Enum DatabaseConnection 

pub enum DatabaseConnection {
    Disconnected,
}

Handle a database connection depending on the backend enabled by the feature flags. This creates a database pool. This will be Clone unless the feature flag mock is enabled.

Variants

Disconnected

The connection to the database has been severed

Implementations

impl DatabaseConnection

pub fn set_metric_callback<F>(&mut self, _callback: F)

where F: Fn(&Info<'_>) + Send + Sync + 'static,

Sets a callback to metric this connection

pub async fn ping(&self) -> Result<(), DbErr>

Checks if a connection to the database is still valid.

pub async fn close(self) -> Result<(), DbErr>

Explicitly close the database connection. See Self::close_by_ref for usage with references.

pub async fn close_by_ref(&self) -> Result<(), DbErr>

Explicitly close the database connection

Trait Implementations

impl Clone for DatabaseConnection

fn clone(&self) -> DatabaseConnection

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl ConnectionTrait for DatabaseConnection

fn get_database_backend(&self) -> DatabaseBackend

Fetch the database backend as specified in DbBackend. This depends on feature flags enabled.

fn execute<'life0, 'async_trait>( &'life0 self, stmt: Statement, ) -> Pin<Box<dyn Future<Output = Result<ExecResult, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, DatabaseConnection: 'async_trait,

Execute a Statement

fn execute_unprepared<'life0, 'life1, 'async_trait>( &'life0 self, sql: &'life1 str, ) -> Pin<Box<dyn Future<Output = Result<ExecResult, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, 'life1: 'async_trait, DatabaseConnection: 'async_trait,

Execute a unprepared Statement

fn query_one<'life0, 'async_trait>( &'life0 self, stmt: Statement, ) -> Pin<Box<dyn Future<Output = Result<Option<QueryResult>, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, DatabaseConnection: 'async_trait,

Execute a Statement and return a query

fn query_all<'life0, 'async_trait>( &'life0 self, stmt: Statement, ) -> Pin<Box<dyn Future<Output = Result<Vec<QueryResult>, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, DatabaseConnection: 'async_trait,

Execute a Statement and return a collection Vec<QueryResult> on success

fn support_returning(&self) -> bool

Check if the connection supports RETURNING syntax on insert and update

fn is_mock_connection(&self) -> bool

Check if the connection is a test connection for the Mock database

impl DatasetConfigDb for DatabaseConnection

fn get_by_dataset_id<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<DatasetConfiguration>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn upsert<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, patch: DatasetConfigurationPatch, ) -> Pin<Box<dyn Future<Output = Result<DatasetConfiguration, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

impl Debug for DatabaseConnection

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for DatabaseConnection

fn default() -> DatabaseConnection

Returns the “default value” for a type.

impl DeleteDb for DatabaseConnection

fn get_data<'life0, 'async_trait>( &'life0 self, id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<Data>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn delete_data<'life0, 'async_trait>( &'life0 self, id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn count_data_dataset_links<'life0, 'async_trait>( &'life0 self, data_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<usize, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn list_datasets_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn get_dataset_by_name<'life0, 'life1, 'async_trait>( &'life0 self, name: &'life1 str, owner_id: Uuid, tenant_id: Option<Uuid>, ) -> Pin<Box<dyn Future<Output = Result<Option<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

fn get_dataset_data<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<Data>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn count_dataset_data<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<usize, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Count the number of data items linked to a dataset without loading them.

fn list_datasets_by_owner<'life0, 'async_trait>( &'life0 self, owner_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn list_datasets<'life0, 'async_trait>( &'life0 self, ) -> Pin<Box<dyn Future<Output = Result<Vec<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn delete_dataset<'life0, 'async_trait>( &'life0 self, id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn detach_data_from_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, data_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn delete_pipeline_runs_by_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<u64, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete all pipeline_runs rows for a given dataset.

fn clear_pipeline_status_for_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<usize, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Clear pipeline_status JSON entries keyed by dataset_id from all Data records linked to that dataset.

fn clear_cognify_pipeline_status_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Clear only the cognify_pipeline key from the pipeline_status JSON of a single Data record, removing only the entry keyed by dataset_id.

fn get_nodes_by_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<GraphNode>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Get all provenance node rows for a dataset.

fn get_edges_by_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<GraphEdge>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Get all provenance edge rows for a dataset.

fn get_unique_nodes_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<GraphNode>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Get nodes belonging to (data_id, dataset_id) whose slug is NOT shared with other data items in the same dataset. Safe for targeted deletion.

fn get_unique_edges_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<GraphEdge>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Get edges belonging to (data_id, dataset_id) whose slug is NOT shared with other data items in the same dataset.

fn delete_provenance_nodes_for_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete all provenance node rows for a dataset.

fn delete_provenance_edges_for_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete all provenance edge rows for a dataset.

fn delete_provenance_nodes_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete provenance node rows for a specific (data_id, dataset_id) pair.

