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73 lines
3.0 KiB
Markdown
73 lines
3.0 KiB
Markdown
---
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title: Cloud Function Triggers
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---
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# {{ $frontmatter.title }}
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A trigger is a way to initiate the execution of a function. We can bind triggers to cloud functions to control when they are invoked.
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::: info
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Currently, triggers only support the scheduled trigger type.
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:::
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## Creating a Trigger
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Step 1: Click on the trigger button on the right side of the function list.
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Step 2: Create a new trigger.
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Step 3: Enter a name for the trigger for easy search and management in the future.
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Step 4: Select the type of trigger. Currently, only scheduled triggers are supported.
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Step 5: Choose the execution strategy for the scheduled task. Here, you can use cron expressions.
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If you are not familiar with `cron` expressions, you can click on the link below to choose from three preset options.
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Alternatively, you can click on the [More Examples](https://crontab.guru/examples.html) button to find the scheduled strategy you need or generate your own expression using the [Online Cron Expression](http://cron.ciding.cc/) website.
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## A specific example
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In the development process of WeChat Official Accounts, it is usually necessary to use a central control server to obtain and refresh the `access_token`. The `access_token` used by other business logic servers should all come from this central control server, and should not be refreshed individually. Otherwise, conflicts may occur, resulting in the access_token being overwritten and affecting the business.
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Generally, the validity period of the `access_token` is 2 hours, and this problem can be solved well using a scheduled trigger.
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1. First, let's create a cloud function named `get-access-token`.
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```typescript
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import cloud from '@lafjs/cloud'
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import axios from 'axios'
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const AT_BASEURL = 'https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential'
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const APP_ID = 'your appid'
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const APP_SECRET = 'your app secret'
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export async function main(ctx: FunctionContext) {
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try {
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const request_url = `${AT_BASEURL}&appid=${APP_ID}&secret=${APP_SECRET}`
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const { data: { access_token, expires_in, errcode, errmsg } } = await axios.get(request_url)
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if (errcode) return { errcode, errmsg }
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// write into cloud.shared
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cloud.shared.set('_access_token', access_token)
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cloud.shared.set('_expired_time', expires_in)
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} catch (error) {
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return {
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errcode: 500,
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err_msg: 'Get access token error: ' + error.toString() }
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}
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}
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```
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In the above code, we follow the [Interface Call Request Instructions](https://developers.weixin.qq.com/doc/offiaccount/Basic_Information/Get_access_token.html) in the WeChat official documentation to request the `access_token` and store it in `cloud.shared`. Other business functions can read it at any time.
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2. Use a trigger
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Do you remember the process of creating a trigger just now? We only need to select the associated function as `get-access-token` and set the Cron expression to 2 hours to request the WeChat API every two hours to refresh the `access_token` to ensure validity. |