @override
   public int compareto(inputitem o) {
      int index1 = integer.parseint(this.itemcode.substring(this.itemcode.lastindexof('_') + 1));
      int index2 = integer.parseint(o.itemcode.substring(o.itemcode.lastindexof('_') + 1));
      if (index1 < index2) {
         return -1;
      }
      else {
         return 1;
      }
   }
}

2.2.2 entity类型

1）自定义converter

import com.alibaba.fastjson.json;
import com.fasterxml.jackson.databind.objectmapper;
import com.test.src.domain.index.interest.interestcreditscoresection;

import javax.persistence.attributeconverter;
import java.lang.reflect.parameterizedtype;

/**
 * @classname jpaconverterlistjson
 * @description jpa 泛型t转换为string 相互转换工具类
 * @author ygt
 * @date 2021/3/3 14:49
 * @version v1.0
 */
public class jpaconverterobjectjson<t> implements attributeconverter<t, string> {

    private static final objectmapper objectmapper = new objectmapper();

    @override
    public string converttodatabasecolumn(t o) {
        try {
            return objectmapper.writevalueasstring(o);
        } catch (exception e) {
            throw new runtimeexception("failed to convert object to string", e);
        }
    }

    @override
    public t converttoentityattribute(string s) {
        try {
            return objectmapper.readvalue(s, (class<t>) ((parameterizedtype) getclass().getgenericsuperclass()).getactualtypearguments()[0]);
        } catch (exception e) {
            throw new runtimeexception("failed to convert string to object", e);
        }
    }
}

import com.test.src.domain.index.interest.interestcreditscoresection;

public class interestcreditscoresectionconverter extends jpaconverterobjectjson<interestcreditscoresection>{
}

2）@convert注解

import com.fasterxml.jackson.annotation.jsoninclude;
import com.test.src.utils.interestcreditscoresectionconverter;
import io.swagger.annotations.apimodel;
import lombok.noargsconstructor;

import lombok.*;

import javax.persistence.*;

/**
 * 
 * @description 利率授信实体类
 */
@apimodel("")
@jsoninclude(value = jsoninclude.include.non_null)
@table(name = "interest_credit")
@builder
@allargsconstructor
@noargsconstructor
@data
@entity
public class interestcredit {

   @id
   @generatedvalue
   @column(name = "id")
   private string itemno;

   @column(name = "recommendinterestformula")
   private string recommendinterestformula; //推荐执行利率计算公式;

   @convert(converter = interestcreditscoresectionconverter.class)
   @column(name = "interestcreditscoresection")
   private interestcreditscoresection interestcreditscoresection;
}