Saving Data on Android

GeTng started
To see how the security rules look like open your Firestore database in the console. 
You'll see 
Rules
 tab at the top. Click on it. Then click on the 
Simulator
 icon to 
expand the simulator window:
This is where you can see your current logic for the security rules.
You'll take a deeper look into these rules next.
match /databases/{database}/documents
This line indicates the path that all the documents belong to. By default, all the 
documents belong to the 
/databases/{database}/documents
 path.
match /{document=**} { 
      ... 
}
This is where you set the rules for the specific document by specifying the path to
Saving Data on Android
Chapter 19: Securing Data in Cloud Firestore
raywenderlich.com
275

---

that document. 
match
 statement specifies the path to the document. 
document=**
 is 
a recursive wildcard which matches any document in the entire database. As of May 
2019, there is version 2 of the Cloud Firestore security rules which changes the 
behavior of the recursive wildcards. Check the official documentation 
https://
firebase.google.com/docs/firestore/security/get-started#security_rules_version_2
 to 
see the differences in the behavior.
In your current database, you have a posts collection that contains a specific post. 
The path to the specific post looks like this:
/databases/{database}/documents/posts/{postId}
If you only want to write a security rule that applies to that specific path you'd do it 
like this:
match /databases/{database}/documents { 
    match posts/{postId} { 
      ... 
    } 
}
As you can see, Firestore lets you nest the paths.
The first 
match
 you see will almost always look like this:
match /databases/{database}/documents
{database}
 in curly brackets is a wildcard that matches any database name. You'll 
learn more about wildcards later.
Now, your 
posts
 collection could have a subcollection. You could add a separate rule 
for that subcollection like this:
match /databases/{database}/documents { 
    match posts/{postId} { 
      match subcollection/{documentId} { 
          ... 
      } 
    } 
}
There is one important thing to notice when looking at these nested rules. The rules 
you add to the top level 
match posts/{postId}
 
do not
 apply to the inner 
match
 
statements. Security rules in Cloud Firestore do not cascade.
Saving Data on Android
Chapter 19: Securing Data in Cloud Firestore
raywenderlich.com
276

---