com.apple.foundationdb.record.query.plan.temp

Interface PlannerProperty<T>

Type Parameters:

T - the result type of the property

All Known Implementing Classes:

CreatesDuplicatesProperty, FieldWithComparisonCountProperty, PredicateHeightProperty, RecordTypesProperty, RelationalExpressionDepthProperty, TypeFilterCountProperty, UnmatchedFieldsProperty

@API(value=EXPERIMENTAL)
public interface PlannerProperty<T>

An interface for certain Cascades-style properties, which are measurable features of an expression other than the structure of the expression tree. In particular, a PlannerProperty is a property that depends on (much of) the contents of the subtree rooted at the expression on which it is evaluated, rather than just a finite depth set of paths as a ExpressionMatcher would. For example, the sort order and set of record types produced by a RelationalPlannerExpression could be a PlannerProperty.

To avoid littering PlannerExpression classes with methods for various properties, properties are implemented using a variant of the hierarchical visitor pattern the tree of PlannerExpressions and ExpressionRefs. A property can be evaluated against an expression tree by having the visitor traverse the tree. Note that the "visitLeave()" methods evaluateAtExpression(com.apple.foundationdb.record.query.plan.temp.PlannerExpression, java.util.List<T>) and evaluateAtRef(com.apple.foundationdb.record.query.plan.temp.ExpressionRef<? extends com.apple.foundationdb.record.query.plan.temp.PlannerExpression>, java.util.List<T>) are handed the results of the visitor evaluated at their children and members respectively. Since most properties are easy to describe as a recursion with depth one, this makes properties easier to read and write.

Method Summary

Modifier and Type	Method and Description
T	evaluateAtExpression(PlannerExpression expression, List<T> childResults) Evaluate the property at the given expression, using the results of evaluating the property at its children.
T	evaluateAtRef(ExpressionRef<? extends PlannerExpression> ref, List<T> memberResults) Evaluate the property at the given reference, using the results of evaluating the property at its members.
boolean	shouldVisit(ExpressionRef<? extends PlannerExpression> ref) Return whether the property should visit the subtree rooted at the given expression.
boolean	shouldVisit(PlannerExpression expression) Return whether the property should visit the subtree rooted at the given expression.

Method Detail

shouldVisit

boolean shouldVisit(@Nonnull
                    PlannerExpression expression)

Return whether the property should visit the subtree rooted at the given expression. Called on nodes in the expression tree in visit pre-order of the depth-first traversal of the tree. That is, as each node is visited for the first time, shouldVisit() is called on that node. If shouldVisit() returns false, then evaluateAtExpression(PlannerExpression, List) will not be called on the given expression.

Parameters:

expression - the planner expression to visit

Returns:

true if the children of expression should be visited and false if they should not be visited

shouldVisit

boolean shouldVisit(@Nonnull
                    ExpressionRef<? extends PlannerExpression> ref)

Return whether the property should visit the subtree rooted at the given expression. Called on nodes in the expression tree in visit pre-order of the depth-first traversal of the tree. That is, as each node is visited for the first time, shouldVisit() is called on that node. If shouldVisit() returns false, then evaluateAtRef(ExpressionRef, List) will not be called on the given expression.

Parameters:

ref - the expression reference to visit

Returns:

true if the members of ref should be visited and false if they should not be visited

evaluateAtExpression

@Nonnull
T evaluateAtExpression(@Nonnull
                                PlannerExpression expression,
                                @Nonnull
                                List<T> childResults)

Evaluate the property at the given expression, using the results of evaluating the property at its children. Called on nodes in the expression tree in visit post-order of the depth-first traversal of the tree. That is, as each node is visited for the last time (after all of its children have been visited, if applicable), evaluateAtExpression() is called on that node.

Parameters:

expression - the cursor to visit

childResults - the results of the property evaluated at the children of expression

Returns:

the value of property at the given expression

evaluateAtRef

@Nonnull
T evaluateAtRef(@Nonnull
                         ExpressionRef<? extends PlannerExpression> ref,
                         @Nonnull
                         List<T> memberResults)

Evaluate the property at the given reference, using the results of evaluating the property at its members. Called on nodes in the expression tree in visit post-order of the depth-first traversal of the tree. That is, as each node is visited for the last time (after all of its children have been visited, if applicable), evaluateAtRef() is called on that node.

Parameters:

ref - the expression reference to visit

memberResults - the results of the property evaluated at the members of ref

Returns:

the value of property at the given reference