org.apache.drill.exec.vector.accessor

Interface VariantReader

All Superinterfaces:

ColumnReader

All Known Implementing Classes:

UnionReaderImpl

public interface VariantReader
extends ColumnReader

Reader for a Drill "union vector." The union vector is presented as a reader 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 read time, the set of possible types is fixed. A request to obtain a reader for an unused type returns a null pointer.

This reader is essentially a map of types: it allows access to type-specific readers for the set of types supported in the current vector. A client checks the type of each value, then uses the proper type-specific reader to access that value.

See Also:

VariantWriter}

Method Summary

Modifier and Type	Method and Description
ArrayReader	array()
TypeProtos.MinorType	dataType() Return the data type of the current value.
boolean	hasType(TypeProtos.MinorType type) Determine if a given type is supported by the union vector for some value in the result set.
ObjectReader	member() Return the reader for the member type of the current row.
ObjectReader	member(TypeProtos.MinorType type) Return the member reader for the given type.
ScalarReader	scalar() Return the appropriate scalar reader for the current value.
ScalarReader	scalar(TypeProtos.MinorType type) Return the scalar reader for the given type member.
int	size()
TupleReader	tuple()
VariantMetadata	variantSchema()

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

getAsString, getObject, isNull, schema, type

Method Detail

variantSchema

VariantMetadata variantSchema()

size

int size()

hasType

boolean hasType(TypeProtos.MinorType type)

Determine if a given type is supported by the union vector for some value in the result set.

Parameters:

type - the Drill minor type to query

Returns:

true if a reader for the given type is available, false if a request for a reader of that type will return null.

member

ObjectReader member(TypeProtos.MinorType type)

Return the member reader for the given type. The type must be a member of the union. Allows caching readers across rows.

Parameters:

type - member type

Returns:

reader for that type

scalar

ScalarReader scalar(TypeProtos.MinorType type)

Return the scalar reader for the given type member. The type must be a member of the union. Allows caching readers across rows. Identical to:
>member(type).scalar()

Parameters:

type - member type

Returns:

scalar reader for that type

dataType

TypeProtos.MinorType dataType()

Return the data type of the current value. (What happens if the row is null, must it be a null of some type?)

Returns:

data type of the current data value

member

ObjectReader member()

Return the reader for the member type of the current row. Same as:
member(dataType())

Returns:

reader for the member type of the current row.

scalar

ScalarReader scalar()

Return the appropriate scalar reader for the current value.

Returns:

null if ColumnReader.isNull() returns true, else the equivalent of scalar( dataType() )

Throws:

IllegalStateException - if called for a variant that holds a tuple or an array

tuple

TupleReader tuple()

array

ArrayReader array()