【golang-ent】go-zero框架 整合 ent orm框架 | 解决left join未关联报错的问题

一、场景

1、子表：cp_member_point_history

cp_member_point_history表中字段：cp_point_reward_id 是cp_point_reward的主键id
当本表中的cp_point_reward_id字段为0（即：没有可关联主表的）

CREATE TABLE `cp_member_point_history` (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `point` int DEFAULT NULL COMMENT '获取积分',
  `cp_point_reward_id` bigint DEFAULT NULL COMMENT '外键 cp_point_reward 主键id',
  `show_status` tinyint(1) DEFAULT NULL COMMENT '是否删除：0、可用，1:删除',
  `updated_at` datetime DEFAULT NULL COMMENT '更新时间',
  `created_at` datetime DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='用户积分变更历史';

2、主表：cp_point_reward

CREATE TABLE `cp_point_reward` (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `point` int DEFAULT NULL COMMENT '消耗积分',
  `name` varchar(255) COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '奖品名称',
  `reward` varchar(255) COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '奖品说明',
  `reward_status` int DEFAULT NULL COMMENT '1：上架、2：下架（默认是1）',
  `show_status` tinyint(1) DEFAULT NULL COMMENT '是否删除：0、可用，1:删除',
  `updated_at` datetime DEFAULT NULL COMMENT '更新时间',
  `created_at` datetime DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='积分奖品';

3、golang 使用 ent 源码

当 左连接 WithCpPointRewardMPH()时，无法进行关联时，则下面循环时，直接报错panic

package cpMemberPointHistory

import (
"context"
"fmt"
"github.com/suyuan32/simple-admin-common/utils/pointy"
"github.com/zeromicro/go-zero/core/logx"
)

type GetCpMemberPointHistoryListLogic struct {
ctx    context.Context
svcCtx *svc.ServiceContext
logx.Logger
}

func NewGetCpMemberPointHistoryListLogic(ctx context.Context, svcCtx *svc.ServiceContext) *GetCpMemberPointHistoryListLogic {
return &GetCpMemberPointHistoryListLogic{
ctx:    ctx,
svcCtx: svcCtx,
Logger: logx.WithContext(ctx),
}
}

func (l *GetCpMemberPointHistoryListLogic) GetCpMemberPointHistoryList(in *cpgobusiness.CpMemberPointHistoryListReq) (*cpgobusiness.CpMemberPointHistoryListResp, error) {
var predicates []predicate.CpMemberPointHistory
if in.CpMemberId != nil {
predicates = append(predicates, cpmemberpointhistory.CpMemberID(*in.CpMemberId))
}
if in.CpPointRewardId != nil {
predicates = append(predicates, cpmemberpointhistory.CpPointRewardID(*in.CpPointRewardId))
}
if in.CpResourceId != nil {
predicates = append(predicates, cpmemberpointhistory.CpResourceID(*in.CpResourceId))
}

result, err := l.svcCtx.DB.CpMemberPointHistory.Query().Where(predicates...).
WithCpMemberMPH().
WithCpPointRewardMPH().
WithCpResourceMPH().Page(l.ctx, in.Page, in.PageSize, func(pager *ent.CpMemberPointHistoryPager) {
pager.Order = ent.Desc(cpmemberpointhistory.FieldID)

})

if err != nil {
return nil, dberrorhandler.DefaultEntError(l.Logger, err, in)
}

resp := &cpgobusiness.CpMemberPointHistoryListResp{}
resp.Total = result.PageDetails.Total

for _, v := range result.List {
Template := &cpgobusiness.CpMemberPointHistoryInfo{
Id:              &v.ID,
CreatedAt:       pointy.GetPointer(v.CreatedAt.UnixMilli()),
UpdatedAt:       pointy.GetPointer(v.UpdatedAt.UnixMilli()),
ShowStatus:      pointy.GetPointer(int64(v.ShowStatus)),
CpMemberId:      &v.CpMemberID,
Point:           &v.Point,
ChangeType:      &v.ChangeType,
CpResourceId:    &v.CpResourceID,
CpPointRewardId: &v.CpPointRewardID,
GainType:        &v.GainType,
Name:            &v.Edges.CpMemberMPH.Name,
Phone:           &v.Edges.CpMemberMPH.Phone,
NickName:        &v.Edges.CpMemberMPH.NickName,
Gender:          &v.Edges.CpMemberMPH.Gender,
PointName:       pointy.GetPointer(""),
ResourceTitle:   &v.Edges.CpResourceMPH.Title,
}
if v.Edges.CpPointRewardMPH != nil {
fmt.Println("------------ v.Edges.CpPointRewardMPH.Name:", v.Edges.CpPointRewardMPH.Name)
Template.PointName = &v.Edges.CpPointRewardMPH.Name
}
resp.Data = append(resp.Data, Template)
}

return resp, nil
}

4、解决方案

问题：
报错的位置在：&v.Edges.CpPointRewardMPH.Name
因为 v.Edges.CpPointRewardMPH 为nil

解决

先判断 v.Edges.CpPointRewardMPH 是否为空
如果不为空，则赋值

if v.Edges.CpPointRewardMPH != nil {
fmt.Println("------------ v.Edges.CpPointRewardMPH.Name:", v.Edges.CpPointRewardMPH.Name)
Template.PointName = &v.Edges.CpPointRewardMPH.Name
}

原文地址：https://blog.csdn.net/wanglei19891210/article/details/140514839

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