Access parent documents field in Firestore rules

Question

I\'m implementing a recipe book in Firestore where every user is able to see all the recipes all users created but only the original author of the recipe is allowed to edit or d

Answer 1

Dan's answer above works great! Just for reference, in my case I only needed the root parent document ID, you can use the variable from the match statement above the nested one, like this:

service cloud.firestore {
  match /databases/{database}/documents {

    function isSignedIn() {
      return request.auth != null;
    }

    match /ListOfRecipes/{recipeID} {
        allow read, create: if isSignedIn();
        allow update, delete: if resource.data.creatorUID == request.auth.uid;

        match /List/{list} {
            allow read: if isSignedIn();
            allow write: if  recipeID == 'XXXXX';
        }
    }
  }
}