Struct QueryContext

Source

pub struct QueryContext<'a, T: Tracer = NoopTracer> { /* private fields */ }

Expand description

Context provided to queries during execution.

Use this to access dependencies via query().

Implementations§

Source §

impl<'a, T: Tracer> QueryContext<'a, T>

Source

pub fn query<Q: Query>(&self, query: Q) -> Result<Arc<Q::Output>, QueryError>

Query a dependency.

The dependency is automatically tracked for invalidation.

§Example

fn query(self, db: &impl Db) -> Result<Self::Output, QueryError> {
    let dep_result = db.query(OtherQuery { id: self.id })?;
    Ok(process(&dep_result))
}

Source

pub fn asset<K: AssetKey>( &self, key: K, ) -> Result<AssetLoadingState<K>, QueryError>

Access an asset, tracking it as a dependency.

Returns AssetLoadingState<K>:

is_loading() if the asset is still being loaded
is_ready() if the asset is available

Use .suspend()? to convert to Result<Arc<K::Asset>, QueryError>, which returns Err(QueryError::Suspend { asset }) if still loading.

§Example

#[query]
fn process_file(db: &impl Db, path: FilePath) -> Result<Output, QueryError> {
    let content = db.asset(path)?.suspend()?;
    // Process content...
    Ok(output)
}

§Errors

Returns Err(QueryError::MissingDependency) if the asset was not found.

Source

pub fn list_queries<Q: Query>(&self) -> Vec<Q>

List all query instances of type Q that have been registered.

This method establishes a dependency on the “set” of queries of type Q. The calling query will be invalidated when:

A new query of type Q is first executed (added to set)

The calling query will NOT be invalidated when:

An individual query of type Q has its value change

§Example

#[query]
fn all_results(db: &impl Db) -> Result<Vec<i32>, QueryError> {
    let queries = db.list_queries::<MyQuery>();
    let mut results = Vec::new();
    for q in queries {
        results.push(*db.query(q)?);
    }
    Ok(results)
}

Source

pub fn list_asset_keys<K: AssetKey>(&self) -> Vec<K>

List all asset keys of type K that have been registered.

This method establishes a dependency on the “set” of asset keys of type K. The calling query will be invalidated when:

A new asset of type K is resolved for the first time (added to set)
An asset of type K is removed via remove_asset

The calling query will NOT be invalidated when:

An individual asset’s value changes (use db.asset() for that)

§Example

#[query]
fn all_configs(db: &impl Db) -> Result<Vec<String>, QueryError> {
    let keys = db.list_asset_keys::<ConfigFile>();
    let mut contents = Vec::new();
    for key in keys {
        let content = db.asset(&key)?.suspend()?;
        contents.push((*content).clone());
    }
    Ok(contents)
}