使用 jsonb_agg/jsonb_build_object 解析为内部结构

Question

每当我尝试获取 (select/scan) 组（外部结构）及其协作者（内部结构）时，我都会收到以下错误： // sql: Scan error on column index ..., name "collaborators": unsupported Scan, storing driver.Value type []uint8 into type *[]User

我正在使用 sqlx（带有 pgx 驱动程序）。

从数据库获取的代码是：

func (psql *Postgres) GetGroups(someParam string) ([]Group, error) {
   groups := []Group{}
   err := psql.db.Unsafe().Select(&groups, <the query ...>, someParam)
   ....
}

type Postgres struct {
    db      *sqlx.DB
    config  *config.PostgresDB
    timeout time.Duration
}

这是 SQL 查询：

SELECT groups.id, 
       groups.title,
       JSONB_AGG(JSONB_BUILD_OBJECT(
        'id', u.id,
        'first_name', u.first_name, 
        'last_name', u.last_name,
        'user_pic_url', u.user_pic_url)) as collaborators
FROM groups
JOIN user_group_permissions p
ON   p.group_id = groups.id
JOIN users u
ON   u.id = p.user_id

这些是结构：

type Group struct {
    Id             string  `json:"id" db:"id"`
    Title          string  `json:"title"   db:"title"`
    Collaborators  []User  `json:"collaborators" db:"collaborators"`
}

type User struct {
    Id            string  `json:"id" db:"id"`
    FirstName     string  `json:"first_name" db:"first_name"`
    LastName      string  `json:"last_name" db:"last_name"`
    ProfilePhoto  *string `json:"profile_photo" db:"user_pic_url"`
}

我有一个简单的组 table ，一个用户 table 和 table 代表对该组具有权限的所有用户：

CREATE TABLE groups (
   id    int UNIQUE NOT NULL generated always as identity,
   title text
)

CREATE TABLE users (
    id       bigint UNIQUE NOT NULL generated always as identity,
    first_name   text NOT NULL,
    last_name    text NOT NULL,
    user_pic_url text
)

CREATE TABLE user_group_permissions (
   group_id   unsigned_int,
   user_id    unsigned_bigint,
   permission unsigned_smallint,
)


CREATE DOMAIN unsigned_smallint AS smallint
   CHECK(VALUE >= 0 AND VALUE < 32767);

CREATE DOMAIN unsigned_int AS int
   CHECK(VALUE >= 0 AND VALUE < 2147483647);

CREATE DOMAIN unsigned_bigint AS bigint
   CHECK(VALUE >= 0 AND VALUE < 9223372036854775807);

Answer 1

import "encoding/json"

type Group struct {
    Id             string   `json:"id" db:"id"`
    Title          string   `json:"title"   db:"title"`
    Collaborators  UserList `json:"collaborators" db:"collaborators"`
}

type User struct {
    Id            string  `json:"id" db:"id"`
    FirstName     string  `json:"first_name" db:"first_name"`
    LastName      string  `json:"last_name" db:"last_name"`
    ProfilePhoto  *string `json:"profile_photo" db:"user_pic_url"`
}

type UserList []User

func (list *UserList) Scan(src interface{}) error {
    var data []byte
    switch v := src.(type) {
    case []byte:
        data = v
    case string:
        data = []byte(v)
    default:
        return nil // or return some error
    }
    return json.Unmarshal(data, list)
}

使用 jsonb_agg/jsonb_build_object 解析为内部结构

Using jsonb_agg/jsonb_build_object to parse to inner structs

sql

postgresql

go

sqlx

pgx