com.redhat.lightblue.eval

Class Projector

java.lang.Object

com.redhat.lightblue.eval.Projector

Direct Known Subclasses:

ArrayProjector, FieldProjector, ListProjector

public abstract class Projector
extends Object

This class evaluates a Projection. This is a stateful class. It retains state from the last execution that gets overwritten every time project() is called. This is how a document is projected: all the elements in the document is traversed in a depth first manner. For each field, the projection is evaluated. If the projection evaluated to true, the field is included, and projection continues to the subtree under that field. If the projection evaluates to false, that subtree is excluded. If the projection for that field cannot be decided, the a warning is logged, and field is excluded. Array fields can have nested projections to project their array elements. Recursive inclusion projections don't cross entity boundaries (i.e. references) unless there is an explicit inclusion projection for the referenced entity, or a field under that entity.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Projector(Path ctxPath, FieldTreeNode ctx)

Method Summary

Modifier and Type	Method and Description
static Projector	getInstance(Projection projection, EntityMetadata md) Builds a projector using the given projection and entity metadata
static Projector	getInstance(Projection projection, Path ctxPath, FieldTreeNode ctx) Builds a (potentially nested) projection based on the given projection, and the location in the metadata field tree.
abstract Projector	getNestedProjector() Returns the nested projector for this path *only if* project returns true.
JsonDoc	project(JsonDoc doc, com.fasterxml.jackson.databind.node.JsonNodeFactory factory) Projects a document
abstract Projection.Inclusion	project(Path p, QueryEvaluationContext ctx) Returns true, false, or null if the result cannot be determined.

Methods inherited from class java.lang.Object

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

Constructor Detail

Projector

protected Projector(Path ctxPath,
                    FieldTreeNode ctx)

Method Detail

getNestedProjector

public abstract Projector getNestedProjector()

Returns the nested projector for this path *only if* project returns true. Nested projector is used to project array elements. When a nested projector exists, projection operation should use the nested projector to project array elements. May return null, which means to continue using existing projector (this).

project

public abstract Projection.Inclusion project(Path p,
                                             QueryEvaluationContext ctx)

Returns true, false, or null if the result cannot be determined.

Parameters:

p - The absolute field path

ctx - Query evaluation context

getInstance

public static Projector getInstance(Projection projection,
                                    EntityMetadata md)

Builds a projector using the given projection and entity metadata

getInstance

public static Projector getInstance(Projection projection,
                                    Path ctxPath,
                                    FieldTreeNode ctx)

Builds a (potentially nested) projection based on the given projection, and the location in the metadata field tree.

project

public JsonDoc project(JsonDoc doc,
                       com.fasterxml.jackson.databind.node.JsonNodeFactory factory)

Projects a document