use super::*; impl Database {    /// Creates a new server in the given environment.    pub async fn create_server(&self, environment: &str) -> Result<ServerId> {        self.transaction(|tx| async move {            let server = server::ActiveModel {                environment: ActiveValue::set(environment.into()),                ..Default::default()            }            .insert(&*tx)            .await?;            Ok(server.id)        })        .await    }     /// Returns the IDs of resources associated with stale servers.    ///    /// A server is stale if it is in the specified `environment` and does not    /// match the provided `new_server_id`.    pub async fn stale_server_resource_ids(        &self,        environment: &str,        new_server_id: ServerId,    ) -> Result<(Vec<RoomId>, Vec<ChannelId>)> {        self.transaction(|tx| async move {            #[derive(Copy, Clone, Debug, EnumIter, DeriveColumn)]            enum QueryRoomIds {                RoomId,            }             #[derive(Copy, Clone, Debug, EnumIter, DeriveColumn)]            enum QueryChannelIds {                ChannelId,            }             let stale_server_epochs = self                .stale_server_ids(environment, new_server_id, &tx)                .await?;            let room_ids = room_participant::Entity::find()                .select_only()                .column(room_participant::Column::RoomId)                .distinct()                .filter(                    room_participant::Column::AnsweringConnectionServerId                        .is_in(stale_server_epochs.iter().copied()),                )                .into_values::<_, QueryRoomIds>()                .all(&*tx)                .await?;            let channel_ids = channel_buffer_collaborator::Entity::find()                .select_only()                .column(channel_buffer_collaborator::Column::ChannelId)                .distinct()                .filter(                    channel_buffer_collaborator::Column::ConnectionServerId                        .is_in(stale_server_epochs.iter().copied()),                )                .into_values::<_, QueryChannelIds>()                .all(&*tx)                .await?;             Ok((room_ids, channel_ids))        })        .await    }     /// Deletes any stale servers in the environment that don't match the `new_server_id`.    pub async fn delete_stale_servers(        &self,        environment: &str,        new_server_id: ServerId,    ) -> Result<()> {        self.transaction(|tx| async move {            server::Entity::delete_many()                .filter(                    Condition::all()                        .add(server::Column::Environment.eq(environment))                        .add(server::Column::Id.ne(new_server_id)),                )                .exec(&*tx)                .await?;            Ok(())        })        .await    }     async fn stale_server_ids(        &self,        environment: &str,        new_server_id: ServerId,        tx: &DatabaseTransaction,    ) -> Result<Vec<ServerId>> {        let stale_servers = server::Entity::find()            .filter(                Condition::all()                    .add(server::Column::Environment.eq(environment))                    .add(server::Column::Id.ne(new_server_id)),            )            .all(tx)            .await?;        Ok(stale_servers.into_iter().map(|server| server.id).collect())    }}