【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

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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）

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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

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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

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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 cpMemberPointHistoryimport ("context""fmt""github.com/suyuan32/simple-admin-common/utils/pointy""github.com/zeromicro/go-zero/core/logx"
)type GetCpMemberPointHistoryListLogic struct {ctx    context.ContextsvcCtx *svc.ServiceContextlogx.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.CpMemberPointHistoryif 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.Totalfor _, 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
}