使用 postgres 构建一个触发器函数来处理 json 数据

Posted 2023-03-28

【中文标题】使用 postgres 构建一个触发器函数来处理 json 数据

【英文标题】：building a trigger function to process json data with postgres

【发布时间】：2016-01-14 15:51:22

【问题描述】：

我在构建 pl/pgsql 函数来处理 json 数组时遇到了困难。

我从客户端收到的数据是用户对问题的回答列表，我存储在我的表体验中一个名为“数据”的 json 类型字段中。

[
"completed":false,
"completed":false,
"completed":false,
"completed":true,"score":1,"answerList":["1"],"QuestionId":75,"startTime":"2016-01-09T16:40:06.153Z","clickNb":1,"endTime":"2016-01-09T16:40:07.844Z",
"completed":true,"score":1,"answerList":["1"],"QuestionId":76,"startTime":"2016-01-09T16:40:08.487Z","clickNb":1,"endTime":"2016-01-09T16:40:12.482Z",
"completed":true,"score":1,"answerList":["1"],"QuestionId":77,"startTime":"2016-01-09T16:40:13.042Z","clickNb":1,"endTime":"2016-01-09T16:40:17.689Z"
]

我想构建一个触发函数来将所有分数相加并将结果保存在一个名为 accuracy_score 的字段中。这是我到目前为止所构建的：

CREATE OR REPLACE FUNCTION calculate_accuracy() RETURNS TRIGGER AS $$
DECLARE 
    dataarray json;

BEGIN
    dataarray := json_array_elements(New.data);
    UPDATE experiences SET accuracy_score = subquery.score 
    FROM (SELECT SUM(dataarray->>'score') from dataarray) AS subquery 
    WHERE challenge_id = New.challenge_id;

    RETURN NULL;
END;
$$ LANGUAGE plpgsql;


CREATE TRIGGER calculate_accuracy
AFTER INSERT ON experiences
FOR EACH ROW EXECUTE PROCEDURE calculate_accuracy();

当我尝试运行它时收到以下错误消息：

错误：查询“SELECT json_array_elements(New.data)”返回多行 上下文：PL/pgSQL 函数 calculate_accuracy() 分配时的第 6 行

我不知道如何解决这个问题。在这方面提供更多的帮助！

【参考方案1】：

如果要更改插入行中的值，请使用 BEFORE TRIGGER 并在触发器函数中更改记录 NEW：

CREATE OR REPLACE FUNCTION calculate_accuracy() RETURNS TRIGGER AS $$
BEGIN
    NEW.accuracy_score = (
        SELECT sum((e->>'score')::int)
        FROM json_array_elements(NEW.data) e);
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER calculate_accuracy
BEFORE INSERT ON experiences
FOR EACH ROW EXECUTE PROCEDURE calculate_accuracy();

测试：

insert into experiences (challange_id, data)
values
(1, 
'[
"completed":false,
"completed":false,
"completed":false,
"completed":true,"score":1,"answerList":["1"],"QuestionId":75,"startTime":"2016-01-09T16:40:06.153Z","clickNb":1,"endTime":"2016-01-09T16:40:07.844Z",
"completed":true,"score":1,"answerList":["1"],"QuestionId":76,"startTime":"2016-01-09T16:40:08.487Z","clickNb":1,"endTime":"2016-01-09T16:40:12.482Z",
"completed":true,"score":1,"answerList":["1"],"QuestionId":77,"startTime":"2016-01-09T16:40:13.042Z","clickNb":1,"endTime":"2016-01-09T16:40:17.689Z"
]'::json)
returning challange_id, accuracy_score;

 challange_id | accuracy_score 
--------------+----------------
            1 |              3
(1 row)