Firestore：如何使用DocumentReference指向其他项目的文档？

Absolutely! You can use DocumentReference<T> to target documents in a different Firebase project, and it works smoothly since Firebase fully supports working with multiple projects in a single app.

Here’s a step-by-step breakdown of how to make this work:

• Initialize a secondary Firebase app instance
  First, set up a separate app instance for the target project. Pass the project’s unique configuration (apiKey, authDomain, projectId, etc.) and give the instance a distinct name to avoid conflicts with your default app:

  // Replace with your secondary project's actual config values
  const secondaryProjectConfig = {
    apiKey: "SECONDARY_PROJECT_API_KEY",
    authDomain: "secondary-project-id.firebaseapp.com",
    projectId: "secondary-project-id",
    // Include other required config fields like storageBucket, messagingSenderId, etc.
  };
  
  // Initialize the secondary app with a unique identifier
  const secondaryApp = firebase.initializeApp(secondaryProjectConfig, "secondary");
  

• Retrieve the Firestore instance for the secondary project
  Once the secondary app is initialized, grab its associated Firestore instance:

  const secondaryFirestore = secondaryApp.firestore();
  

• Create your cross-project DocumentReference
  Now you can generate a DocumentReference<T> exactly like you would for your primary project—this reference will point directly to a document in the secondary Firebase project:

  // Example: Reference a specific document in the secondary project's "posts" collection
  const crossProjectDocRef = secondaryFirestore.collection("posts").doc("summer-vacation-2024");
  

Key Considerations #

• Permissions are critical: Ensure the secondary project’s Firestore security rules allow your app to access the target documents. For backend code, you may need to use a service account with appropriate permissions for the secondary project.
• Clean up unused instances: If you no longer need the secondary app instance, call secondaryApp.delete() to free up resources and prevent memory leaks.
• Frontend checks: For web apps, confirm that the secondary project’s CORS settings don’t block requests from your primary app’s domain.

内容的提问来源于stack exchange，提问作者Alex