LoopBack中before save钩子无法通过ctx访问外部模型与请求对象

I've run into similar issues with LoopBack 3's operation hooks before, so here are practical fixes for your problems:

1. Get Request Object, URL, HTTP Method, and User ID #

The default operation hook context (ctx) doesn't include the request object directly, but you can pass it through using a beforeRemote hook or use the loopback-context module.

Option 1: Pass Request via beforeRemote Hook (Most Reliable) #

This method attaches the request to the hook's options, making it accessible in any subsequent operation hooks:

module.exports = function (Org) {
  // Attach req to all remote method options
  Org.beforeRemote('**', function(ctx, _, next) {
    ctx.options.req = ctx.req;
    next();
  });

  // Access request data in your operation hook (e.g., access hook)
  Org.observe('access', function(ctx, next) {
    const req = ctx.options.req;
    if (req) {
      const url = req.originalUrl;
      const httpMethod = req.method;
      // Get userId if your API uses LoopBack's default authentication
      const userId = req.accessToken?.userId;

      console.log('Request URL:', url);
      console.log('HTTP Method:', httpMethod);
      console.log('Authenticated User ID:', userId);
    }
    next();
  });
};

Option 2: Use loopback-context for Global Access #

If you prefer a global approach, install the loopback-context module first:

npm install loopback-context

Then add the middleware to server/middleware.json:

"initial": {
  "loopback-context#per-request": {}
}

Now you can fetch the request in your operation hook:

const LoopBackContext = require('loopback-context');

module.exports = function (Org) {
  Org.observe('access', function(ctx, next) {
    const currentCtx = LoopBackContext.getCurrentContext();
    if (currentCtx) {
      const req = currentCtx.get('req');
      const url = req.originalUrl;
      const httpMethod = req.method;
      const userId = req.accessToken?.userId;

      // Use the data as needed
    }
    next();
  });
};

Note: This can have context loss issues with async operations, so the beforeRemote method is generally safer.

2. Access External Models #

You don't need ctx to access other models—use the Org model's app property to fetch any registered model:

module.exports = function (Org) {
  Org.observe('access', async function(ctx, next) {
    // Fetch an external model (e.g., User)
    const User = Org.app.models.User;
    
    // Example: Fetch a user using the userId from the request
    const req = ctx.options.req;
    if (req?.accessToken?.userId) {
      const user = await User.findById(req.accessToken.userId);
      console.log('Fetched User:', user);
    }
    next();
  });
};

Just make sure the external model is registered in server/model-config.json—this works for any model you've set up in your LoopBack app.

Quick Notes #

• This assumes you're using LoopBack 3 (your code syntax matches it). For LoopBack 4, the approach is different.
• To get userId, ensure your API has authentication enabled (using LoopBack's built-in AccessToken model or a third-party auth component).
• Different operation hooks (e.g., before save, after delete) will have slightly different ctx structures, but options is consistently available to pass custom data.

内容的提问来源于stack exchange，提问作者Gary