Struct ReaderBuilder

pub struct ReaderBuilder { /* private fields */ }

A builder for Reader and Decoder

Implementations

impl ReaderBuilder

pub fn new(schema: SchemaRef) -> Self

Create a new ReaderBuilder with the provided SchemaRef

This could be obtained using infer_json_schema if not known

Any columns not present in schema will be ignored, unless strict_mode is set to true. In this case, an error is returned when a column is missing from schema.

pub fn new_with_field(field: impl Into<FieldRef>) -> Self

Create a new ReaderBuilder that will parse JSON values of field.data_type()

Unlike ReaderBuilder::new this does not require the root of the JSON data to be an object, i.e. {..}, allowing for parsing of any valid JSON value(s)

// Root of JSON schema is a numeric type
let data = "1\n2\n3\n";
let field = Arc::new(Field::new("int", DataType::Int32, true));
let mut reader = ReaderBuilder::new_with_field(field.clone()).build(data.as_bytes()).unwrap();
let b = reader.next().unwrap().unwrap();
let values = b.column(0).as_primitive::<Int32Type>().values();
assert_eq!(values, &[1, 2, 3]);

// Root of JSON schema is a list type
let data = "[1, 2, 3, 4, 5, 6, 7]\n[1, 2, 3]";
let field = Field::new_list("int", field.clone(), true);
let mut reader = ReaderBuilder::new_with_field(field).build(data.as_bytes()).unwrap();
let b = reader.next().unwrap().unwrap();
let list = b.column(0).as_list::<i32>();

assert_eq!(list.offsets().as_ref(), &[0, 7, 10]);
let list_values = list.values().as_primitive::<Int32Type>();
assert_eq!(list_values.values(), &[1, 2, 3, 4, 5, 6, 7, 1, 2, 3]);

pub fn with_batch_size(self, batch_size: usize) -> Self

Sets the batch size in rows to read

pub fn with_coerce_primitive(self, coerce_primitive: bool) -> Self

Sets if the decoder should coerce primitive values (bool and number) into string when the Schema’s column is Utf8 or LargeUtf8.

pub fn with_strict_mode(self, strict_mode: bool) -> Self

Sets if the decoder should return an error if it encounters a column not present in schema. If struct_mode is ListOnly the value of strict_mode is effectively true. It is required for all fields of the struct to be in the list: without field names, there is no way to determine which field is missing.

pub fn with_struct_mode(self, struct_mode: StructMode) -> Self

Set the StructMode for the reader, which determines whether structs can be decoded from JSON as objects or lists. For more details refer to the enum documentation. Default is to use ObjectOnly.

pub fn build<R: BufRead>(self, reader: R) -> Result<Reader<R>, ArrowError>

Create a Reader with the provided BufRead

pub fn build_decoder(self) -> Result<Decoder, ArrowError>

Create a Decoder