Struct ExecutionState 

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

A handle on a database that may be in the process of running a rule.

An ExecutionState grants immutable access to the (much of) the database, and also provides a limited API to mutate database contents.

A few important notes:

Some tables may be missing

Callers external to this crate cannot construct an ExecutionState directly. Depending on the context, some tables may not be available. In particular, when running crate::Table::merge operations, only a table’s read-side dependencies are available for reading (sim. for writing). This allows tables that do not need access to one another to be merged in parallel.

When executing a rule, ExecutionState has access to all tables.

Limited Mutability

Callers can only stage insertsions and deletions to tables. These changes are not applied until the next call to merge on the underlying table.

Predicted Values

ExecutionStates provide a means of synchronizing the results of a pending write across different executions of a rule. This is particularly important in the case where the result of an operation (such as “lookup or insert new id” operatiosn) is a fresh id. A common ExecutionState ensures that future lookups will see the same id (even across calls to ExecutionState::clone).

Implementations

impl<'a> ExecutionState<'a>

pub fn stage_insert(&mut self, table: TableId, row: &[Value])

Stage an insertion of the given row into table.

If you are using egglog, consider using egglog_bridge::TableAction.

pub fn stage_remove(&mut self, table: TableId, key: &[Value])

Stage a removal of the given row from table if it is present.

If you are using egglog, consider using egglog_bridge::TableAction.

pub fn call_external_func( &mut self, func: ExternalFunctionId, args: &[Value], ) -> Option<Value>

Call an external function.

pub fn inc_counter(&self, ctr: CounterId) -> usize

pub fn read_counter(&self, ctr: CounterId) -> usize

pub fn get_table(&self, table: TableId) -> &'a WrappedTable

Get an immutable reference to the table with id table. Dangerous: Reading from a table during action execution may break the semi-naive evaluation

pub fn base_values(&self) -> &BaseValues

pub fn container_values(&self) -> &'a ContainerValues

pub fn predict_val( &mut self, table: TableId, key: &[Value], vals: impl ExactSizeIterator<Item = MergeVal>, ) -> Pooled<Vec<Value>>

Get the current value for a given key in table, or otherwise insert the unique next value.

Insertions into tables are not performed immediately, but rules and merge functions sometimes need to get the result of an insertion. For such cases, executions keep a cache of “predicted” values for a given mapping that manage the insertions, etc.

If you are using egglog, consider using egglog_bridge::TableAction.

pub fn predict_col( &mut self, table: TableId, key: &[Value], vals: impl ExactSizeIterator<Item = MergeVal>, col: ColumnId, ) -> Value

A variant of ExecutionState::predict_val that avoids materializing the full row, and instead only returns the value in the given column.

Trait Implementations

impl Clone for ExecutionState<'_>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.