uk.ac.ed.epcc.webapp.jdbc.expr

Class ReductionMapper<R>

java.lang.Object

uk.ac.ed.epcc.webapp.AbstractContexed

uk.ac.ed.epcc.webapp.jdbc.expr.ReductionMapper<R>

Type Parameters:

R - type of result

All Implemented Interfaces:

Contexed, ResultMapper<R>

public class ReductionMapper<R>
extends AbstractContexed
implements ResultMapper<R>

A ResultMapper that maps a single SQL reduction to a value of the same type

Field Summary

Fields inherited from class uk.ac.ed.epcc.webapp.AbstractContexed

conn

Constructor Summary

Constructors

Constructor and Description
ReductionMapper(AppContext c, java.lang.Class<R> target, Reduction op, R def, SQLExpression<? extends R> exp)

Method Summary

Modifier and Type	Method and Description
java.lang.String	getModify() provide an override GROUP/ORDER by clause null to use default order from filters
java.util.List<PatternArgument>	getModifyParameters(java.util.List<PatternArgument> list) Add parameters for the GROUP/ORDER clause to a list.
SQLFilter	getRequiredFilter() Get an additional Filter required to make the target string work properly.
java.lang.String	getTarget() get the target clause of the SQL query.
java.util.List<PatternArgument>	getTargetParameters(java.util.List<PatternArgument> list) Add parameters for the target clause to a list.
R	makeDefault() Create a default Object to be returned if no SQL results are generated.
R	makeObject(java.sql.ResultSet rs) Convert a ResultSet into a domain object.
boolean	setQualify(boolean qualify) Request that field names should be qualified with the table name where appropriate.

Methods inherited from class uk.ac.ed.epcc.webapp.AbstractContexed

getContext, getLogger, resetLogger

Methods inherited from class java.lang.Object

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

Constructor Detail

ReductionMapper

public ReductionMapper(AppContext c,
                       java.lang.Class<R> target,
                       Reduction op,
                       R def,
                       SQLExpression<? extends R> exp)

Parameters:

c - AppContext

target - type of result

op - Reduction operation

def - default result

exp - SQLExpression

Method Detail

getModify

public java.lang.String getModify()

Description copied from interface: ResultMapper

provide an override GROUP/ORDER by clause null to use default order from filters

Specified by:

getModify in interface ResultMapper<R>

Returns:

String SQL clause

getTarget

public java.lang.String getTarget()

Description copied from interface: ResultMapper

get the target clause of the SQL query. it makes sense to set it here as it has to match what the ResultMapper is expecting

Specified by:

getTarget in interface ResultMapper<R>

Returns:

String

makeDefault

public R makeDefault()

Description copied from interface: ResultMapper

Create a default Object to be returned if no SQL results are generated. If there is no obvious default result then return null. Where there is an obvious result (like a sum=0 or an empty Map) this is less error prone than trying to trap null at the calling level. Note that FilterFinder can optionally check for null results and generate exceptions this still fails but makes it easier to find the problem.

Specified by:

makeDefault in interface ResultMapper<R>

Returns:

domain object

makeObject

public R makeObject(java.sql.ResultSet rs)
             throws DataException,
                    java.sql.SQLException

Description copied from interface: ResultMapper

Convert a ResultSet into a domain object. The ResultSet should already be positioned at the correct starting Row to start creating the object It is legal for this method to return null to indicate the ResultSet represents an invalid record that should be ignored by the higher levels of the code.

Specified by:

makeObject in interface ResultMapper<R>

Parameters:

rs - ResultSet or null

Returns:

domain object

Throws:

DataException

java.sql.SQLException

setQualify

public boolean setQualify(boolean qualify)

Description copied from interface: ResultMapper

Request that field names should be qualified with the table name where appropriate. This is for use with joined tables. For some result mappers this does not make sense so this method always returns the same value.

Specified by:

setQualify in interface ResultMapper<R>

Returns:

previous value of qualify flag

getRequiredFilter

public SQLFilter getRequiredFilter()

Description copied from interface: ResultMapper

Get an additional Filter required to make the target string work properly. This is usually used to add an additional join.

Specified by:

getRequiredFilter in interface ResultMapper<R>

Returns:

null or SQLFilter

getTargetParameters

public java.util.List<PatternArgument> getTargetParameters(java.util.List<PatternArgument> list)

Description copied from interface: ResultMapper

Add parameters for the target clause to a list.

Specified by:

getTargetParameters in interface ResultMapper<R>

Parameters:

list - to modify

Returns:

modified list of parameter objects

getModifyParameters

public java.util.List<PatternArgument> getModifyParameters(java.util.List<PatternArgument> list)

Description copied from interface: ResultMapper

Add parameters for the GROUP/ORDER clause to a list.

Specified by:

getModifyParameters in interface ResultMapper<R>

Parameters:

list - to modify

Returns:

modified list of parameter objects