This page builds on the concepts in
Structuring Security Rules
and
Writing Conditions for Security Rules
to explain how
Cloud Firestore Security Rules interact with queries. It takes a closer look at how
security rules affect the queries you can write and describes how to ensure your
queries use the same constraints as your security rules. This page also
describes how to write security rules to allow or deny queries based on query
properties like
limit
and
orderBy
.
Rules are not filters
When writing queries to retrieve documents, keep in mind that security rules are
not filters?queries are all or nothing. To save you time and resources,
Cloud Firestore evaluates a query against its potential result set
instead of the actual field values for all of your documents. If a query could
potentially return documents that the client does not have permission to read,
the entire request fails.
Queries and security rules
As the examples below demonstrate, you must write your queries to fit the
constraints of your security rules.
Secure and query documents based on
auth.uid
The following example demonstrates how to write a query to retrieve documents
protected by a security rule. Consider a database that contains a collection of
story
documents:
/stories/{storyid}
{
title: "A Great Story",
content: "Once upon a time...",
author: "some_auth_id",
published: false
}
In addition to the
title
and
content
fields, each document stores the
author
and
published
fields to use for access control. These examples assume
the app uses
Firebase Authentication
to set the
author
field
to the UID of the user who created the document. Firebase
Authentication also populates the
request.auth
variable in
the security rules.
The following security rule uses the
request.auth
and
resource.data
variables to restrict read and write access for each
story
to its author:
service cloud.firestore {
match /databases/{database}/documents {
match /stories/{storyid} {
// Only the authenticated user who authored the document can read or write
allow read, write: if request.auth != null && request.auth.uid == resource.data.author;
}
}
}
Suppose that your app includes a page that shows the user a list of
story
documents that they authored. You might expect that you could use the following
query to populate this page. However, this query will fail, because it does not
include the same constraints as your security rules:
Invalid
: Query constraints do not match
security rules constraints
// This query will fail
db.collection("stories").get()
The query fails
even if
the current user actually is the author of every
story
document. The reason for this behavior is that when
Cloud Firestore applies your security rules, it evaluates the query
against its
potential
result set, not against the
actual
properties of
documents in your database. If a query could
potentially
include documents
that violate your security rules, the query will fail.
In contrast, the following query succeeds, because it includes the same
constraint on the
author
field as the security rules:
Valid
: Query constraints match security
rules constraints
var user = firebase.auth().currentUser;
db.collection("stories").where("author", "==", user.uid).get()
Secure and query documents based on a field
To further demonstrate the interaction between queries and rules, the security
rules below expand read access for the
stories
collection to allow any user to
read
story
documents where the
published
field is set to
true
.
service cloud.firestore {
match /databases/{database}/documents {
match /stories/{storyid} {
// Anyone can read a published story; only story authors can read unpublished stories
allow read: if resource.data.published == true || (request.auth != null && request.auth.uid == resource.data.author);
// Only story authors can write
allow write: if request.auth != null && request.auth.uid == resource.data.author;
}
}
}
The query for published pages must include the same constraints as the security
rules:
db.collection("stories").where("published", "==", true).get()
The query constraint
.where("published", "==", true)
guarantees that
resource.data.published
is
true
for any result. Therefore, this query
satisfies the security rules and is allowed to read data.
OR
queries
When evaluating a logical
OR
query (
or
,
in
, or
array-contains-any
)
against a ruleset, Cloud Firestore evaluates each comparison value
separately. Each comparison value must meet the security rule constraints. For
example, for the
following rule:
match /mydocuments/{doc} {
allow read: if resource.data.x > 5;
}
Invalid
: Query does not guarantee that
x > 5
for all potential documents
// These queries will fail
query(db.collection("mydocuments"),
or(where("x", "==", 1),
where("x", "==", 6)
)
)
query(db.collection("mydocuments"),
where("x", "in", [1, 3, 6, 42, 99])
)
Valid
: Query guarantees that
x > 5
for all potential documents
query(db.collection("mydocuments"),
or(where("x", "==", 6),
where("x", "==", 42)
)
)
query(db.collection("mydocuments"),
where("x", "in", [6, 42, 99, 105, 200])
)
Evaluating constraints on queries
Your security rules can also accept or deny queries based on their constraints.
The
request.query
variable contains the
limit
,
offset
,
and
orderBy
properties of a query. For example, your security rules
can deny any query that doesn't limit the maximum number of documents
retrieved to a certain range:
allow list: if request.query.limit <= 10;
The following ruleset demonstrates how to write security rules that evaluate
constraints placed on queries. This example expands the previous
stories
ruleset with the following changes:
- The ruleset separates the read rule into rules for
get
and
list
.
- The
get
rule restricts retrieval of single documents to public documents or
documents the user authored.
- The
list
rule applies the same restrictions as
get
but for queries. It
also checks the query limit, then denies any query without a limit or with a
limit greater than 10.
- The ruleset defines an
authorOrPublished()
function to avoid code
duplication.
service cloud.firestore {
match /databases/{database}/documents {
match /stories/{storyid} {
// Returns `true` if the requested story is 'published'
// or the user authored the story
function authorOrPublished() {
return resource.data.published == true || request.auth.uid == resource.data.author;
}
// Deny any query not limited to 10 or fewer documents
// Anyone can query published stories
// Authors can query their unpublished stories
allow list: if request.query.limit <= 10 &&
authorOrPublished();
// Anyone can retrieve a published story
// Only a story's author can retrieve an unpublished story
allow get: if authorOrPublished();
// Only a story's author can write to a story
allow write: if request.auth.uid == resource.data.author;
}
}
}
Collection group queries and security rules
By default, queries are scoped to a single collection and they retrieve results
only from that collection. With
collection group queries
, you can
retrieve results from a collection group consisting of all collections with the
same ID. This section describes how to secure your collection group queries
using security rules.
