Struct ProjectionMapper

pub struct ProjectionMapper {
    metadata: RegionMetadataRef,
    batch_indices: Vec<BatchIndex>,
    has_tags: bool,
    codec: Arc<dyn PrimaryKeyCodec>,
    output_schema: SchemaRef,
    column_ids: Vec<ColumnId>,
    batch_fields: Vec<(ColumnId, ConcreteDataType)>,
    is_empty_projection: bool,
}

Handles projection and converts a projected Batch to a projected RecordBatch.

Fields

metadata: RegionMetadataRef

Metadata of the region.

batch_indices: Vec<BatchIndex>

Maps column in RecordBatch to index in Batch.

has_tags: bool

Output record batch contains tags.

codec: Arc<dyn PrimaryKeyCodec>

Decoder for primary key.

output_schema: SchemaRef

Schema for converted RecordBatch.

column_ids: Vec<ColumnId>

Ids of columns to project. It keeps ids in the same order as the projection indices to build the mapper.

batch_fields: Vec<(ColumnId, ConcreteDataType)>

Ids and DataTypes of field columns in the Batch.

is_empty_projection: bool

true If the original projection is empty.

Implementations

impl ProjectionMapper

pub fn new( metadata: &RegionMetadataRef, projection: impl Iterator<Item = usize>, ) -> Result<ProjectionMapper>

Returns a new mapper with projection. If projection is empty, it outputs RecordBatch without any column but only a row count. SELECT COUNT(*) FROM table is an example that uses an empty projection. DataFusion accepts empty RecordBatch and only use its row count in this query.

pub fn all(metadata: &RegionMetadataRef) -> Result<ProjectionMapper>

Returns a new mapper without projection.

pub(crate) fn metadata(&self) -> &RegionMetadataRef

Returns the metadata that created the mapper.

pub(crate) fn column_ids(&self) -> &[ColumnId]

Returns ids of projected columns that we need to read from memtables and SSTs.

pub(crate) fn batch_fields(&self) -> &[(ColumnId, ConcreteDataType)]

Returns ids of fields in Batches the mapper expects to convert.

pub(crate) fn output_schema(&self) -> SchemaRef

Returns the schema of converted RecordBatch. This is the schema that the stream will output. This schema may contain less columns than ProjectionMapper::column_ids().

pub(crate) fn empty_record_batch(&self) -> RecordBatch

Returns an empty RecordBatch.

pub(crate) fn convert( &self, batch: &Batch, cache_strategy: &CacheStrategy, ) -> Result<RecordBatch>

Converts a Batch to a RecordBatch.

The batch must match the projection using to build the mapper.