gorm 在加入 mysql 表后无法用数据填充嵌套结构

Question

在这里，我尝试加入 Branches_organization、orgnization 和 locations 这三个表，并将它们作为 API 响应发送。但是，organizationand location json 无法获取任何数据。

问题：

以下API响应无法检索组织和位置详细信息；总是返回零值

{
    "Title": "OK",
    "status": 200,
    "records": 1,
    "data": [
        {
            "branch_id": 51,
            "name": "my branch name",
            "address": "Mun",
            "telephone": "+9xxxxx",
            "organization": {
                "org_id": 0,
                "name": ""
            },
            "location": {
                "loc_id": 0,
                "name": ""
            }
        }
    ]
}

控制台错误

2022/08/17 06:11:32 /apiserver/controllers/handlers.go:3475 invalid field found for struct apiserver/entities.Custom_branches_organization's field Organization: define a valid foreign key for relations or implement the Valuer/Scanner interface
[7.930ms] [rows:1] SELECT branches_organization.branch_id,branches_organization.name,branches_organization.address,branches_organization.telephone,organization.org_id,organization.name,location.loc_id,location.name FROM `branches_organization` left join  organization on organization.org_id = branches_organization.org_id left join  location on location.loc_id =  branches_organization.loc_id

实施细节

使用的结构

用于 API 响应的结构

type Custom_branches_organization struct {
    Branch_id    uint         `json:"branch_id"`
    Name         string       `json:"name" validate:"required"`
    Address      string       `json:"address" validate:"required"`
    Telephone    string       `json:"telephone" validate:"e164,required"`
    Organization Organization `json:"organization" gorm:"foreignkey:org_id;references:Org_id"`
    Location     Location     `json:"location" gorm:"foreignkey:loc_id;references:Loc_id"`
}

子结构 //数据库中的组织表

type Organization struct {
    Org_id    uint   `json:"org_id"`
    Name      string `json:"name" validate:"required"`
    Address   string `json:"address"`
    Telephone string `json:"telephone" validate:"e164,required"`
    Email     string `json:"email" validate:"required,email"`
}

//数据库中的位置表

type Location struct {
    Loc_id    uint   `json:"loc_id"`
    Name      string `json:"name" validate:"required"`
    Address   string `json:"address" validate:"required"`
    Telephone string `json:"telephone" validate:"e164,required"`
}

//数据库中的实际分支表

type Branches_organization struct {
    Branch_id uint   `json:"branch_id"`
    Name      string `json:"name" validate:"required"`
    Address   string `json:"address" validate:"required"`
    Telephone string `json:"telephone" validate:"e164,required"`
    Org_id    uint   `json:"org_id" validate:"number"`
    Loc_id    uint   `json:"loc_id" validate:"number"`
}

Gorm 实施

//从branches_organization表中取出所有记录

var branches_organizations []entities.Custom_branches_organization

result := database.Instance.Model(&entities.Branches_organization{}).Preload("Organization").Preload("Location").Select("branches_organization.branch_id,branches_organization.name,branches_organization.address,branches_organization.telephone,organization.org_id,organization.name,location.loc_id,location.name").Joins("left join  organization on organization.org_id = branches_organization.org_id").Joins("left join  location on location.loc_id =  branches_organization.loc_id").Scan(&branches_organizations)

branches_organizationsdata := entities.Customebranches_organizationData{"OK", http.StatusOK, result.RowsAffected, branches_organizations}

json.NewEncoder(w).Encode(branches_organizationsdata)

数据库表

mysql> desc  organization;
+-----------+----------+------+-----+---------+----------------+
| Field     | Type     | Null | Key | Default | Extra          |
+-----------+----------+------+-----+---------+----------------+
| org_id    | int      | NO   | PRI | NULL    | auto_increment |
| name      | longtext | YES  |     | NULL    |                |
| address   | longtext | YES  |     | NULL    |                |
| telephone | longtext | YES  |     | NULL    |                |
| email     | longtext | YES  |     | NULL    |                |
+-----------+----------+------+-----+---------+----------------+
5 rows in set (0.12 sec)

mysql> desc  location;
+-----------+----------+------+-----+---------+----------------+
| Field     | Type     | Null | Key | Default | Extra          |
+-----------+----------+------+-----+---------+----------------+
| loc_id    | int      | NO   | PRI | NULL    | auto_increment |
| name      | longtext | YES  |     | NULL    |                |
| address   | longtext | YES  |     | NULL    |                |
| telephone | longtext | YES  |     | NULL    |                |
+-----------+----------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> desc branches_organization;
+-----------+----------+------+-----+---------+----------------+
| Field     | Type     | Null | Key | Default | Extra          |
+-----------+----------+------+-----+---------+----------------+
| branch_id | int      | NO   | PRI | NULL    | auto_increment |
| name      | longtext | YES  |     | NULL    |                |
| address   | longtext | YES  |     | NULL    |                |
| telephone | longtext | YES  |     | NULL    |                |
| org_id    | int      | YES  | MUL | NULL    |                |
| loc_id    | int      | YES  | MUL | NULL    |                |
+-----------+----------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

我花了很多天的时间来创建一个 json 回复，它将组织和位置详细信息作为嵌套结构。希望大家多多支持

Answer 1

你必须使用预加载来填充嵌套结构，类似于在 sql 查询中加入。请参考此文档。

https://gorm.io/docs/preload.html#nested_preloading

 type User struct {
  gorm.Model
  Username string
  Orders Order
}
type Order struct {
  gorm.Model
  UserID uint
  Price float64
}   
db.Preload("Username")
db.Preload("Orders").Find(&users)