+ # Return a query with read permissions restricted to the union of of the
+ # permissions of the members of users_list, i.e. if something is readable by
+ # any user in users_list, it will be readable in the query returned by this
+ # function.
+ def self.readable_by(*users_list)
+ # Get rid of troublesome nils
+ users_list.compact!
+
+ # Check if any of the users are admin. If so, we're done.
+ if users_list.select { |u| u.is_admin }.empty?
+
+ # Collect the uuids for each user and any groups readable by each user.
+ user_uuids = users_list.map { |u| u.uuid }
+ uuid_list = user_uuids + users_list.flat_map { |u| u.groups_i_can(:read) }
+ sanitized_uuid_list = uuid_list.
+ collect { |uuid| sanitize(uuid) }.join(', ')
+ sql_conds = []
+ sql_params = []
+ or_object_uuid = ''
+
+ # This row is owned by a member of users_list, or owned by a group
+ # readable by a member of users_list
+ # or
+ # This row uuid is the uuid of a member of users_list
+ # or
+ # A permission link exists ('write' and 'manage' implicitly include
+ # 'read') from a member of users_list, or a group readable by users_list,
+ # to this row, or to the owner of this row (see join() below).
+ permitted_uuids = "(SELECT head_uuid FROM links WHERE link_class='permission' AND tail_uuid IN (#{sanitized_uuid_list}))"
+
+ sql_conds += ["#{table_name}.owner_uuid in (?)",
+ "#{table_name}.uuid in (?)",
+ "#{table_name}.uuid IN #{permitted_uuids}"]
+ sql_params += [uuid_list, user_uuids]
+
+ if self == Link and users_list.any?
+ # This row is a 'permission' or 'resources' link class
+ # The uuid for a member of users_list is referenced in either the head
+ # or tail of the link
+ sql_conds += ["(#{table_name}.link_class in (#{sanitize 'permission'}, #{sanitize 'resources'}) AND (#{table_name}.head_uuid IN (?) OR #{table_name}.tail_uuid IN (?)))"]
+ sql_params += [user_uuids, user_uuids]
+ end
+
+ if self == Log and users_list.any?
+ # Link head points to the object described by this row
+ sql_conds += ["#{table_name}.object_uuid IN #{permitted_uuids}"]
+
+ # This object described by this row is owned by this user, or owned by a group readable by this user
+ sql_conds += ["#{table_name}.object_owner_uuid in (?)"]
+ sql_params += [uuid_list]
+ end
+
+ # Link head points to this row, or to the owner of this row (the thing to be read)
+ #
+ # Link tail originates from this user, or a group that is readable by this
+ # user (the identity with authorization to read)
+ #
+ # Link class is 'permission' ('write' and 'manage' implicitly include 'read')
+ where(sql_conds.join(' OR '), *sql_params)
+ else
+ # At least one user is admin, so don't bother to apply any restrictions.
+ self