如何将对象添加到 Node-RED msg.payload答案

【问题标题】：How to add an object to the Node-RED msg.payload如何将对象添加到 Node-RED msg.payload
【发布时间】：2018-08-25 08:00:42
【问题描述】：

我需要 Accel 对象作为有效负载对象的一部分：

msg.payload.Accel.x：1
msg.payload.Accel.y : 2
msg.payload.Accel.z : 3

如何将 Accel 和 x,z,y 添加到有效负载，最好使用更改节点？

我已经试过了：

msg.payload.Accel['x'] = 1;
return msg;

得到一个错误：

"TypeError: Cannot set property 'x' of undefined"

【问题讨论】：

标签： node-red

【解决方案1】：

如果 payload 已经是一个对象，你可以使用 Change 节点在 payload 中添加或修改属性，如下所示：

[{"id":"a5a26aa9.8e0c48","type":"change","z":"b46a495a.46a938","name":"","rules":[{"t":"set","p":"payload.Accel.x","pt":"msg","to":"1","tot":"num"},{"t":"set","p":"payload.Accel.y","pt":"msg","to":"2","tot":"num"},{"t":"set","p":"payload.Accel.z","pt":"msg","to":"3","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":270,"y":260,"wires":[["85a0573d.ed8788","e0cc9521.5adb38"]]}]

如果有效负载以字符串（或其他非对象）的形式出现，并且您想使用 Change 节点将有效负载作为对象输出，则首先必须使用规则将 msg.payload 设置为空 JSON 对象，然后进一步规则将 msg.payload.Accel.x 设置为 1 等：

[{"id":"a5a26aa9.8e0c48","type":"change","z":"b46a495a.46a938","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"{}","tot":"json"},{"t":"set","p":"payload.Accel.x","pt":"msg","to":"1","tot":"num"},{"t":"set","p":"payload.Accel.y","pt":"msg","to":"2","tot":"num"},{"t":"set","p":"payload.Accel.z","pt":"msg","to":"3","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":270,"y":260,"wires":[["85a0573d.ed8788","e0cc9521.5adb38"]]}]

如果负载以字符串（或其他非对象）的形式出现，并且您希望使用 Change 节点将负载作为对象输出，并另外将旧负载内容保留为新负载对象的属性，那么您在将有效负载更改为对象之前，必须先使用规则将原始有效负载存储在临时变量中：

[{"id":"a5a26aa9.8e0c48","type":"change","z":"b46a495a.46a938","name":"","rules":[{"t":"set","p":"temp","pt":"msg","to":"payload","tot":"msg"},{"t":"set","p":"payload","pt":"msg","to":"{}","tot":"json"},{"t":"set","p":"payload.Accel.x","pt":"msg","to":"1","tot":"num"},{"t":"set","p":"payload.Accel.y","pt":"msg","to":"2","tot":"num"},{"t":"set","p":"payload.Accel.z","pt":"msg","to":"temp","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":270,"y":260,"wires":[["85a0573d.ed8788","e0cc9521.5adb38"]]}]

【讨论】：

【解决方案2】：

这完全取决于msg.payload 的开头。如果函数节点的输入是一个字符串，那么msg.payload 将是一个字符串，你不能只是给它添加任意属性。

如果输入已经是一个对象，那么它可以被扩展，但是你需要在对象中创建中间层才能添加值。例如假设以下输入msg.payload：

{
  foo: 25,
  bar: 'testing'
}

要添加Accel.x，您首先需要添加Accel 键，然后再尝试向Accel.x 添加值。使用功能节点，您可以这样做：

msg.payload.Accel = {};
msg.payload.Accel.x = 1;
msg.payload.Accel['y'] = 2;
return msg;

使用更改节点，它看起来像这样，因为更改节点将为您添加空层：

【讨论】：

如果负载以字符串形式出现，您仍然可以使用 Change 节点将其更改为对象。为此，从 Setmsg.payload 到 JSON{} 的规则开始，然后使用第二条规则设置 msg.payload.Accel.x 等。