Package com.almworks.jira.structure.api.attribute.loader.reduce

Interface ReductionStrategy<T>

Type Parameters:

T - type of reduced data

All Known Implementing Classes:

ReductionStrategy.AbstractReductionStrategy, ReductionStrategy.ChildrenReductionStrategy, ReductionStrategy.LeavesReductionStrategy, ReductionStrategy.StrictReductionStrategy, ReductionStrategy.SubtreeReductionStrategy

public interface ReductionStrategy<T>

Describes a part of subtree to be used for calculating aggregate values. Subtree type can be:

• subtree: full subtree (default),
• strict: subtree without root node,
• children: direct children only,
• leaves: leaves only.

The way it works is that apply(java.util.function.Supplier<com.almworks.jira.structure.api.attribute.AttributeValue<T>>, java.util.List<com.almworks.jira.structure.api.attribute.AttributeValue<T>>, com.almworks.jira.structure.api.attribute.loader.reduce.ValueReducer<T>) is called from AttributeLoader.Aggregate.loadValue, and it passes the values corresponding to the specific part of the subtree to a ValueReducer.

Implementations provide the way to effectively calculate reduction on given subtree. They may use (but may ignore) AttributeValue.value of the current row. They may also use AttributeValue.loaderData for intermediate calculations. Every implementation defines its own contract for attribute value and loader data. If an implementation uses loader data, it should check for errors. It doesn't need to check for errors in attribute values because the check should be performed by the caller code.

This class is intended to be an inner utility of ReducingAggregateLoader and similar classes. First an ReductionStrategy instance is retrieved using forAttributeSpec(com.almworks.jira.structure.api.attribute.AttributeSpec<?>), which looks at SharedAttributeSpecs.Param.TYPE parameter in the attribute specification. Default recognized subtree types are described in forStrategyType(java.lang.String). Typical usage is to implement aggregation modifiers in formulas.

See Also:

• ValueReducer
• ReducingAggregateLoader

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static class	ReductionStrategy.AbstractReductionStrategy<T>
static class	ReductionStrategy.ChildrenReductionStrategy<T>	Main value: the aggregation based only on children.
static class	ReductionStrategy.LeavesReductionStrategy<T>	Main value: the aggregation based only on leaves.
static class	ReductionStrategy.StrictReductionStrategy<T>	Main value: the aggregation based on the whole subtree without self row.
static class	ReductionStrategy.SubtreeReductionStrategy<T>	Main value: the aggregation based only on all children.

Method Summary

Modifier and Type	Method	Description
AttributeValue<T>	apply(Supplier<AttributeValue<T>> selfSupplier, List<AttributeValue<T>> children, ValueReducer<T> reducer)	Reduce value of the current node and children values to the single value using the specified ValueReducer.
static <T> ReductionStrategy<T>	forAttributeSpec(AttributeSpec<?> attributeSpec)	Look for strategy type from the spec and try to return default strategy for known types.
static <T> ReductionStrategy<T>	forStrategyType(String strategyType)	Try to return default strategy for known types.
static String	getStrategyType(AttributeSpec<?> attributeSpec)	Look for known strategy type from the spec and return default (SUBTREE) value if not found.

Method Details

apply

@NotNull
AttributeValue<T> apply(@NotNull
 Supplier<AttributeValue<T>> selfSupplier,
 @NotNull
 List<AttributeValue<T>> children,
 @NotNull
 ValueReducer<T> reducer)

Reduce value of the current node and children values to the single value using the specified ValueReducer. This method is designed to be used from AttributeLoader.Aggregate. Reduction can be performed over any subtree and it's assumed that every ReductionStrategy describes in this method a reduction for a single known subtree type.

Parameters:

selfSupplier - supplier for value of current row. Supplier can be or be not called from this method depending on type of subtree this strategy describes. It's assumed that calling supplier can be heavy operation so it shouldn't be called more than once for each row from this method.

children - values of direct children rows supplied by AttributeLoader.Aggregate.loadValue

reducer - instance that is responsible for reducing but can ignore actual form of handled subtree

Returns:

reduced subtree value

getStrategyType

@NotNull
static String getStrategyType(@NotNull
 AttributeSpec<?> attributeSpec)

Look for known strategy type from the spec and return default (SUBTREE) value if not found.

Parameters:

attributeSpec - spec to search for strategy type

Returns:

strategy type

forAttributeSpec

@NotNull
static <T> ReductionStrategy<T> forAttributeSpec(@NotNull
 AttributeSpec<?> attributeSpec)

Look for strategy type from the spec and try to return default strategy for known types.

Parameters:

attributeSpec - spec to search for strategy type

Returns:

reduction strategy

Throws:

IllegalArgumentException - iff strategy type is unknown

forStrategyType

@NotNull
static <T> ReductionStrategy<T> forStrategyType(@NotNull
 String strategyType)

Try to return default strategy for known types.

Parameters:

strategyType - strategy type

Returns:

reduction strategy

Throws:

IllegalArgumentException - iff strategy type is unknown