Package org.apache.druid.frame.read

Class FrameReader

java.lang.Object

org.apache.druid.frame.read.FrameReader

public class FrameReader
extends Object

Embeds the logic to read frames with a given RowSignature.

Stateless and immutable.

Method Summary

Modifier and Type	Method	Description
ColumnCapabilities	columnCapabilities(Frame frame, String columnName)	Returns capabilities for a particular column in a particular frame.
static FrameReader	create(RowSignature signature)	Create a reader for frames with a given RowSignature.
FrameComparisonWidget	makeComparisonWidget(Frame frame, List<KeyColumn> keyColumns)	Create a FrameComparisonWidget for the given frame.
CursorFactory	makeCursorFactory(Frame frame)	Create a CursorFactory for the given frame.
RowSignature	signature()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

create

public static FrameReader create(RowSignature signature)

Create a reader for frames with a given RowSignature. The signature must exactly match the frames to be read, or else behavior is undefined. If the columnType is null, we store the data as ColumnType.NESTED_DATA. This can be done if we know that the data that we receive can be serded generically using the nested data. It is currently used in the brokers to store the data with unknown types into frames.

Parameters:

signature - signature used to generate the reader

signature

public RowSignature signature()

columnCapabilities

@Nullable
public ColumnCapabilities columnCapabilities(Frame frame,
                                             String columnName)

Returns capabilities for a particular column in a particular frame.

Preferred over RowSignature.getColumnCapabilities(String) when reading a particular frame, because this method has more insight into what's actually going on with that specific frame (nulls, multivalue, etc). The RowSignature version is based solely on type.

makeCursorFactory

public CursorFactory makeCursorFactory(Frame frame)

Create a CursorFactory for the given frame.

makeComparisonWidget

public FrameComparisonWidget makeComparisonWidget(Frame frame,
                                                  List<KeyColumn> keyColumns)

Create a FrameComparisonWidget for the given frame.

Only possible for frames of type FrameType.ROW_BASED. The provided sortColumns must be a prefix of signature().