com.pervasive.datarush.operators.select

Class LimitRows

java.lang.Object

com.pervasive.datarush.operators.AbstractLogicalOperator

com.pervasive.datarush.operators.CompositeOperator

com.pervasive.datarush.operators.AbstractRecordCompositeOperator

com.pervasive.datarush.operators.select.LimitRows

All Implemented Interfaces:

LogicalOperator, PipelineOperator<RecordPort>, RecordPipelineOperator

public class LimitRows
extends AbstractRecordCompositeOperator

Truncates a flow to a fixed number of records. The output is a "window" on the original input. This operator is most often used on the output of a sort, reducing the original unsorted data to the top N (as measured by the sort criteria).

By default, all records are passed through unless explicitly specified.

Field Summary

Fields inherited from class com.pervasive.datarush.operators.AbstractRecordCompositeOperator

input, output

Constructor Summary

Constructors

Constructor and Description
LimitRows() Performs no truncation of the input flow.
LimitRows(long count) Truncates incoming data to the first N records of the input.
LimitRows(long skip, long count) Truncates incoming data to the first N records following a specified record.

Method Summary

Modifier and Type	Method and Description
protected void	compose(CompositionContext ctx) Compose the body of this operator.
long	getCount() Gets the maximum number of records which will be output.
RecordPort	getInput() Returns the input port
RecordPort	getOutput() Returns the output port
long	getSkip() Gets the number of input records to skip before outputting records.
void	setCount(long count) Sets the maximum number of records which will be output.
void	setSkip(long skip) Sets the number of input records to skip before outputting records.

Methods inherited from class com.pervasive.datarush.operators.AbstractLogicalOperator

disableParallelism, getInputPorts, getOutputPorts, newInput, newInput, newOutput, newRecordInput, newRecordInput, newRecordOutput, notifyError

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.pervasive.datarush.operators.LogicalOperator

disableParallelism, getInputPorts, getOutputPorts

Constructor Detail

LimitRows

public LimitRows()

Performs no truncation of the input flow.

LimitRows

public LimitRows(long count)

Truncates incoming data to the first N records of the input.

Parameters:

count - the number of records to pass through

LimitRows

public LimitRows(long skip,
                 long count)

Truncates incoming data to the first N records following a specified record. Records prior to the start position are discarded; if the input contains insufficient records to reach the starting point, the output will contain no records.

Parameters:

skip - the record at which to start passing through records. Indices are zero-based; that is, the first record is at index 0.

count - the number of records to pass through

Method Detail

getInput

public RecordPort getInput()

Description copied from interface: PipelineOperator

Returns the input port

Specified by:

getInput in interface PipelineOperator<RecordPort>

Overrides:

getInput in class AbstractRecordCompositeOperator

Returns:

the input port

getOutput

public RecordPort getOutput()

Description copied from interface: PipelineOperator

Returns the output port

Specified by:

getOutput in interface PipelineOperator<RecordPort>

Overrides:

getOutput in class AbstractRecordCompositeOperator

Returns:

the output port

getCount

public long getCount()

Gets the maximum number of records which will be output.

Returns:

the limit on the number of output records

setCount

public void setCount(long count)

Sets the maximum number of records which will be output.

Parameters:

count - the limit on the number of output records.

Throws:

InvalidPropertyValueException - if count <= 0

getSkip

public long getSkip()

Gets the number of input records to skip before outputting records.

Returns:

the index of the first record to pass through

setSkip

public void setSkip(long skip)

Sets the number of input records to skip before outputting records.

Parameters:

skip - the index of the first record to pass through

Throws:

InvalidPropertyValueException - if count < 0

compose

protected void compose(CompositionContext ctx)

Description copied from class: CompositeOperator

Compose the body of this operator. Implementations should do the following:

1. Perform any validation of configuration, input types, etc
2. Instantiate and configure sub-operators, adding them to the provided context via the method OperatorComposable.add(O)
3. Create necessary connections via the method OperatorComposable.connect(P, P). This includes connections from the composite's input ports to sub-operators, connections between sub-operators, and connections from sub-operators output ports to the composite's output ports

Specified by:

compose in class CompositeOperator

Parameters:

ctx - the context