Documentation ¶
Overview ¶
Package boltdb provides utilities for building BoltDB-based projections.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func New ¶
func New( db *bolt.DB, h MessageHandler, ) dogma.ProjectionMessageHandler
New returns a new projection message handler that uses the given database.
Types ¶
type MessageHandler ¶
type MessageHandler interface { // Configure produces a configuration for this handler by calling methods on // the configurer c. // // The implementation MUST allow for multiple calls to Configure(). Each // call SHOULD produce the same configuration. // // The engine MUST call Configure() before calling HandleEvent(). It is // RECOMMENDED that the engine only call Configure() once per handler. Configure(c dogma.ProjectionConfigurer) // HandleEvent updates the projection to reflect the occurrence of an event. // // Changes to the projection state MUST be performed within the supplied // transaction. // // If nil is returned, the projection state has been persisted successfully. // // If an error is returned, the projection SHOULD be left in the state it // was before HandleEvent() was called. // // The engine SHOULD provide "at-least-once" delivery guarantees to the // handler. That is, the engine should call HandleEvent() with the same // event message until a nil error is returned. // // The engine MAY provide guarantees about the order in which event messages // will be passed to HandleEvent(), however in the interest of engine // portability the implementation SHOULD NOT assume that HandleEvent() will // be called with events in the same order that they were recorded. // // The supplied context parameter SHOULD have a deadline. The implementation // SHOULD NOT impose its own deadline. Instead a suitable timeout duration // can be suggested to the engine via the handler's TimeoutHint() method. // // The engine MUST NOT call HandleEvent() with any message of a type that // has not been configured for consumption by a prior call to Configure(). // If any such message is passed, the implementation MUST panic with the // UnexpectedMessage value. // // The engine MAY call HandleEvent() from multiple goroutines concurrently. HandleEvent(ctx context.Context, tx *bolt.Tx, s dogma.ProjectionEventScope, m dogma.Message) error // TimeoutHint returns a duration that is suitable for computing a deadline // for the handling of the given message by this handler. // // The hint SHOULD be as short as possible. The implementation MAY return a // zero-value to indicate that no hint can be made. // // The engine SHOULD use a duration as close as possible to the hint. Use of // a duration shorter than the hint is NOT RECOMMENDED, as this will likely // lead to repeated message handling failures. TimeoutHint(m dogma.Message) time.Duration // Compact reduces the size of the projection's data. // // The implementation SHOULD attempt to decrease the size of the // projection's data by whatever means available. For example, it may delete // any unused data, or collapse multiple data sets into one. // // The context MAY have a deadline. The implementation SHOULD compact data // using multiple small transactions, such that if the deadline is reached a // future call to Compact() does not need to compact the same data. // // The engine SHOULD call Compact() repeatedly throughout the lifetime of // the projection. The precise scheduling of calls to Compact() are // engine-defined. It MAY be called concurrently with any other method. Compact(ctx context.Context, db *bolt.DB, s dogma.ProjectionCompactScope) error }
MessageHandler is a specialization of dogma.ProjectionMessageHandler that persists to a BoltDB database.
type NoCompactBehavior ¶ added in v0.5.1
type NoCompactBehavior struct{}
NoCompactBehavior can be embedded in MessageHandler implementations to indicate that the projection does not require its data to be compacted.
It provides an implementation of MessageHandler.Compact() that always returns a nil error.
func (NoCompactBehavior) Compact ¶ added in v0.5.1
func (NoCompactBehavior) Compact( ctx context.Context, db *bolt.DB, s dogma.ProjectionCompactScope, ) error
Compact returns nil.
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