Package org.apache.druid.segment

Interface VirtualColumn

All Superinterfaces:

Cacheable

All Known Implementing Classes:

ExpressionVirtualColumn, FallbackVirtualColumn, ListFilteredVirtualColumn, NestedFieldVirtualColumn, SettableLongVirtualColumn

public interface VirtualColumn
extends Cacheable

Virtual columns are "views" created over a ColumnSelectorFactory or ColumnSelector. They can potentially draw from multiple underlying columns, although they always present themselves as if they were a single column. A virtual column object will be shared amongst threads and must be thread safe. The selectors returned from the various makeXXXSelector methods need not be thread safe.

Method Summary

Modifier and Type	Method	Description
default boolean	canVectorize(ColumnInspector inspector)
ColumnCapabilities	capabilities(String columnName)	Deprecated.
default ColumnCapabilities	capabilities(ColumnInspector inspector, String columnName)	Return the ColumnCapabilities which best describe the optimal selector to read from this virtual column.
default ColumnIndexSupplier	getIndexSupplier(String columnName, ColumnSelector columnSelector)	Get the ColumnIndexSupplier for the specified virtual column, with the assistance of a ColumnSelector to allow reading things from segments.
String	getOutputName()	Output name of this column.
ColumnValueSelector<?>	makeColumnValueSelector(String columnName, ColumnSelectorFactory factory)	Build a ColumnValueSelector corresponding to this virtual column.
default ColumnValueSelector<?>	makeColumnValueSelector(String columnName, ColumnSelector columnSelector, ReadableOffset offset)	Returns similar ColumnValueSelector object as returned by makeColumnValueSelector(String, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
DimensionSelector	makeDimensionSelector(DimensionSpec dimensionSpec, ColumnSelectorFactory factory)	Build a selector corresponding to this virtual column.
default DimensionSelector	makeDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableOffset offset)	Returns similar DimensionSelector object as returned by makeDimensionSelector(DimensionSpec, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
default MultiValueDimensionVectorSelector	makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableVectorOffset offset)	Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
default MultiValueDimensionVectorSelector	makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)	Build a MultiValueDimensionVectorSelector corresponding to this virtual column.
default SingleValueDimensionVectorSelector	makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec, ColumnSelector columnSelector, ReadableVectorOffset offset)	Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
default SingleValueDimensionVectorSelector	makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec, VectorColumnSelectorFactory factory)	Build a SingleValueDimensionVectorSelector corresponding to this virtual column.
default VectorObjectSelector	makeVectorObjectSelector(String columnName, ColumnSelector columnSelector, ReadableVectorOffset offset)	Returns similar VectorObjectSelector object as returned by makeVectorObjectSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
default VectorObjectSelector	makeVectorObjectSelector(String columnName, VectorColumnSelectorFactory factory)	Build a VectorObjectSelector corresponding to this virtual column.
default VectorValueSelector	makeVectorValueSelector(String columnName, ColumnSelector columnSelector, ReadableVectorOffset offset)	Returns similar VectorValueSelector object as returned by makeVectorValueSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation.
default VectorValueSelector	makeVectorValueSelector(String columnName, VectorColumnSelectorFactory factory)	Build a VectorValueSelector corresponding to this virtual column.
List<String>	requiredColumns()	Returns a list of columns that this virtual column will access.
boolean	usesDotNotation()	Indicates that this virtual column can be referenced with dot notation.

Methods inherited from interface org.apache.druid.java.util.common.Cacheable

getCacheKey

Method Detail

getOutputName

String getOutputName()

Output name of this column.

Returns:

name

makeDimensionSelector

DimensionSelector makeDimensionSelector(DimensionSpec dimensionSpec,
                                        ColumnSelectorFactory factory)

Build a selector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the dimensionSpec.

makeDimensionSelector

@Nullable
default DimensionSelector makeDimensionSelector(DimensionSpec dimensionSpec,
                                                ColumnSelector columnSelector,
                                                ReadableOffset offset)

Returns similar DimensionSelector object as returned by makeDimensionSelector(DimensionSpec, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible. Typically this can not be called in query paths on top of IncrementalIndex which doesn't have columns as in persisted segments.

makeColumnValueSelector

ColumnValueSelector<?> makeColumnValueSelector(String columnName,
                                               ColumnSelectorFactory factory)

Build a ColumnValueSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.

makeColumnValueSelector

@Nullable
default ColumnValueSelector<?> makeColumnValueSelector(String columnName,
                                                       ColumnSelector columnSelector,
                                                       ReadableOffset offset)

Returns similar ColumnValueSelector object as returned by makeColumnValueSelector(String, ColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible. Typically this can not be called in query paths on top of IncrementalIndex which doesn't have columns as in persisted segments.

