org.apache.drill.exec.vector.accessor

Interface ArrayWriter

All Superinterfaces:

ColumnWriter

All Known Subinterfaces:

DictWriter

All Known Implementing Classes:

AbstractArrayWriter, AbstractArrayWriter.BaseArrayWriter, DummyArrayWriter, DummyDictWriter, ListWriterImpl, ObjectArrayWriter, ObjectDictWriter, RepeatedListWriter, ScalarArrayWriter

public interface ArrayWriter
extends ColumnWriter

Writer for values into an array. Array writes are write-once, sequential: each call to a setFoo() method writes a value and advances the array index.

The array writer represents a Drill repeated type, including repeated maps. The array writer also represents the Drill list and repeated list types as follows:

• A repeated scalar type is presented as an array writer with scalar entries. As a convenience, writing to the scalar automatically advances the current array write position, since exactly one item can be written per array entry.
• A repeated map type is presented as an array writer with tuple entries. The client must advance the array write position explicitly since a tuple can have any number of entries and the array writer cannot determine when a value is complete.
• A list type is presented as an array of variant entries. The client must explicitly advance the array position.
• A repeated list type is presented as an array of arrays of variants. The client advances the array position of both lists.
• Lists of repeated lists have three levels of arrays, repeated lists of repeated lists have four levels of arrays, and so on.

Although the list vector supports a union of any Drill type, the only sane combinations are:

• One of a (single or repeated) (map or list), or
• One or more scalar type.

If a particular array has only one type (single/repeated map/list), then, for convenience, the caller can directly request a writer of that type without having to first retrieve the variant (although the indirect route is, of course, available.)

See Also:

ArrayReader

Method Summary

Modifier and Type	Method and Description
ArrayWriter	array()
DictWriter	dict()
ObjectWriter	entry() The object type of the list entry.
ObjectType	entryType() Return a generic object writer for the array entry.
void	save() When the array contains a tuple or an array, call save() after each array value.
ScalarWriter	scalar()
void	setNull(boolean isNull)
int	size() Number of elements written thus far to the array.
TupleWriter	tuple()
VariantWriter	variant()

Methods inherited from interface org.apache.drill.exec.vector.accessor.ColumnWriter

copy, isProjected, nullable, schema, setNull, setObject, type

Method Detail

size

int size()

Number of elements written thus far to the array.

Returns:

the number of elements

entryType

ObjectType entryType()

Return a generic object writer for the array entry.

Returns:

generic object reader

setNull

void setNull(boolean isNull)

entry

ObjectWriter entry()

The object type of the list entry. All entries have the same type.

Returns:

the object type of each entry

scalar

ScalarWriter scalar()

tuple

TupleWriter tuple()

array

ArrayWriter array()

variant

VariantWriter variant()

dict

DictWriter dict()

save

void save()

When the array contains a tuple or an array, call save() after each array value. Not necessary when writing scalars; each set operation calls save automatically.