fn delete_provenance_edges_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete provenance edge rows for a specific (data_id, dataset_id) pair.

fn get_provenance_node_count_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<usize, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Count provenance node rows for a specific (data_id, dataset_id) pair.

fn get_provenance_edge_count_for_data<'life0, 'async_trait>( &'life0 self, data_id: Uuid, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<usize, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Count provenance edge rows for a specific (data_id, dataset_id) pair.

fn delete_search_history_for_user<'life0, 'async_trait>( &'life0 self, user_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<u64, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete all search history (queries + cascaded results) for a user.

fn delete_all_search_history<'life0, 'async_trait>( &'life0 self, ) -> Pin<Box<dyn Future<Output = Result<u64, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete all search history (queries + cascaded results).

fn count_search_history_for_user<'life0, 'async_trait>( &'life0 self, user_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<u64, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Count search history query rows for a specific user.

fn count_all_search_history<'life0, 'async_trait>( &'life0 self, ) -> Pin<Box<dyn Future<Output = Result<u64, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Count all search history query rows.

impl IngestDb for DatabaseConnection

fn get_dataset_by_name<'life0, 'life1, 'async_trait>( &'life0 self, name: &'life1 str, owner_id: Uuid, tenant_id: Option<Uuid>, ) -> Pin<Box<dyn Future<Output = Result<Option<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

fn get_dataset<'life0, 'async_trait>( &'life0 self, id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Look up a dataset by its UUID.

fn create_dataset<'life0, 'async_trait>( &'life0 self, dataset: Dataset, ) -> Pin<Box<dyn Future<Output = Result<Dataset, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn list_datasets_by_owner<'life0, 'async_trait>( &'life0 self, owner_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<Dataset>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

List all datasets owned by the given user.

fn get_data<'life0, 'async_trait>( &'life0 self, id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<Data>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn create_data<'life0, 'async_trait>( &'life0 self, d: Data, ) -> Pin<Box<dyn Future<Output = Result<Data, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn attach_data_to_dataset<'life0, 'async_trait>( &'life0 self, dataset_id: Uuid, data_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

fn update_last_accessed<'life0, 'life1, 'async_trait>( &'life0 self, data_ids: &'life1 [Uuid], timestamp: DateTime<Utc>, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

Update the last_accessed timestamp on the given Data records.

fn get_latest_pipeline_status<'life0, 'life1, 'async_trait>( &'life0 self, pipeline_name: &'life1 str, dataset_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<PipelineRunStatus>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

Get the latest pipeline run status for a (pipeline_name, dataset_id) pair.

impl<'c> IntoSchemaManagerConnection<'c> for &'c DatabaseConnection

fn into_schema_manager_connection(self) -> SchemaManagerConnection<'c>

impl NotebookDb for DatabaseConnection

fn list_by_owner<'life0, 'async_trait>( &'life0 self, owner_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Vec<Notebook>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Return all notebooks owned by owner_id, ordered by created_at asc.

fn create<'life0, 'async_trait>( &'life0 self, owner_id: Uuid, name: String, cells: Value, deletable: bool, ) -> Pin<Box<dyn Future<Output = Result<Notebook, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Insert a new notebook row and return it.

fn create_seeded<'life0, 'async_trait>( &'life0 self, id: Uuid, owner_id: Uuid, name: String, cells: Value, deletable: bool, ) -> Pin<Box<dyn Future<Output = Result<Notebook, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Insert a notebook with a caller-supplied id (used by the tutorial seeder to guarantee deterministic UUID5 ids across SDK restarts).

fn get_by_id_and_owner<'life0, 'async_trait>( &'life0 self, id: Uuid, owner_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<Option<Notebook>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Fetch a notebook by id, scoped to the owner.

fn update<'life0, 'async_trait>( &'life0 self, id: Uuid, owner_id: Uuid, patch: NotebookUpdatePatch, ) -> Pin<Box<dyn Future<Output = Result<Option<Notebook>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Apply a partial update. Returns the updated row or None when not found (ownership check included).

fn delete<'life0, 'async_trait>( &'life0 self, id: Uuid, owner_id: Uuid, ) -> Pin<Box<dyn Future<Output = Result<bool, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Delete a notebook. Returns true if a row was actually removed.

impl SearchHistoryDb for DatabaseConnection

fn log_query<'life0, 'life1, 'life2, 'async_trait>( &'life0 self, query_text: &'life1 str, query_type: &'life2 str, user_id: Option<Uuid>, ) -> Pin<Box<dyn Future<Output = Result<Uuid, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait, 'life2: 'async_trait,

fn log_result<'life0, 'life1, 'async_trait>( &'life0 self, query_id: Uuid, serialized_result: &'life1 str, user_id: Option<Uuid>, ) -> Pin<Box<dyn Future<Output = Result<Uuid, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

fn get_history<'life0, 'async_trait>( &'life0 self, user_id: Option<Uuid>, limit: Option<usize>, ) -> Pin<Box<dyn Future<Output = Result<Vec<SearchHistoryEntry>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

impl SessionLifecycleDb for DatabaseConnection

fn ensure_and_touch_session<'life0, 'life1, 'async_trait>( &'life0 self, session_id: &'life1 str, user_id: Uuid, dataset_id: Option<Uuid>, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

