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java.lang.Objectde.fuberlin.wiwiss.d2rq.algebra.MutableRelation
public class MutableRelation
Wraps a relation and allows it to be modified by relational operators. Normally, applying an operator to a relation results in a new object. This is impractical in some places. The MutableRelation solves this problem.
Field Summary |
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Fields inherited from interface de.fuberlin.wiwiss.d2rq.algebra.RelationalOperators |
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DUMMY |
Constructor Summary | |
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MutableRelation(Relation initialState)
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Method Summary | |
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Relation |
empty()
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Relation |
immutableSnapshot()
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Relation |
limit(int limit)
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Relation |
orderBy(List<OrderSpec> orderSpecs)
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Relation |
project(Set<? extends ProjectionSpec> projectionSpecs)
Applies the projection operator to this relation. |
Relation |
renameColumns(ColumnRenamer renamer)
Applies the rename operator to this relation. |
Relation |
select(Expression condition)
Applies the selection operator to this relation. |
Relation |
swapLimits()
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Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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public MutableRelation(Relation initialState)
Method Detail |
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public Relation immutableSnapshot()
public Relation renameColumns(ColumnRenamer renamer)
RelationalOperators
Applies the rename operator to this relation.
Renames of attributes that don't exist in the relation are ignored.
renameColumns
in interface RelationalOperators
renamer
- A map from original to replacement names
public Relation empty()
public Relation select(Expression condition)
RelationalOperators
Applies the selection operator to this relation. The new relation will contain only the tuples for which the expression evaluates to true.
Selection on attributes that don't exist in the relation are considered to be always false and will cause an empty relation.
select
in interface RelationalOperators
condition
- A boolean expression
public Relation orderBy(List<OrderSpec> orderSpecs)
public Relation swapLimits()
public Relation project(Set<? extends ProjectionSpec> projectionSpecs)
RelationalOperators
Applies the projection operator to this relation.
The new relation will contain only the attributes given as the argument.
project
in interface RelationalOperators
projectionSpecs
- A set of ProjectionSpec
instances
public Relation limit(int limit)
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