返回 Postgres 嵌套 JSON 数组

Question

我一直在寻找这个问题的答案，但没有找到与我所寻找的足够接近的东西。

我有两张桌子：

CREATE TABLE skill_tree (
    ID SERIAL PRIMARY KEY,
    NAME TEXT NOT NULL,
    DESCRIPTION TEXT NOT NULL
);

和

CREATE TABLE skill (
    ID SERIAL PRIMARY KEY,
    NAME TEXT NOT NULL,
    DESCRIPTION TEXT NOT NULL,
    DURATION INTEGER NOT NULL,
    COOLDOWN INTEGER NOT NULL,
    SKILL_TREE_ID SERIAL REFERENCES skill_tree(id)
);

我正在尝试从我的 postgres 数据库返回 JSON，其结构如下：

[{
    "id": 1,
    "name": "skill tree 1",
    "description": "skill tree description",
    "skills": [{
        "id": 1,
        "name": "skill 1",
        "description": "skill 1 desc",
        "duration": 10,
        "cooldown": 20
    }, {
        "id": 2,
        "name": "skill 2",
        "description": "skill 2 desc",
        "duration": 20,
        "cooldown": 30
    }]
}]

我能够从这里 [PostgreSQL and nodejs/pg, return nested JSON 获得类似的东西，但除了技能名称之外无法检索到任何东西。

Answer 1

表格skill 应如下所示：

CREATE TABLE skill (
    ID SERIAL PRIMARY KEY,
    NAME TEXT NOT NULL,
    DESCRIPTION TEXT NOT NULL,
    DURATION INTEGER NOT NULL,
    COOLDOWN INTEGER NOT NULL,
    SKILL_TREE_ID INTEGER REFERENCES skill_tree(id) -- cannot be serial!
);

使用jsonb_build_object() 和jsonb_agg()。请注意，查询在某种程度上类似于预期的对象。

select jsonb_pretty(jsonb_agg(js_object)) result
from (
    select 
        jsonb_build_object(
            'id', id, 
            'name', name, 
            'description', description, 
            'skills', jsonb_agg(skill)
        ) js_object
    from (
        select 
            t.*, 
            jsonb_build_object(
                'id', s.id, 
                'name', s.name, 
                'description', s.description, 
                'duration', duration, 
                'cooldown', cooldown
            ) skill
        from skill_tree t
        join skill s on s.skill_tree_id = t.id
        ) s
    group by id, name, description
    ) s;

我已经用 jsonb_pretty() 包装了结果以获得一个不错的输出：

                     result                      
-------------------------------------------------
 [                                              +
     {                                          +
         "id": 1,                               +
         "name": "skill tree 1",                +
         "skills": [                            +
             {                                  +
                 "id": 1,                       +
                 "name": "skill 1",             +
                 "cooldown": 20,                +
                 "duration": 10,                +
                 "description": "skill 1 desc"  +
             },                                 +
             {                                  +
                 "id": 2,                       +
                 "name": "skill 2",             +
                 "cooldown": 30,                +
                 "duration": 30,                +
                 "description": "skill 2 desc"  +
             }                                  +
         ],                                     +
         "description": "skill tree description"+
     }                                          +
 ]

请注意，json 对象的元素顺序是不确定的。