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SpringBoot Entity中枚舉類型詳細(xì)使用介紹

更新時(shí)間：2022年10月20日 15:13:13 作者：IT利刃出鞘

本文介紹SpringBoot如何在Entity(DAO)中使用枚舉類型。(本文使用MyBatis-Plus）。在實(shí)際開發(fā)中，經(jīng)常會(huì)遇到表示類型或者狀態(tài)的情況，比如：有三種支付方式：微信、支付寶、銀聯(lián)。本文介紹如何這種場(chǎng)景的方案對(duì)比，并用實(shí)例來(lái)介紹如何用枚舉這種最優(yōu)雅的來(lái)表示

簡(jiǎn)介方案對(duì)比

本處列舉表示類型或狀態(tài)的常用方法的對(duì)比。

法1：使用數(shù)字表示（不推薦）

//1：支付寶支付；2：微信支付；3：銀行卡支付
private Integer payType;

這種方法的缺點(diǎn)：可讀性極差，排查問(wèn)題也麻煩。比如：前端頁(yè)面上看到了2這個(gè)類型，還要看接口文檔或者問(wèn)后端這是什么意思，浪費(fèi)時(shí)間！

法2：使用字符串表示（不推薦）

//ALIPAY：支付寶；WECHAT_PAY：微信；BANK_CARD_PAY：銀行卡支付
private String payType;

這種方式比法1好一些了，提高了數(shù)據(jù)庫(kù)的可讀性和排查問(wèn)題速度。

缺點(diǎn)：難以控制不允許數(shù)據(jù)庫(kù)的pay_type為空字符串這種情況；支持的類型沒(méi)有限制死，前端傳個(gè)其他的字符串也能存入數(shù)據(jù)庫(kù)。

法3：使用枚舉表示（推薦）

枚舉是這種場(chǎng)景最好的方案（枚舉本身就是為了表示可窮舉類型而發(fā)明出來(lái)的！）。

定義一個(gè)枚舉類

package com.example.demo.order.enums;
import lombok.Getter;
@Getter
public enum PayTypeEnum {
    ALIPAY("支付寶"),
    WECHAT_PAY("微信支付"),
    BANK_CARD_PAY("銀行卡支付"),
    ;
    private final String description;
    PayTypeEnum(String description) {
        this.description = description;
    }
}

Entity中定義枚舉類型字段

private PayTypeEnum payType;

優(yōu)點(diǎn)

可讀性極高，排查問(wèn)題很快（比如：前端頁(yè)面上看到ALIPAY這個(gè)類型，一眼就能知道是支付寶）
可以控制不允許數(shù)據(jù)庫(kù)的pay_type為空字符串這種情況（因?yàn)槊杜e字段不可能有空字符串）
支持的類型限制死，前端傳個(gè)其他的字符串無(wú)法存入數(shù)據(jù)庫(kù)。

枚舉用法示例

建表

CREATE TABLE `t_order` (
  `id` bigint NOT NULL COMMENT 'ID',
  `order_no` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '訂單號(hào)',
  `pay_type` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '支付類型。ALIPAY：支付寶；WECHAT_PAY：微信；BANK_CARD_PAY：銀行卡支付。',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='訂單';

pay_type字段加了NOT NULL限制。

Entity

package com.example.demo.order.entity;
import com.baomidou.mybatisplus.annotation.TableName;
import com.example.demo.order.enums.PayTypeEnum;
import lombok.Data;
@Data
@TableName("t_order")
public class Order {
    private Long id;
    private String orderNo;
    private PayTypeEnum payType;
}

Enum

package com.example.demo.order.enums;
import lombok.Getter;
@Getter
public enum PayTypeEnum {
    ALIPAY("支付寶"),
    WECHAT_PAY("微信支付"),
    BANK_CARD_PAY("銀行卡支付"),
    ;
    private final String description;
    PayTypeEnum(String description) {
        this.description = description;
    }
}

Controller

package com.example.demo.order.controller;
import com.example.demo.order.entity.Order;
import com.example.demo.order.service.OrderService;
import com.example.demo.user.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;
    @PostMapping("pay")
    public void pay(@RequestBody Order order) {
        orderService.save(order);
    }
}

Service

接口

package com.example.demo.order.service;
import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.order.entity.Order;
public interface OrderService extends IService<Order> {
}

實(shí)現(xiàn)

package com.example.demo.order.service.impl;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.order.entity.Order;
import com.example.demo.order.mapper.OrderMapper;
import com.example.demo.order.service.OrderService;
import org.springframework.stereotype.Service;
@Service
public class OrderServiceImpl extends ServiceImpl<OrderMapper, Order> implements OrderService {
}

Mapper

package com.example.demo.order.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.order.entity.Order;
import org.springframework.stereotype.Repository;
@Repository
public interface OrderMapper extends BaseMapper<Order> {
}

測(cè)試

1.正常操作

寫入成功，枚舉的name()方法的值會(huì)寫到數(shù)據(jù)庫(kù)。

后端結(jié)果

數(shù)據(jù)庫(kù)結(jié)果

2.前端傳空字符串

此時(shí)會(huì)報(bào)錯(cuò)，因?yàn)槊杜e中沒(méi)有對(duì)應(yīng)空字符串的。

后端結(jié)果（無(wú)法將空字符串反序列化為枚舉對(duì)象）

2022-09-10 10:14:30.406 WARN 128760 --- [nio-8080-exec-8] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `com.example.demo.order.enums.PayTypeEnum` from String "": not one of the values accepted for Enum class: [ALIPAY, BANK_CARD_PAY, WECHAT_PAY]; nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type `com.example.demo.order.enums.PayTypeEnum` from String "": not one of the values accepted for Enum class: [ALIPAY, BANK_CARD_PAY, WECHAT_PAY]
at [Source: (PushbackInputStream); line: 4, column: 16] (through reference chain: com.example.demo.order.entity.Order["payType"])]

數(shù)據(jù)庫(kù)結(jié)果（沒(méi)寫入數(shù)據(jù)）

3.前端傳null

后端結(jié)果（pay_type為null，寫入數(shù)據(jù)庫(kù)時(shí)報(bào)錯(cuò)）

2022-09-10 10:24:20.514 ERROR 128760 --- [io-8080-exec-10] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException:
### Error updating database. Cause: java.sql.SQLException: Field 'pay_type' doesn't have a default value
### The error may exist in com/example/demo/order/mapper/OrderMapper.java (best guess)
### The error may involve com.example.demo.order.mapper.OrderMapper.insert-Inline
### The error occurred while setting parameters
### SQL: INSERT INTO t_order ( id, order_no ) VALUES ( ?, ? )
### Cause: java.sql.SQLException: Field 'pay_type' doesn't have a default value
; Field 'pay_type' doesn't have a default value; nested exception is java.sql.SQLException: Field 'pay_type' doesn't have a default value] with root cause

java.sql.SQLException: Field 'pay_type' doesn't have a default value
   at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.zaxxer.hikari.pool.ProxyPreparedStatement.execute(ProxyPreparedStatement.java:44) ~[HikariCP-3.4.5.jar:na]
......

數(shù)據(jù)庫(kù)結(jié)果（沒(méi)寫入數(shù)據(jù)）