Struct MetadataTransformer 

pub struct MetadataTransformer { /* private fields */ }

Set / merge fixed metadata onto every document. Use to tag a batch with provenance (source = "kb-2026-05"), pipeline stage, etc.

Existing keys are overwritten by default; use MetadataTransformer::merge_only_missing to keep existing values.

Implementations

impl MetadataTransformer

pub fn new() -> Self

Empty transformer — add fields with MetadataTransformer::set.

pub fn from_map(fields: HashMap<String, Value>) -> Self

Construct from a map. Keys are merged into every document.

pub fn set(self, key: impl Into<String>, value: impl Into<Value>) -> Self

Add a single key / value.

pub fn merge_only_missing(self) -> Self

Don’t overwrite keys the doc already has.

pub fn apply(&self, docs: Vec<Document>) -> Vec<Document>

Pure form.

Trait Implementations

impl Clone for MetadataTransformer

fn clone(&self) -> MetadataTransformer

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for MetadataTransformer

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for MetadataTransformer

fn default() -> MetadataTransformer

Returns the “default value” for a type.

impl Runnable<Vec<Document>, Vec<Document>> for MetadataTransformer

fn invoke<'life0, 'async_trait>( &'life0 self, input: Vec<Document>, __arg2: RunnableConfig, ) -> Pin<Box<dyn Future<Output = Result<Vec<Document>>> + Send + 'async_trait>>

where Self: 'async_trait, 'life0: 'async_trait,

One-shot invocation. The hot path.

fn name(&self) -> &str

Friendly name for telemetry / introspection.

fn batch<'life0, 'async_trait>( &'life0 self, inputs: Vec<I>, config: RunnableConfig, ) -> Pin<Box<dyn Future<Output = Result<Vec<O>, CognisError>> + Send + 'async_trait>>

where 'life0: 'async_trait, I: 'static, O: 'static, Self: Sized + Sync + 'async_trait,

Run multiple inputs in parallel. Defaults to buffer_unordered honouring config.max_concurrency.

fn stream<'life0, 'async_trait>( &'life0 self, input: I, config: RunnableConfig, ) -> Pin<Box<dyn Future<Output = Result<RunnableStream<O>, CognisError>> + Send + 'async_trait>>

where 'life0: 'async_trait, Self: Sized + Sync + 'async_trait,

Stream the final output (chunks of O). Default emits one item via invoke — non-streaming runnables are correct without override.

fn stream_events<'life0, 'async_trait>( &'life0 self, input: I, config: RunnableConfig, ) -> Pin<Box<dyn Future<Output = Result<EventStream, CognisError>> + Send + 'async_trait>>

where 'life0: 'async_trait, I: Serialize, O: Serialize, Self: Sized + Sync + 'async_trait,

Stream structured events. Default emits OnStart + OnEnd around an invoke call. Graph engines override to surface per-node events.

fn input_schema(&self) -> Option<Value>

JSON Schema for the input type, if known.

fn output_schema(&self) -> Option<Value>

JSON Schema for the output type, if known.