Upsert a session row, bumping last_activity_at if the row is already running. Mirrors metrics.py:62-130.

fn accumulate_usage<'life0, 'life1, 'life2, 'async_trait>( &'life0 self, session_id: &'life1 str, user_id: Uuid, model: Option<&'life2 str>, tokens_in: i64, tokens_out: i64, cost_usd: f64, errored: bool, ) -> Pin<Box<dyn Future<Output = Result<(), DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait, 'life2: 'async_trait,

Atomically add usage counters to the session row + per-model row. Mirrors metrics.py:133-241.

fn get_session_row<'life0, 'life1, 'life2, 'async_trait>( &'life0 self, session_id: &'life1 str, user_id: Uuid, permitted_dataset_ids: &'life2 [Uuid], prefer_other_owner: bool, ) -> Pin<Box<dyn Future<Output = Result<Option<SessionRowWithStatus>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait, 'life2: 'async_trait,

Visibility-checked single-row read. Mirrors metrics.py:295-333.

fn list_session_rows<'life0, 'async_trait>( &'life0 self, filters: SessionListFilters, ) -> Pin<Box<dyn Future<Output = Result<SessionListPage, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

Paginated list with effective_status filter support. Mirrors metrics.py:365-438.

fn aggregate_stats<'life0, 'life1, 'async_trait>( &'life0 self, user_id: Uuid, permitted_dataset_ids: &'life1 [Uuid], since: Option<DateTime<Utc>>, ) -> Pin<Box<dyn Future<Output = Result<SessionStats, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

Dashboard counters for GET /sessions/stats. Mirrors get_sessions_router.py:112-196.

fn cost_by_model<'life0, 'life1, 'async_trait>( &'life0 self, user_id: Uuid, permitted_dataset_ids: &'life1 [Uuid], since: Option<DateTime<Utc>>, ) -> Pin<Box<dyn Future<Output = Result<Vec<CostByModelRow>, DatabaseError>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait, 'life1: 'async_trait,

Per-model attribution for GET /sessions/cost-by-model. Mirrors get_sessions_router.py:198-252.

impl StreamTrait for DatabaseConnection

type Stream<'a> = QueryStream

Create a stream for the QueryResult

fn stream<'a>( &'a self, stmt: Statement, ) -> Pin<Box<dyn Future<Output = Result<<DatabaseConnection as StreamTrait>::Stream<'a>, DbErr>> + Send + 'a>>

Execute a Statement and return a stream of results

impl TransactionTrait for DatabaseConnection

fn transaction<'life0, 'async_trait, F, T, E>( &'life0 self, _callback: F, ) -> Pin<Box<dyn Future<Output = Result<T, TransactionError<E>>> + Send + 'async_trait>>

where 'life0: 'async_trait, F: for<'c> FnOnce(&'c DatabaseTransaction) -> Pin<Box<dyn Future<Output = Result<T, E>> + Send + 'c>> + Send + 'async_trait, T: Send + 'async_trait, E: Display + Debug + Send + 'async_trait, DatabaseConnection: 'async_trait,

Execute the function inside a transaction. If the function returns an error, the transaction will be rolled back. If it does not return an error, the transaction will be committed.

fn transaction_with_config<'life0, 'async_trait, F, T, E>( &'life0 self, _callback: F, _isolation_level: Option<IsolationLevel>, _access_mode: Option<AccessMode>, ) -> Pin<Box<dyn Future<Output = Result<T, TransactionError<E>>> + Send + 'async_trait>>

where 'life0: 'async_trait, F: for<'c> FnOnce(&'c DatabaseTransaction) -> Pin<Box<dyn Future<Output = Result<T, E>> + Send + 'c>> + Send + 'async_trait, T: Send + 'async_trait, E: Display + Debug + Send + 'async_trait, DatabaseConnection: 'async_trait,

Execute the function inside a transaction. If the function returns an error, the transaction will be rolled back. If it does not return an error, the transaction will be committed.

fn begin<'life0, 'async_trait>( &'life0 self, ) -> Pin<Box<dyn Future<Output = Result<DatabaseTransaction, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, DatabaseConnection: 'async_trait,

Execute SQL BEGIN transaction. Returns a Transaction that can be committed or rolled back

fn begin_with_config<'life0, 'async_trait>( &'life0 self, _isolation_level: Option<IsolationLevel>, _access_mode: Option<AccessMode>, ) -> Pin<Box<dyn Future<Output = Result<DatabaseTransaction, DbErr>> + Send + 'async_trait>>

where 'life0: 'async_trait, DatabaseConnection: 'async_trait,

Execute SQL BEGIN transaction with isolation level and/or access mode. Returns a Transaction that can be committed or rolled back