Package org.apache.druid.segment.virtual

Class ExpressionSelectors

java.lang.Object

org.apache.druid.segment.virtual.ExpressionSelectors

public class ExpressionSelectors
extends Object

Method Summary

Modifier and Type	Method	Description
static boolean	canMapOverDictionary(Expr.BindingAnalysis bindingAnalysis, ColumnCapabilities columnCapabilities)	Returns whether an expression can be applied to unique values of a particular column (like those in a dictionary) rather than being applied to each row individually.
static ColumnValueSelector<?>	castColumnValueSelector(RowIdSupplier rowIdSupplier, ColumnValueSelector<?> delegate, ColumnType delegateType, ColumnType castToType)	Wrap the output of BaseObjectColumnValueSelector.getObject() in ExprEval.ofType(ExpressionType, Object) using the supplied delegate type and cast using ExprEval.castTo(org.apache.druid.math.expr.ExpressionType) to convert to the target type.
static Object	coerceEvalToObjectOrList(ExprEval eval)	Coerces ExprEval value back to a ColumnType.STRING selector friendly value, converting into: - the expression value if the value is not an array - the single array element if the value is an array with 1 element - a list with all of the array elements if the value is an array with more than 1 element This method is used by makeStringColumnValueSelector(ColumnSelectorFactory, Expr), which is used exclusively for making ColumnValueSelector when an ExpressionVirtualColumn has STRING output type, and by ExpressionTransform which should be reconsidered if we ever want to add support for ingestion transforms producing ValueType.ARRAY typed outputs.
static Expr.ObjectBinding	createBindings(ColumnSelectorFactory columnSelectorFactory, ExpressionPlan plan)	Create Expr.ObjectBinding given a ColumnSelectorFactory and ExpressionPlan which provides the set of identifiers which need a binding (list of required columns), and context of whether or not they are used as array or scalar inputs
static ColumnValueSelector	makeColumnValueSelector(ColumnSelectorFactory columnSelectorFactory, Expr expression)	Makes a ColumnValueSelector whose getObject method returns an Object that is the value computed by an ExprEval.
static DimensionSelector	makeDimensionSelector(ColumnSelectorFactory columnSelectorFactory, Expr expression, ExtractionFn extractionFn)	Makes a single or multi-value DimensionSelector wrapper around a ColumnValueSelector created by makeExprEvalSelector(ColumnSelectorFactory, Expr) as appropriate
static ColumnValueSelector<ExprEval>	makeExprEvalSelector(ColumnSelectorFactory columnSelectorFactory, Expr expression)	Makes a ColumnValueSelector whose getObject method returns an ExprEval.
static <T> com.google.common.base.Supplier<T>	makeNullableNumericSupplier(ColumnValueSelector selector, com.google.common.base.Supplier<T> supplier)	Wraps a ColumnValueSelector and uses it to supply numeric values in a null-aware way.
static ColumnValueSelector	makeStringColumnValueSelector(ColumnSelectorFactory columnSelectorFactory, Expr expression)

Methods inherited from class java.lang.Object

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

Method Details

makeColumnValueSelector

public static ColumnValueSelector makeColumnValueSelector(ColumnSelectorFactory columnSelectorFactory,
 Expr expression)

Makes a ColumnValueSelector whose getObject method returns an Object that is the value computed by an ExprEval.

See Also:

• makeExprEvalSelector(ColumnSelectorFactory, Expr)

makeStringColumnValueSelector

public static ColumnValueSelector makeStringColumnValueSelector(ColumnSelectorFactory columnSelectorFactory,
 Expr expression)

castColumnValueSelector

public static ColumnValueSelector<?> castColumnValueSelector(RowIdSupplier rowIdSupplier,
 ColumnValueSelector<?> delegate,
 @Nullable
 ColumnType delegateType,
 ColumnType castToType)

Wrap the output of BaseObjectColumnValueSelector.getObject() in ExprEval.ofType(ExpressionType, Object) using the supplied delegate type and cast using ExprEval.castTo(org.apache.druid.math.expr.ExpressionType) to convert to the target type. If the delegate selector type is null, ExprEval.ofType(org.apache.druid.math.expr.ExpressionType, java.lang.Object) falls back to using ExprEval.bestEffortOf(java.lang.Object), however the target type must be not null, or else this method will fail when attempting to convert to an expression type.

makeExprEvalSelector

public static ColumnValueSelector<ExprEval> makeExprEvalSelector(ColumnSelectorFactory columnSelectorFactory,
 Expr expression)

Makes a ColumnValueSelector whose getObject method returns an ExprEval.

See Also:

• makeColumnValueSelector(ColumnSelectorFactory, Expr)

makeDimensionSelector

public static DimensionSelector makeDimensionSelector(ColumnSelectorFactory columnSelectorFactory,
 Expr expression,
 @Nullable
 ExtractionFn extractionFn)

Makes a single or multi-value DimensionSelector wrapper around a ColumnValueSelector created by makeExprEvalSelector(ColumnSelectorFactory, Expr) as appropriate

canMapOverDictionary

public static boolean canMapOverDictionary(Expr.BindingAnalysis bindingAnalysis,
 @Nullable
 ColumnCapabilities columnCapabilities)

Returns whether an expression can be applied to unique values of a particular column (like those in a dictionary) rather than being applied to each row individually. This function should only be called if you have already determined that an expression is over a single column, and that single column has a dictionary.

Parameters:

bindingAnalysis - result of calling Expr.analyzeInputs() on an expression

columnCapabilities - ColumnCapabilities for the input binding

createBindings

public static Expr.ObjectBinding createBindings(ColumnSelectorFactory columnSelectorFactory,
 ExpressionPlan plan)

Create Expr.ObjectBinding given a ColumnSelectorFactory and ExpressionPlan which provides the set of identifiers which need a binding (list of required columns), and context of whether or not they are used as array or scalar inputs

makeNullableNumericSupplier

public static <T>
com.google.common.base.Supplier<T> makeNullableNumericSupplier(ColumnValueSelector selector,
 com.google.common.base.Supplier<T> supplier)

Wraps a ColumnValueSelector and uses it to supply numeric values in a null-aware way.

See Also:

• for why this only works in the numeric case

coerceEvalToObjectOrList

@Nullable
public static Object coerceEvalToObjectOrList(ExprEval eval)

Coerces ExprEval value back to a ColumnType.STRING selector friendly value, converting into: - the expression value if the value is not an array - the single array element if the value is an array with 1 element - a list with all of the array elements if the value is an array with more than 1 element This method is used by makeStringColumnValueSelector(ColumnSelectorFactory, Expr), which is used exclusively for making ColumnValueSelector when an ExpressionVirtualColumn has STRING output type, and by ExpressionTransform which should be reconsidered if we ever want to add support for ingestion transforms producing ValueType.ARRAY typed outputs.