Trait spacetimedb_vm::expr::SourceProvider

pub trait SourceProvider<'a> {
    type Source: 'a + IntoIterator<Item = RelValue<'a>>;

    // Required method
    fn take_source(&mut self, id: SourceId) -> Option<Self::Source>;
}

Types that relate SourceIds to their in-memory tables.

Rather than embedding tables in query plans, we store a SourceExpr::InMemory, which contains the information necessary for optimization along with a SourceId. Query execution then executes the plan, and when it encounters a SourceExpr::InMemory, retrieves the Self::Source table from the corresponding provider. This allows query plans to be re-used, though each execution might require a new provider.

An in-memory table Self::Source is a type capable of producing [RelValue<'a>]s. The general form of this is Iterator<Item = RelValue<'a>>. Depending on the situation, this could be e.g.,

• MemTable, producing RelValue::Projection,
• &'a [ProductValue] producing RelValue::ProjRef.

Required Associated Types

type Source: 'a + IntoIterator<Item = RelValue<'a>>

The type of in-memory tables that this provider uses.

Required Methods

fn take_source(&mut self, id: SourceId) -> Option<Self::Source>

Retrieve the Self::Source associated with id, if any.

Taking the same id a second time may or may not yield the same source. Callers should not assume that a generic provider will yield it more than once. This means that a query plan may not include multiple references to the same SourceId.

Implementations are also not obligated to inspect id, e.g., if there’s only one option.

Implementations on Foreign Types

impl<'a, I: 'a + IntoIterator<Item = RelValue<'a>>> SourceProvider<'a> for Option<I>

type Source = I

fn take_source(&mut self, _: SourceId) -> Option<Self::Source>

Implementors

impl<'a> SourceProvider<'a> for NoInMemUsed

type Source = Empty<RelValue<'a>>

impl<'a, I: 'a + IntoIterator<Item = RelValue<'a>>, F: FnMut(SourceId) -> Option<I>> SourceProvider<'a> for F

type Source = I

impl<'a, T: 'a + IntoIterator<Item = RelValue<'a>>, const N: usize> SourceProvider<'a> for SourceSet<T, N>

type Source = T