Access Policies​

Defining a global​

To start, we’ll add a global variable to our schema. We’ll use this global to represent the identity of the user executing the query.

  global current_user: uuid;

  type User {
    required email: str { constraint exclusive; };
  }

  type BlogPost {
    required title: str;
    required author: User;
  }

Global variables are a generic mechanism for providing context to a query. Most commonly, they are used in the context of access policies.

The value of these variables is attached to the client you use to execute queries. The exact API depends on which client library you’re using:

import createClient from 'edgedb';

const client = createClient().withGlobals({
  current_user: '2141a5b4-5634-4ccc-b835-437863534c51',
});

await client.query(`select global current_user;`);

from edgedb import create_client

client = create_client().with_globals({
    'current_user': '580cc652-8ab8-4a20-8db9-4c79a4b1fd81'
})

result = client.query("""
    select global current_user;
""")

package main

import (
  "context"
  "fmt"
  "log"

  "github.com/edgedb/edgedb-go"
)

func main() {
  ctx := context.Background()
  client, err := edgedb.CreateClient(ctx, edgedb.Options{})
  if err != nil {
    log.Fatal(err)
  }
  defer client.Close()

  id, err := edgedb.ParseUUID("2141a5b4-5634-4ccc-b835-437863534c51")
  if err != nil {
    log.Fatal(err)
  }

  var result edgedb.UUID
  err = client.
    WithGlobals(map[string]interface{}{"current_user": id}).
    QuerySingle(ctx, "SELECT global current_user;", &result)
  if err != nil {
    log.Fatal(err)
  }

  fmt.Println(result)
}

use uuid::Uuid;

let client = edgedb_tokio::create_client()
    .await
    .expect("Client should init")
    .with_globals_fn(|c| {
        c.set(
            "current_user",
            Value::Uuid(
                Uuid::parse_str("2141a5b4-5634-4ccc-b835-437863534c51")
                    .expect("Uuid should have parsed"),
            ),
        )
    });
client
    .query_required_single::<Uuid, _>("select global current_user;", &())
    .await
    .expect("Returning value");

Defining a policy​

Let’s add a policy to our sample schema.

  global current_user: uuid;

  type User {
    required email: str { constraint exclusive; };
  }

  type BlogPost {
    required title: str;
    required author: User;

    access policy author_has_full_access
      allow all
      using (global current_user ?= .author.id);
  }

Let’s break down the access policy syntax piece-by-piece. This policy grants full read-write access (all) to the author of each BlogPost. No one else will be able to edit, delete, or view this post.

• access policy: The keyword used to declare a policy inside an object type.

• author_has_full_access: The name of this policy; could be any string.

• allow: The kind of policy; could be allow or deny

• all: The set of operations being allowed/denied; a comma-separated list of the following: all, select, insert, delete, update, update read, update write.

• using (<expr>): A boolean expression. Think of this as a filter expression that defines the set of objects to which the policy applies.

Let’s do some experiments.

db> 

insert User { email := "test@edgedb.com" };

{default::User {id: be44b326-03db-11ed-b346-7f1594474966}}

db> 

set global current_user := <uuid>"be44b326-03db-11ed-b346-7f1594474966";

OK: SET GLOBAL

db> 
... 
... 
... 

insert BlogPost {
   title := "My post",
   author := (select User filter .id = global current_user)
 };

{default::BlogPost {id: e76afeae-03db-11ed-b346-fbb81f537ca6}}

We’ve created a User, set the value of current_user to its id, and created a new BlogPost. When we try to select all BlogPost objects, we’ll see the post we just created.

db> 

select BlogPost;

{default::BlogPost {id: e76afeae-03db-11ed-b346-fbb81f537ca6}}

db> 

select count(BlogPost);

{1}

Now let’s unset current_user and see what happens.

db> 

set global current_user := {};

OK: SET GLOBAL

db> 

select BlogPost;

{}

db> 

select count(BlogPost);

{0}

Now select BlogPost returns zero results. We can only select the posts written by the user specified by current_user. When current_user has no value, we can’t read any posts.

The access policies use global variables to define a “subgraph” of data that is visible to a particular query.

Policy types​

For the most part, the policy types correspond to EdgeQL’s statement types:

• select: Applies to all queries; objects without a select permission cannot be modified either.

• insert: Applies to insert queries; executed post-insert. If an inserted object violates the policy, the query will fail.

• delete: Applies to delete queries.

• update: Applies to update queries.

Additionally, the update operation can broken down into two sub-policies: update read and update write.

• update read: This policy restricts which objects can be updated. It runs pre-update; that is, this policy is executed before the updates have been applied.

• update write: This policy restricts how you update the objects; you can think of it as a post-update validity check. This could be used to prevent a User from transferring a BlogPost to another User.

