com.redhat.lightblue.assoc

Class RewriteQuery

java.lang.Object

com.redhat.lightblue.query.QueryIteratorSkeleton<QueryExpression>

com.redhat.lightblue.query.QueryIterator

com.redhat.lightblue.assoc.RewriteQuery

public class RewriteQuery
extends QueryIterator

Rewrite queries so that any clause referring to a field outside the current entity is removed from the query, and any clause comparing a field in this entity with a field in another entity is bound to a slot. It is not possible to rewrite a query clause referring to a field in another entity. For instance a query of the form x=1 would become meaningless, as 'x' has no value while evaluating this entity. So the clause is removed from the query, and replaced with a placeholder.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	RewriteQuery.FalsePH Placeholder that always evaluates to false
static class	RewriteQuery.RewriteQueryResult
static class	RewriteQuery.TruePH Placeholder that always evaluates to true

Constructor Summary

Constructors

Constructor and Description
RewriteQuery(CompositeMetadata root, CompositeMetadata currentEntity) Construct a class to rewrite queries to retrieve an entity, potentially evaluated at another entity

Method Summary

Modifier and Type	Method and Description
RewriteQuery.RewriteQueryResult	rewriteQuery(QueryExpression q, List<QueryFieldInfo> fieldInfo) Rewrites a query using field information obtained from AnalyzeQuery

Methods inherited from class com.redhat.lightblue.query.QueryIterator

itrAllMatchExpression, itrArrayContainsExpression, itrArrayMatchExpression, itrFieldComparisonExpression, itrNaryFieldRelationalExpression, itrNaryLogicalExpression, itrNaryValueRelationalExpression, itrRegexMatchExpression, itrUnaryLogicalExpression, itrValueComparisonExpression

Methods inherited from class com.redhat.lightblue.query.QueryIteratorSkeleton

iterate, iterate

Methods inherited from class java.lang.Object

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

Constructor Detail

RewriteQuery

public RewriteQuery(CompositeMetadata root,
                    CompositeMetadata currentEntity)

Construct a class to rewrite queries to retrieve an entity, potentially evaluated at another entity

Parameters:

root - The root entity

currentEntity - The query will be rewritten relative to this entity The root entity is the entity that will be retrieved ultimately. That entity may contain associations to other entities, and the association queries need to be rewritten based on the query plan node they are evaluated. The currentEntity gives that node relative to which the queries will be rewritten.

Method Detail

rewriteQuery

public RewriteQuery.RewriteQueryResult rewriteQuery(QueryExpression q,
                                                    List<QueryFieldInfo> fieldInfo)

Rewrites a query using field information obtained from AnalyzeQuery

Returns:

Returns a result object containing the new rewritten query, and the field bindings that will be set to values from already retrieved documents.