Struct arrow::json::reader::Decoder

pub struct Decoder { /* private fields */ }

JSON values to Arrow record batch decoder.

A Decoder decodes arbitrary streams of serde_json::Values and converts them to RecordBatches. To decode JSON formatted files, see Reader.

Examples

use arrow::json::reader::{Decoder, DecoderOptions, ValueIter, infer_json_schema};
use std::fs::File;
use std::io::{BufReader, Seek, SeekFrom};
use std::sync::Arc;

let mut reader =
    BufReader::new(File::open("test/data/mixed_arrays.json").unwrap());
let inferred_schema = infer_json_schema(&mut reader, None).unwrap();
let options = DecoderOptions::new()
    .with_batch_size(1024);
let decoder = Decoder::new(Arc::new(inferred_schema), options);

// seek back to start so that the original file is usable again
reader.seek(SeekFrom::Start(0)).unwrap();
let mut value_reader = ValueIter::new(&mut reader, None);
let batch = decoder.next_batch(&mut value_reader).unwrap().unwrap();
assert_eq!(4, batch.num_rows());
assert_eq!(4, batch.num_columns());

Implementations

impl Decoder

pub fn new(schema: SchemaRef, options: DecoderOptions) -> Self

Create a new JSON decoder from some value that implements an iterator over serde_json::Values (aka implements the Iterator<Item=Result<Value>> trait).

pub fn schema(&self) -> SchemaRef

Returns the schema of the reader, useful for getting the schema without reading record batches

pub fn next_batch<I>(&self, value_iter: &mut I) -> Result<Option<RecordBatch>> where
    I: Iterator<Item = Result<Value>>, 

Read the next batch of serde_json::Value records from the interator into a RecordBatch.

Returns None if the input iterator is exhausted.

Trait Implementations

impl Debug for Decoder

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

Formats the value using the given formatter.