Finally, there’s an umbrella policy that can be used as a shorthand for all the others.

• all: A shorthand policy that can be used to allow or deny full read/ write permissions. Exactly equivalent to select, insert, update, delete.

Resolution order​

An object type can contain an arbitrary number of access policies, including several conflicting allow and deny policies. EdgeDB uses a particular algorithm for resolving these policies.

1. When no policies are defined on a given object type, all objects of that type can be read or modified by any appropriately authenticated connection.

2. EdgeDB then applies all allow policies. Each policy grants a permission that is scoped to a particular set of objects as defined by the using clause. Conceptually, these permissions are merged with the union / or operator to determine the set of allowable actions.

3. After the allow policies are resolved, the deny policies can be used to carve out exceptions to the allow rules. Deny rules supersede allow rules! As before, the set of objects targeted by the policy is defined by the using clause.

4. This results in the final access level: a set of objects targetable by each of select, insert, update read, update write, and delete.

Currently, by default the access policies affect the values visible in expressions of other access policies. This means that they can affect each other in various ways. Because of this, great care needs to be taken when creating access policies based on objects other than the ones they are defined on. For example:

global current_user_id: uuid;
global current_user := (
  select User filter .id = global current_user_id
);

type User {
  required email: str { constraint exclusive; };
  required is_admin: bool { default := false };

  access policy admin_only
    allow all
    using (global current_user.is_admin ?? false);
}

type BlogPost {
  required title: str;
  author: User;

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
}

In the above schema only the admin will see a non-empty author link, because only the admin can see any user objects at all. This means that instead of making BlogPost visible to its author, all non-admin authors won’t be able to see their own posts. The above issue can be remedied by making the current user able to see their own User record.

Custom error messagesNew​

When you run a query that attempts a write and is restricted by an access policy, you will get a generic error message.

edgedb error: AccessPolicyError: access policy violation on insert of
<type>

If you have multiple access policies, it can be useful to know which policy is restricting your query and provide a friendly error message. You can do this by adding a custom error message to your policy.

global current_user_id -> uuid;
global current_user := (
  select User filter .id = global current_user_id
);

type User {
  required property email -> str { constraint exclusive; };
  required property is_admin -> bool { default := false };

  access policy admin_only
    allow all
    using (global current_user.is_admin ?? false) {
      errmessage := 'Only admins may query Users'
    };
}

type BlogPost {
  required property title -> str;
  link author -> User;

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id) {
      errmessage := 'BlogPosts may only be queried by their authors'
    };
}

Now if you attempt, for example, a User insert as a non-admin user, you will receive this error:

edgedb error: AccessPolicyError: access policy violation on insert of
default::User (Only admins may query Users)

Disabling policies​

You may disable all access policies by setting the apply_access_policies configuration parameter to false.

You may also toggle access policies using the “Disable Access Policies” checkbox in the “Config” dropdown in the EdgeDB UI (accessible by running the CLI command edgedb ui from inside your project). This is the most convenient way to temporarily disable access policies since it applies only to your UI session.

Examples​

Blog posts are publicly visible if published but only writable by the author.

global current_user: uuid;

type User {
  required email: str { constraint exclusive; };
}

type BlogPost {
  required title: str;
  required author: User;
  required published: bool { default := false }

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
  access policy visible_if_published
    allow select
    using (.published);
}

Blog posts are visible to friends but only modifiable by the author.

global current_user: uuid;

type User {
  required email: str { constraint exclusive; };
  multi friends: User;
}

type BlogPost {
  required title: str;
  required author: User;

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
  access policy friends_can_read
    allow select
    using ((global current_user in .author.friends.id) ?? false);
}

Blog posts are publicly visible except to users that have been blocked by the author.

type User {
  required email: str { constraint exclusive; };
  multi blocked: User;
}

type BlogPost {
  required title: str;
  required author: User;

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
  access policy anyone_can_read
    allow select;
  access policy exclude_blocked
    deny select
    using ((global current_user in .author.blocked.id) ?? false);
}

“Disappearing” posts that become invisible after 24 hours.

type User {
  required email: str { constraint exclusive; };
}

type BlogPost {
  required title: str;
  required author: User;
  required created_at: datetime {
    default := datetime_of_statement() # non-volatile
  }

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
  access policy hide_after_24hrs
    allow select
    using (datetime_of_statement() - .created_at < <duration>'24 hours');
}

type User {
  required email: str { constraint exclusive; };
  multi link posts := .<author[is BlogPost]
}

type BlogPost {
  required title: str;
  required author: User;

  access policy author_has_full_access
    allow all
    using (global current_user ?= .author.id);
  access policy max_posts_limit
    deny insert
    using (count(.author.posts) > 500);
}