org.apache.drill.exec.vector.accessor

Interface VariantWriter

All Superinterfaces:

ColumnWriter

All Known Implementing Classes:

UnionWriterImpl

public interface VariantWriter
extends ColumnWriter

Writer for a Drill "union vector." The union vector is presented as a writer over a set of variants. In the old Visual Basic world, "the Variant data type is a tagged union that can be used to represent any other data type." The term is used here to avoid confusion with the "union operator" which is something entirely different.

At write time, the set of possible types is expanded upon the first write to each type. A request to obtain a writer for type will create the underlying storage vector if needed, then return a write of the proper type. Note that unlike most other writers, the caller is required to call the #scalar(MinorType) method for each value so that this writer knows which type of value is to be stored.

Alternatively, the client can cache a writer by calling #memberWriter(MinorType) to retrieve a writer (without setting the type for a row), then calling the set method on that writer for each row, and calling #setType(MinorType) for each row.

This writer acts as somewhat like a map: it allows access to type-specific writers.

Although the union and list vectors 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.

See Also:

VariantReader}

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static interface	VariantWriter.VariantWriterListener

Method Summary

Modifier and Type	Method and Description
ObjectWriter	addMember(ColumnMetadata schema)
ObjectWriter	addMember(TypeProtos.MinorType type)
ArrayWriter	array()
boolean	hasType(TypeProtos.MinorType type) Determine if the union vector has materialized storage for the given type.
ObjectWriter	member(TypeProtos.MinorType type) Set the type of the present value and get the writer for that type.
ObjectWriter	memberWriter(TypeProtos.MinorType type) Create or retrieve a writer for the given type.
ScalarWriter	scalar(TypeProtos.MinorType type)
void	setType(TypeProtos.MinorType type) Explicitly set the type of the present value.
int	size() Returns the number of types in the variant.
TupleWriter	tuple()
VariantMetadata	variantSchema() Metadata description of the variant that includes the set of types, along with extended properties of the types such as expected allocations sizes, expected array cardinality, etc.

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

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

Method Detail

variantSchema

VariantMetadata variantSchema()

Metadata description of the variant that includes the set of types, along with extended properties of the types such as expected allocations sizes, expected array cardinality, etc.

Returns:

metadata for the variant

size

int size()

Returns the number of types in the variant. Some implementations (such as lists) impart special meaning to a variant with a single type.

Returns:

number of types in the variant

hasType

boolean hasType(TypeProtos.MinorType type)

Determine if the union vector has materialized storage for the given type. (The storage will be created as needed during writing.)

Parameters:

type - data type

Returns:

true if a value of the given type has been written and storage allocated (or storage was allocated implicitly), false otherwise

addMember

ObjectWriter addMember(TypeProtos.MinorType type)

addMember

ObjectWriter addMember(ColumnMetadata schema)

memberWriter

ObjectWriter memberWriter(TypeProtos.MinorType type)

Create or retrieve a writer for the given type. Use this form when caching writers. This form does not set the type of the current row; call #setType(MinorType) per row when the writers are cached. This method can be called at any time as it does not depend on an active batch.

Parameters:

type - the type of the writer to cache

Returns:

the writer for that type without setting the type of the current row.

setType

void setType(TypeProtos.MinorType type)

Explicitly set the type of the present value. Use this when the writers are cached. The writer must already exist.

Parameters:

type - type to set for the current row

member

ObjectWriter member(TypeProtos.MinorType type)

Set the type of the present value and get the writer for that type. Available only when a batch is active. Use this form to declare the type of the current row, and retrieve a writer for that value.

Parameters:

type - type to set for the current row

Returns:

writer for the type just set

scalar

ScalarWriter scalar(TypeProtos.MinorType type)

tuple

TupleWriter tuple()

array

ArrayWriter array()