Struct Projection 

pub struct Projection<E: Executor, P: Default + 'static> { /* private fields */ }

Projection for loading aggregate state from events.

Combines event handlers to rebuild aggregate state by replaying events. Supports snapshots for performance optimization.

Example

let result = Projection::<_, AccountView>::new::<Account>("account-123")
    .handler(account_opened)
    .handler(money_deposited)
    .data(app_config)
    .execute(&executor)
    .await?;

Implementations

impl<E: Executor, P: Snapshot<E> + Default + 'static> Projection<E, P>

pub fn new<A: Aggregator>(id: impl Into<String>) -> Projection<E, P>

where P: Snapshot<E> + Default,

Creates a builder for loading aggregate state.

This consumes the projection and returns a [LoadBuilder] configured to load the state for the specified aggregate.

Type Parameters

• A: The aggregate type to load

pub fn ids<A: Aggregator>(ids: Vec<impl Into<String>>) -> Projection<E, P>

where P: Snapshot<E> + Default,

Creates a builder for loading aggregate state.

This consumes the projection and returns a [LoadBuilder] configured to load the state for the specified aggregate.

Type Parameters

• A: The aggregate type to load

pub fn revision(self, value: u16) -> Self

Sets the snapshot revision.

Changing the revision invalidates existing snapshots, forcing a full rebuild.

pub fn safety_check(self) -> Self

Enables safety checks for unhandled events.

When enabled, execution fails if an event is encountered without a handler.

pub fn handler<H: Handler<P> + 'static>(self, h: H) -> Self

Registers an event handler with this projection.

Panics

Panics if a handler for the same event type is already registered.

pub fn skip<EV: AggregatorEvent + Send + Sync + 'static>(self) -> Self

Registers a skip handler with this projection.

Panics

Panics if a handler for the same event type is already registered.

pub fn data<D: Send + Sync + 'static>(self, v: D) -> Self

Adds shared data to the load context.

Data added here is accessible in handlers via the context.

pub fn aggregator<A: Aggregator>(self, id: impl Into<String>) -> Self

Adds a related aggregate to load events from.

Use this when the projection needs events from multiple aggregates.

pub fn aggregator_raw( self, aggregator_type: impl Into<String>, id: impl Into<String>, ) -> Self

Adds a related aggregate to load events from.

Use this when the projection needs events from multiple aggregates.

pub async fn execute(&self, executor: &E) -> Result<Option<P>>

Executes the load operation, returning the rebuilt state.

Returns None if no events exist for the aggregate. Returns Err if there are too many events to process in one batch.