Struct QueryContext 

pub struct QueryContext<'a> { /* private fields */ }

Context provided to queries during execution.

Use this to access dependencies via query().

Implementations

impl<'a> QueryContext<'a>

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

Query a dependency.

The dependency is automatically tracked for invalidation.

Example

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

pub fn asset<K: AssetKey>( &mut self, key: &K, ) -> Result<LoadingState<Arc<K::Asset>>, QueryError>

Access an asset, tracking it as a dependency.

Returns LoadingState<Arc<K::Asset>>:

• LoadingState::Loading if the asset is still being loaded
• LoadingState::Ready(value) if the asset is available

Example

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

Errors

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

pub fn list_queries<Q: Query>(&mut 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(ctx: &mut QueryContext) -> Result<Vec<i32>, QueryError> {
    let queries = ctx.list_queries::<MyQuery>();
    let mut results = Vec::new();
    for q in queries {
        results.push(*ctx.query(q)?);
    }
    Ok(results)
}

pub fn list_asset_keys<K: AssetKey>(&mut 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 ctx.asset() for that)

Example

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