Module driver 

Database driver traits and capability descriptions. Database driver interface for Toasty.

This module defines the traits and types that database drivers must implement to integrate with the Toasty query engine. The two core traits are [Driver] (factory for connections and schema operations) and Connection (executes operations against a live database session).

The query planner inspects [Capability] to decide which [Operation] variants to emit. SQL-based drivers receive [Operation::QuerySql] and [Operation::Insert], while key-value drivers (e.g., DynamoDB) receive [Operation::GetByKey], [Operation::QueryPk], etc. The [SchemaMutations] sub-struct (Capability::schema_mutations) describes what the database can do to its own schema — for example, whether ALTER COLUMN can change a column’s type — and the migration generator consults it to decide between an in-place alter and a table rebuild.

Architecture

Query Engine  ──▶  Operation  ──▶  Connection::exec()  ──▶  ExecResponse
                       ▲
                       │
              Driver::capability()

Error classification

The pool and the engine branch on the error variant returned from Connection::exec and Connection::ping. Drivers MUST cooperate with those branches:

• A connection-level fault (closed socket, broken pipe, protocol error, end-of-stream during handshake) MUST be classified as crate::Error::connection_lost. The pool uses that signal to evict the slot and to wake the background sweep, which then pings the remaining idle connections and drops any that also fail. Any other error variant for the same condition leaks a dead connection back into the pool.

• A retryable transaction conflict (PostgreSQL SQLSTATE 40001, MySQL error 1213) SHOULD be classified as crate::Error::serialization_failure. The engine does not retry automatically; the classification is propagated to user code so the caller can decide.

• A write attempted against a read-only session (PostgreSQL 25006, MySQL 1792) SHOULD be classified as crate::Error::read_only_transaction.

Other backend errors are typically wrapped with crate::Error::driver_operation_failed.

Re-exports

pub use operation::IsolationLevel;

pub use operation::Operation;

Modules

operation

Database operations dispatched to drivers.

Structs

Capability

Describes what a database driver supports.

ExecResponse

The result of a database operation.

SchemaMutations

The database’s capabilities to mutate the schema (tables, columns, indices).

StorageTypes

Maps application-level types to the concrete database column types used for storage.

Enums

Rows

The payload of an ExecResponse.

Traits

Connection

A live database session that can execute Operations.

Driver

Factory for database connections and provider of driver-level metadata.