Secure and query documents based on collection groups
In your security rules, you must explicitly allow
collection group queries by writing a rule for the collection group:
- Make sure
rules_version = '2';
is the first line of your ruleset. Collection
group queries require the
new recursive wildcard
{name=**}
behavior of security
rules version 2.
- Write a rule for you collection group using
match /{path=**}/
[COLLECTION_ID]
/{doc}
.
For example, consider a forum organized into
forum
documents containing
posts
subcollections:
/forums/{forumid}/posts/{postid}
{
author: "some_auth_id",
authorname: "some_username",
content: "I just read a great story.",
}
In this application, we make posts editable by their owners and readable by
authenticated users:
service cloud.firestore {
match /databases/{database}/documents {
match /forums/{forumid}/posts/{post} {
// Only authenticated users can read
allow read: if request.auth != null;
// Only the post author can write
allow write: if request.auth != null && request.auth.uid == resource.data.author;
}
}
}
Any authenticated user can retrieve the posts of any single forum:
db.collection("forums/technology/posts").get()
But what if you want to show the current user their posts across all forums?
You can use a
collection group query
to retrieve
results from all
posts
collections:
var user = firebase.auth().currentUser;
db.collectionGroup("posts").where("author", "==", user.uid).get()
In your security rules, you must allow this query by
writing a read or list rule for the
posts
collection group:
rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
// Authenticated users can query the posts collection group
// Applies to collection queries, collection group queries, and
// single document retrievals
match /{path=**}/posts/{post} {
allow read: if request.auth != null;
}
match /forums/{forumid}/posts/{postid} {
// Only a post's author can write to a post
allow write: if request.auth != null && request.auth.uid == resource.data.author;
}
}
}
Note, however, that these rules will apply to all collections with ID
posts
,
regardless of hierarchy. For example, these rules apply to all of the following
posts
collections:
/posts/{postid}
/forums/{forumid}/posts/{postid}
/forums/{forumid}/subforum/{subforumid}/posts/{postid}
Secure collection group queries based on a field
Like single-collection queries, collection group queries must also meet the
constraints set by your security rules. For example, we can add a
published
field to each forum post like we did in the
stories
example above:
/forums/{forumid}/posts/{postid}
{
author: "some_auth_id",
authorname: "some_username",
content: "I just read a great story.",
published: false
}
We can then write rules for the
posts
collection group based on the
published
status and the post
author
:
rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
// Returns `true` if the requested post is 'published'
// or the user authored the post
function authorOrPublished() {
return resource.data.published == true || request.auth.uid == resource.data.author;
}
match /{path=**}/posts/{post} {
// Anyone can query published posts
// Authors can query their unpublished posts
allow list: if authorOrPublished();
// Anyone can retrieve a published post
// Authors can retrieve an unpublished post
allow get: if authorOrPublished();
}
match /forums/{forumid}/posts/{postid} {
// Only a post's author can write to a post
allow write: if request.auth.uid == resource.data.author;
}
}
}
With these rules, Web, Apple, and Android clients can make the following queries:
Anyone can retrieve published posts in a forum:
db.collection("forums/technology/posts").where('published', '==', true).get()
Anyone can retrieve an author's published posts across all forums:
db.collectionGroup("posts").where("author", "==", "some_auth_id").where('published', '==', true).get()
Authors can retrieve all their published and unpublished posts across all
forums:
var user = firebase.auth().currentUser;
db.collectionGroup("posts").where("author", "==", user.uid).get()
Secure and query documents based on collection group and document path
In some cases, you might want to restrict collection group queries based on
document path. To create these restrictions, you can use the same techniques for
securing and querying documents based on a field.
Consider an application that keeps track of each user's transactions
among several stock and cryptocurrency exchanges:
/users/{userid}/exchange/{exchangeid}/transactions/{transaction}
{
amount: 100,
exchange: 'some_exchange_name',
timestamp: April 1, 2019 at 12:00:00 PM UTC-7,
user: "some_auth_id",
}
Notice the
user
field. Even though we know which user owns a
transaction
document from the document's path, we duplicate this information in each
transaction
document because it allows us to do two things:
Write collection group queries that are restricted to documents that include
a specific
/users/{userid}
in their document path. For example:
var user = firebase.auth().currentUser;
// Return current user's last five transactions across all exchanges
db.collectionGroup("transactions").where("user", "==", user).orderBy('timestamp').limit(5)
Enforce this restriction for all queries on the
transactions
collection
group so one user cannot retrieve another user's
transaction
documents.
We enforce this restriction in our security rules and include data validation
for the
user
field:
rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
match /{path=**}/transactions/{transaction} {
// Authenticated users can retrieve only their own transactions
allow read: if resource.data.user == request.auth.uid;
}
match /users/{userid}/exchange/{exchangeid}/transactions/{transaction} {
// Authenticated users can write to their own transactions subcollections
// Writes must populate the user field with the correct auth id
allow write: if userid == request.auth.uid && request.data.user == request.auth.uid
}
}
}
Next steps