docs/_develop/radiks-collaborate.md

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# Collaborate with groups
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A key feature of Radiks is support for private collaboration between multiple users.  Supporting collaboration with client-side encryption and user-owned storage can be complicated, but the patterns to implement it are generally the same among most applications. Radiks supplies interfaces for collaboration, making it easy to build private, collaborative apps.

You use the <a href="https://github.com/blockstack/radiks/blob/master/src/models/user-group.ts" target="_blank"><code>UserGroup</code></a> class to build a collaborative group with Radiks. In this section, you learn about this class.

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## Understand the UserGroup workflow

The key model behind a collaborative group is `UserGroup`. By default, it only has one attribute, `name`, which is encrypted. You can subclass  `UserGroup` with different attributes as needed.

The general workflow for creating a collaborative group that can share and edit encrypted models is as follows:

1. The admin of the group creates a new `UserGroup`.
   This group acts as the 'hub' and controls the logic around inviting and removing users.
2. The admin invites one or more other users to a group:
    * The admin specifies the username of the user they want to invite
    * Radiks looks up the user's public key
    * Radiks creates an 'invitation' that is encrypted with the user's public key, and contains information about the `UserGroup`
3. When the invited user 'activates' an invitation, they create a `GroupMembership`. 
   They use this membership instance to reference information (such as private keys and signing keys) related to the group.

As they participate in a group, the group's members can create and update models that are related to the group. These models **must** contain a `userGroupId` attribute used to reference the group. This allows Radiks to know which keys to use for encryption and signing.

When needed, the group admin can remove a user from a group. To remove a user from the group, the admin creates a new private key for signing and encryption. Then, the admin updates the `GroupMembership` of all users _except_ the user they just removed. This update-and-remove action is also known as rotating the key.

After a key is rotated, all new and updated models must use the new key for signing. Radiks-server validates all group-related models to ensure that they're signed with the most up-to-date key.

## Work with a UserGroup

This section details the methods on the <a href="https://github.com/blockstack/radiks/blob/master/src/models/user-group.ts" target="_blank"><code>UserGroup</code> class you can use to create, add members to, and query a group.

### Create a UserGroup

To create a `UserGroup`, you must import the class into your application from `radiks`:

```javascript
import { UserGroup } from 'radiks';

// ...
```

Calling `create` on a new `UserGroup` will create the group and activate an invitation for the group's creator.
 

```javascript
const group = new UserGroup({ name: 'My Group Name' });
await group.create();
```

A group's creator is also the group's admin.


### Invite users to become members

Use the `makeGroupMembership` method on a `UserGroup` instance to invite a user. The only argument passed to this method is the user's `username`.

```javascript
import { UserGroup } from 'radiks';

const group = await UserGroup.findById(myGroupId);
const usernameToInvite = 'hankstoever.id';
const invitation = await group.makeGroupMembership(usernameToInvite);
console.log(invitation._id); // the ID used to later activate an invitation
```

### Accept an invitation

Use the `activate` method on a `GroupInvitation` instance to activate an invitation on behalf of a user:

```javascript
import { GroupInvitation } from 'radiks';

const invitation = await GroupInvitation.findById(myInvitationID);
await invitation.activate();
```

## View all activated UserGroups for the current user

Call `UserGroup.myGroups` to fetch all groups that the current user is a member of:

```javascript
import { UserGroup } from 'radiks';

const groups = await UserGroup.myGroups();
```

## Find a UserGroup

Use the method `UserGroup.find(id)` when fetching a specific UserGroup. This method has extra boilerplate to handle decrypting the model, because the private keys may need to be fetched from different models.

```javascript
const group = await UserGroup.find('my-id-here');
```