Struct ProjectedFileReader 

pub struct ProjectedFileReader { /* private fields */ }

A projection-scoped reader for Lance files.

This reader fixes a base projection at construction time. All later reads must stay within that projection, which lets the reader load only the column metadata needed by the base projection when opening from a FileMetadataIndex. It intentionally does not expose APIs that require synchronous access to full file metadata.

Implementations

impl ProjectedFileReader

pub async fn try_open( scheduler: FileScheduler, base_projection: Option<ReaderProjection>, decoder_plugins: Arc<DecoderPlugins>, cache: &LanceCache, options: FileReaderOptions, ) -> Result<Self>

Opens a data reader backed by indexed column metadata.

base_projection must be a supported indexed projection. Reads that do not pass an explicit projection use this base projection.

pub async fn try_open_with_metadata_index( scheduler: Arc<dyn EncodingsIo>, path: Path, base_projection: Option<ReaderProjection>, decoder_plugins: Arc<DecoderPlugins>, metadata_index: Arc<FileMetadataIndex>, cache: &LanceCache, options: FileReaderOptions, ) -> Result<Self>

Opens a data reader from a previously loaded metadata index.

base_projection must be a supported indexed projection. Use Self::try_open_with_file_metadata when the default read should cover the whole file schema.

pub async fn try_open_with_file_metadata( scheduler: Arc<dyn EncodingsIo>, path: Path, base_projection: Option<ReaderProjection>, decoder_plugins: Arc<DecoderPlugins>, file_metadata: Arc<CachedFileMetadata>, cache: &LanceCache, options: FileReaderOptions, ) -> Result<Self>

pub fn supports_projection( projection: &ReaderProjection, version: LanceFileVersion, ) -> bool

Returns whether a projection can be served by indexed column metadata.

pub fn with_scheduler(&self, scheduler: Arc<dyn EncodingsIo>) -> Self

Returns a clone of this reader using a different scheduler.

pub fn version(&self) -> LanceFileVersion

Returns the Lance file version.

pub fn num_rows(&self) -> u64

Returns the number of rows in the file.

pub fn schema(&self) -> &Arc<Schema>

Returns the file schema visible to this reader.

pub fn file_statistics(&self) -> Option<FileStatistics>

Returns file statistics when this reader has full file metadata.

pub async fn read_global_buffer(&self, index: u32) -> Result<Bytes>

Reads a global buffer by index.

pub async fn read_tasks( &self, params: ReadBatchParams, batch_size: u32, projection: Option<ReaderProjection>, filter: FilterExpression, ) -> Result<Pin<Box<dyn Stream<Item = ReadBatchTask> + Send>>>

Creates a stream of read tasks for the requested rows and projection.

Trait Implementations

impl Clone for ProjectedFileReader

fn clone(&self) -> ProjectedFileReader

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ProjectedFileReader

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

Formats the value using the given formatter.