Session-Aware Computed Fields

Add session-aware computed fields to a table, with a community membership example

Two session-aware computed fields on the communities table in the react-demo:

is_member — boolean. Does the current user belong to this community?
my_joined_at — timestamptz. When did the current user join, or null.

See Communities.tsx for the UI, and Computed Fields for the underlying feature.

The SQL functions

CREATE OR REPLACE FUNCTION public.community_is_member(
  community_row public.communities,
  user_session json
)
RETURNS boolean
LANGUAGE sql
STABLE
AS $$
  SELECT EXISTS (
    SELECT 1
    FROM public.community_members
    WHERE community_members.community_id = community_row.id
      AND community_members.user_id = (user_session ->> 'x-hasura-user-id')::uuid
  );
$$;

CREATE OR REPLACE FUNCTION public.community_my_joined_at(
  community_row public.communities,
  user_session json
)
RETURNS timestamptz
LANGUAGE sql
STABLE
AS $$
  SELECT joined_at
  FROM public.community_members
  WHERE community_members.community_id = community_row.id
    AND community_members.user_id = (user_session ->> 'x-hasura-user-id')::uuid
  LIMIT 1;
$$;

Registering the computed fields

session_argument: user_session binds the request’s session JSON to the function’s user_session parameter and hides it from the GraphQL schema.

computed_fields:
  - name: is_member
    definition:
      function:
        name: community_is_member
        schema: public
      session_argument: user_session
    comment: Whether the current user is a member of this community
  - name: my_joined_at
    definition:
      function:
        name: community_my_joined_at
        schema: public
      session_argument: user_session
    comment: When the current user joined this community, or null if they aren't a member

In the dashboard: Database → communities → Edit GraphQL → Computed Fields. Set Session Argument to user_session for both.

Setting the session argument on a computed field

Granting access

select_permissions:
  - role: user
    permission:
      columns:
        - id
        - name
        - description
        - created_at
        - updated_at
      computed_fields:
        - is_member
        - my_joined_at
      filter: {}

See Permissions.

Querying

query GetCommunities {
  communities {
    id
    name
    description
    is_member
    my_joined_at
  }
}

Using the values in the UI

Communities list showing membership and join time

is_member drives Join/Leave; my_joined_at renders as a small muted line under Leave for member rows:

const isMember = (community: Community) => community.is_member;

// ...

<td>
  {isMember(community) ? (
    <>
      <button
        type="button"
        className="btn btn-secondary"
        onClick={() => handleLeave(community.id)}
      >
        Leave
      </button>
      {community.my_joined_at && (
        <div style={{ fontSize: '0.8em', opacity: 0.7, marginTop: '4px' }}>
          joined {formatRelativeTime(community.my_joined_at)}
        </div>
      )}
    </>
  ) : (
    <button
      type="button"
      className="btn btn-primary"
      onClick={() => handleJoin(community.id)}
    >
      Join
    </button>
  )}
</td>

Computed Fields — the underlying feature
Permissions — granting role access to a field
Full source — Communities.tsx on GitHub