Struct ArrowReader

pub struct ArrowReader {
    len: usize,
    readers: Vec<ColReader>,
}

Type that can read out of an arrow::array::StructArray and into a Row, given a RelationDesc.

The inverse of a crate::builder::ArrowBuilder.

Note: When creating an ArrowReader we perform a “one-time downcast” of the children Arrays from the StructArray, into enum ColReaders. This is a much more verbose approach than the alternative of downcasting from a dyn arrow::array::Array every time we read a Row, but it is much more performant.

Fields

len: usize

readers: Vec<ColReader>

Implementations

impl ArrowReader

pub fn new(desc: &RelationDesc, array: StructArray) -> Result<Self, Error>

Create an ArrowReader validating that the provided RelationDesc and StructArray have a matching schema.

The RelationDesc and StructArray need to uphold the following to be a valid pair:

• Same number of columns.
• Columns of all the same name.
• Columns of compatible types.

TODO(cf2): Relax some of these restrictions by allowing users to map column names, omit columns, perform some lightweight casting, and matching not on column name but column position. TODO(cf2): Allow specifying an optional arrow::Schema for extra metadata.

pub fn read(&self, idx: usize, row: &mut Row) -> Result<(), Error>

Read the value at idx into the provided Row.

pub fn read_all(&self, rows: &mut Vec<Row>) -> Result<usize, Error>

Read all of the values in this ArrowReader into rows.