Wildcard in Firebase database rules

Question

Can we use wildcards in Firebase database rules? From my experiments, it doesn't seem like that's the case. Am I missing something or is that what's supposed to happen?

So, for example, I might have the same rules for all products_* entries and it would be easier to group them together using a wildcard.

To clarify, it's an web app and I am concerned with the database permissions that we set in the console. Can we use wildcard there ?

For example,

{
"rules": {
    "products_A": {
        <rules>
    },
    "products_B": {
        <rules>
    }
}

I would like to have only 1 set of rules like:

{
"rules": {
    "products_*": {
        <rules>
    }
}

Thanks.

Answer 1

Firebase offers a wildcard path used to represent ids and dynamic child keys. For example, $uid in the below rules is a 'wildcard' that allows the parameters within that node to refer to the parent node.

{
  "rules": {
    "users": {
      "$uid": {
        ".write": "$uid === auth.uid"
      }
    }
  }
}

in the above example, the $uid is the wildcard path for every user node within the /users node. Here is how the above rules expands per node

users
  uid_0 <--------|
                 V
    ".write": "uid_0 === auth.uid" //only user with uid = uid_0 can write
  uid_1
    ".write": "uid_1 === auth.uid" //only user with uid = uid_1 can write
  uid_2
    ".write": "uid_2 === auth.uid" //only user with uid = uid_1 can write

You can expand on this to provide a great level of flexibility. Say you want a certain set of users to be able to access a groups node. The group rules could be

  "rules": {
    "Groups": {
       "$group_id" : {
         ".read": "root.child('Allowed_Users/' + auth.uid).val() === $group_id",
         ".write": "root.child('Allowed_Users/' + auth.uid).val() === $group_id"
       }
    }

This limits access to each group node to a certain set of users, specified in the Allowed_Users node. The data in the Firebase database could look like:

Groups
   group_0
     //data
   group_1
     //data


Allowed_Users
   uid_0: group_0
   uid_1: group_0

Is this example, users uid_0 and uid_1 could read/write to group_0 but not read/write to group_1