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

Classes related to the ViewExpression abstraction.

A view expression is an abstraction that represents a stream of values that can be represented as tuple-encoded keys and binary values in FoundationDB. View expressions are quite general and can represent a large variety of index structures and even queries. However, because they are defined by their close relationship to the FDB tuple layer encoding, they are extremely useful for many query planning operations, such as incremental index selection (for example, see PushElementWithComparisonIntoExistingScanRule).

Semantically, a view expression can be read much like a query in a declarative query language like SQL. For example, it can specify a projection, sort order, and filter predicate. When used to represent the structure of an index, a view expression can be interpreted as a query for which the index acts as a materialized view. ViewExpression describes the specific semantics in further detail.

The two key abstractions that are used for defining view expressions are Sources and Elements. A source represents a stream of entities that can be manipulated to form a view expression, while an element defines the mapping from one entry in a source's stream to a value that can be represented as part of a tuple. For example, the RecordTypeSource represents a stream of records with types from a specified set of record types. A FieldElement produces values from a field of each entry in a stream of records.

During query planning with the Cascades-style planner, Comparisons.Comparisons are matched to elements of a view expression. The state and logic for determining which comparisons can be matched to a (partially matched) view expression is encapsulated in the ViewExpressionComparisons class.

Interface Summary

Interface	Description
Element	A value in the ViewExpression language that can be represented as an element of FoundationDB tuple.

Class Summary

Class	Description
FieldElement	An element that extracts a single, non-repeated field (at an arbitrary nesting depth) from a source.
LiteralElement<T>	A value representing a single, static value of type T.
MessageValue	A utility class for extracting data and meta-data from Protocol Buffer Messages, as used in the Record Layer.
RecordTypeElement	An element representing the record type of each entry generated by the source.
RecordTypeSource	A Source representing the stream of all records of a particular type or types.
RepeatedFieldSource	A Source representing the stream of the zero or more values of a repeated field.
Source	A source represents a stream of entities that can be used to generate Elements, such as records or field values.
SourceEntry	A single entity produced by a source from a record, mapping each (inclusive) dependant source to a concrete value.
ValueElement	An Element representing an entire value, such as a scalar or message, obtained from a source.
VersionElement	An Element representing a serialized versionstamp in a query or index entry.
ViewExpression	An abstraction that represents a stream of values that can be represented as tuple-encoding keys and binary values in FoundationDB.
ViewExpression.Builder	A builder class for constructing an (immutable) view expression.
ViewExpressionComparisons	A data structure that represents a ViewExpression with a ComparisonRange on some of the Elements in its sort order.