canVectorize

default boolean canVectorize(ColumnInspector inspector)

makeSingleValueVectorDimensionSelector

default SingleValueDimensionVectorSelector makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                  VectorColumnSelectorFactory factory)

Build a SingleValueDimensionVectorSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the DimensionSpec.

makeSingleValueVectorDimensionSelector

@Nullable
default SingleValueDimensionVectorSelector makeSingleValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                  ColumnSelector columnSelector,
                                                                                  ReadableVectorOffset offset)

Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.

makeMultiValueVectorDimensionSelector

default MultiValueDimensionVectorSelector makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                VectorColumnSelectorFactory factory)

Build a MultiValueDimensionVectorSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with (through DimensionSpec.getDimension(), which is useful if this column uses dot notation. The virtual column is expected to apply any necessary decoration from the DimensionSpec.

makeMultiValueVectorDimensionSelector

@Nullable
default MultiValueDimensionVectorSelector makeMultiValueVectorDimensionSelector(DimensionSpec dimensionSpec,
                                                                                ColumnSelector columnSelector,
                                                                                ReadableVectorOffset offset)

Returns similar SingleValueDimensionVectorSelector object as returned by makeSingleValueVectorDimensionSelector(DimensionSpec, ColumnSelector, ReadableVectorOffset) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.

makeVectorValueSelector

default VectorValueSelector makeVectorValueSelector(String columnName,
                                                    VectorColumnSelectorFactory factory)

Build a VectorValueSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.

makeVectorValueSelector

@Nullable
default VectorValueSelector makeVectorValueSelector(String columnName,
                                                    ColumnSelector columnSelector,
                                                    ReadableVectorOffset offset)

Returns similar VectorValueSelector object as returned by makeVectorValueSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.

makeVectorObjectSelector

default VectorObjectSelector makeVectorObjectSelector(String columnName,
                                                      VectorColumnSelectorFactory factory)

Build a VectorObjectSelector corresponding to this virtual column. Also provides the name that the virtual column was referenced with, which is useful if this column uses dot notation.

makeVectorObjectSelector

@Nullable
default VectorObjectSelector makeVectorObjectSelector(String columnName,
                                                      ColumnSelector columnSelector,
                                                      ReadableVectorOffset offset)

Returns similar VectorObjectSelector object as returned by makeVectorObjectSelector(String, VectorColumnSelectorFactory) except this method has full access to the underlying column and can potentially provide a more efficient implementation. Users of this interface must ensure to first call this method whenever possible.

capabilities

@Deprecated
ColumnCapabilities capabilities(String columnName)

Deprecated.

This method is deprecated in favor of capabilities(ColumnInspector, String), which should be used whenever possible and can support virtual column implementations that need to inspect other columns as inputs. This is a fallback implementation to return the capabilities of this virtual column, which includes a type that corresponds to the best performing base selector supertype (e. g. BaseLongColumnValueSelector) of the object, returned from makeColumnValueSelector(String, ColumnSelectorFactory). May vary based on columnName if this column uses dot notation.

Parameters:

columnName - the name this virtual column was referenced with

Returns:

capabilities, must not be null

capabilities

@Nullable
default ColumnCapabilities capabilities(ColumnInspector inspector,
                                        String columnName)

Return the ColumnCapabilities which best describe the optimal selector to read from this virtual column.

The ColumnInspector (most likely corresponding to an underlying ColumnSelectorFactory of a query) allows the virtual column to consider this information if necessary to compute its output type details.

Examples of this include the ExpressionVirtualColumn, which takes input from other columns and uses the ColumnInspector to infer the output type of expressions based on the types of the inputs.

Parameters:

inspector - column inspector to provide additional information of other available columns

columnName - the name this virtual column was referenced with

Returns:

capabilities, must not be null

requiredColumns

List<String> requiredColumns()

Returns a list of columns that this virtual column will access. This may include the names of other virtual columns. May be empty if a virtual column doesn't access any underlying columns. Does not pass columnName because there is an assumption that the list of columns needed by a dot-notation supporting virtual column will not vary based on the columnName.

Returns:

column names

usesDotNotation

boolean usesDotNotation()

Indicates that this virtual column can be referenced with dot notation. For example, a virtual column named "foo" could be referred to as "foo.bar" with the Cursor it is registered with. In that case, init will be called with columnName "foo.bar" rather than "foo".

Returns:

whether to use dot notation

getIndexSupplier

@Nullable
default ColumnIndexSupplier getIndexSupplier(String columnName,
                                             ColumnSelector columnSelector)

Get the ColumnIndexSupplier for the specified virtual column, with the assistance of a ColumnSelector to allow reading things from segments. If the virtual column has no indexes, this method will return null, or may also return a non-null supplier whose methods may return null values - having a supplier is no guarantee that the column has indexes.