[英]How to make a mysql “ladder” queries in nodejs with express
我有一个问题,当我想用nodejs,express和mysql以“阶梯”形式进行查询并返回一个json时,它对我不起作用,我要制作的结构是:
select dev_id*,dev_name from devices
select cont_id*, cont_name from controllers where dev_id = dev_id
select act_id, acti_id from actions where cont_id = cont_id**
return json({devices,{controller,{actions}}})
我正在使用forEach函数,也尝试使用回调函数。
您需要连接所有3个表,然后遍历结果并构建嵌套对象。
var mysql = require("mysql");
var con = mysql.createConnection({
host: "localhost",
user: "yourusername",
password: "yourpassword",
database: "mydb"
});
var sql = `SELECT d.dev_id, d.dev_name, c.cont_id, c.cont_name, a.act_id, a.acti_id
FROM devices AS d
LEFT JOIN controllers AS c ON c.dev_id = c.dev_id
LEFT JOIN actions AS a ON a.cont_id = c.cont_id`;
con.connect(err => {
if (err) {
throw err;
}
conn.query(sql, (err, result, fields) => {
if (err) {
throw err;
}
var devices = {};
$result.forEach(({dev_id, dev_name, cont_id, cont_name, act_id, acti_id}) => {
devices[dev_id] = devices[dev_id] || {id: dev_id, name: dev_name, controllers: {}};
devices[dev_id].controllers[cont_id] = devices[dev_id].controllers[cont_id] || {id: cont_id, name: cont_name, actions: {}};
devices[dev_id].controllers[cont_id].actions[act_id] = {id: act_id, acti_id: acti_id};
});
});
// do something with devices here
});
请记住,所有的mysql查询代码都是异步的,因此您不能正常返回值。 您需要使用回调或Promise。
devices
变量将如下所示:
{
devid1: {
id: "devid1",
name: "devname1",
controllers: {
contid1: {
id: "contid1",
name: "contname1",
actions: {
actionid1: {
id: "actionid1",
acti_id: "acti_id1"
},
actionid2: {
id: "actionid2",
acti_id: "acti_id2"
}
}
},
contid2: {
id: "contid2",
name: "contname2",
actions: {
actionid3: {
id: "actionid3",
acti_id: "acti_id3"
}
}
}
|
}
}
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