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Firebase Database Quickstart

Introduction

Getting Started

Result

Data Model

This quickstart demonstrates a simple data model for a social application. While this data model uses some of the Firebase best practices, it has some known tradeoffs made for simplicity that would not scale to very large numbers of users.

The database has four "root" nodes:

  • users - a list of User objects, keyed by user ID. So /users/<ID>/email is the email address of the user with id=<ID>.
  • posts - a list of Post objects, keyed by randomly generated push ID. Each Post contains the uid and author properties to determine the identity of the author without a JOIN-style query.
    • Posts contain a stars property which is a Map of user IDs to boolean values. If /posts/<POST-ID>/stars/<USER-ID> is true, this means the user with ID <USER-ID> has starred the post with ID <POST-ID>. This data nesting makes it easy to tell if a specific user has already starred a specific post, but would not scale to large numbers of stars per post as it would make loading the Post data more expensive.
  • user-posts - a list of posts by the user. /user-posts/<USER-ID> is a list of all posts made by a specific user, keyed by the same push ID used in the posts tree. This makes it easy to query "all posts by a specific user" without filtering through all Post objects.
  • post-comments - comments on a particular posts, where /post-comments/<POST-ID> is a list of all comments on post with id <POST-ID>. Each comment has a randomly generated push key. By keeping this data in its own tree rather than nesting it under posts, we make it possible to load a post without loading all comments while still having a known path to access all comments for a particular post.

Database Rules

Below are some samples rules that limit access and validate data:

{
  "rules": {
    // User profiles are only readable/writable by the user who owns it
    "users": {
      "$UID": {
        ".read": "auth.uid == $UID",
        ".write": "auth.uid == $UID"
      }
    },

    // Posts can be read by anyone but only written by logged-in users.
    "posts": {
      ".read": true,
      ".write": "auth.uid != null",

      "$POSTID": {
        // UID must match logged in user and is fixed once set
        "uid": {
          ".validate": "(data.exists() && data.val() == newData.val()) || newData.val() == auth.uid"
        },

        // User can only update own stars
        "stars": {
          "$UID": {
              ".validate": "auth.uid == $UID"
          }
        }
      }
    },

    // User posts can be read by anyone but only written by the user that owns it,
    // and with a matching UID
    "user-posts": {
      ".read": true,

      "$UID": {
        "$POSTID": {
          ".write": "auth.uid == $UID",
        	".validate": "data.exists() || newData.child('uid').val() == auth.uid"
        }
      }
    },


    // Comments can be read by anyone but only written by a logged in user
    "post-comments": {
      ".read": true,
      ".write": "auth.uid != null",

      "$POSTID": {
        "$COMMENTID": {
          // UID must match logged in user and is fixed once set
          "uid": {
              ".validate": "(data.exists() && data.val() == newData.val()) || newData.val() == auth.uid"
          }
        }
      }
    }
  }
}

Support

License

Copyright 2016 Google, Inc.

Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.