root / trunk / libraries / libGDBMS / src / main / java / com / hardcode / gdbms / engine / strategies / ProjectionDataSource.java @ 10627
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package com.hardcode.gdbms.engine.strategies; |
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import com.hardcode.gdbms.driver.exceptions.ReadDriverException; |
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import com.hardcode.gdbms.engine.data.DataSource; |
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import com.hardcode.gdbms.engine.data.persistence.Memento; |
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import com.hardcode.gdbms.engine.data.persistence.MementoException; |
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import com.hardcode.gdbms.engine.data.persistence.OperationLayerMemento; |
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import com.hardcode.gdbms.engine.instruction.EvaluationException; |
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import com.hardcode.gdbms.engine.instruction.Expression; |
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import com.hardcode.gdbms.engine.values.Value; |
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/**
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* DataSource que a?ade caracter?sticas de proyecci?n sobre campos al
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* DataSource subyacente.
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*
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* @author Fernando Gonz?lez Cort?s
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*/
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public class ProjectionDataSource extends OperationDataSource { |
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private DataSource source; |
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private Expression[] fields; |
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private String[] aliases; |
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/**
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* Creates a new ProjectionDataSource object.
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*
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* @param source DataSource origen de la informaci?n
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* @param fields Con los ?ndices de los campos proyectados
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* @param aliases Nombres asignados en la instrucci?n a los campos
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*/
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public ProjectionDataSource(DataSource source, Expression[] fields, |
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String[] aliases) { |
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this.source = source;
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this.fields = fields;
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this.aliases = aliases;
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} |
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/**
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* Dado el ?ndice de un campo en la tabla proyecci?n, se devuelve el ?ndice
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* real en el DataSource subyacente
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*
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* @param index ?ndice del campo cuyo ?ndice en el DataSource subyacente se
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* quiere obtener
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*
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* @return ?ndice del campo en el DataSource subyacente
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*/
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private Expression getFieldByIndex(int index) { |
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return fields[index];
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public void stop() throws ReadDriverException { |
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source.stop(); |
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public int getFieldCount() throws ReadDriverException { |
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return fields.length;
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public int getFieldIndexByName(String fieldName) throws ReadDriverException { |
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/*
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* Se comprueba si dicho ?ndice est? mapeado o la ProjectionDataSource
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* no lo tiene
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*/
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for (int i = 0; i < fields.length; i++) { |
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if (fieldName.compareTo(fields[i].getFieldName()) == 0) { |
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return i;
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} |
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} |
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return -1; |
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public String getFieldName(int fieldId) throws ReadDriverException { |
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if (aliases[fieldId] != null) { |
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return aliases[fieldId];
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} else {
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String name = fields[fieldId].getFieldName();
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if (name == null) { |
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return "unknown" + fieldId; |
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} else {
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return name;
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} |
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} |
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public Value getFieldValue(long rowIndex, int fieldId) |
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throws ReadDriverException {
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try {
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return getFieldByIndex(fieldId).evaluate(rowIndex);
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} catch (EvaluationException e) {
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throw new ReadDriverException(getName(),e); |
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} |
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public long getRowCount() throws ReadDriverException { |
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return source.getRowCount();
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} |
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/**
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* @see com.hardcode.gdbms.data.DataSource#
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*/
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public void start() throws ReadDriverException { |
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source.start(); |
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} |
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/**
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* @see com.hardcode.gdbms.engine.data.driver.ObjectDriver#getFieldType(int)
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*/
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public int getFieldType(int i) throws ReadDriverException { |
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throw new UnsupportedOperationException( |
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"cannot get the field type of an expression");
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} |
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/**
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* @see com.hardcode.gdbms.engine.data.DataSource#getMemento()
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*/
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public Memento getMemento() throws MementoException { |
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return new OperationLayerMemento(getName(), |
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new Memento[] { source.getMemento() }, getSQL()); |
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} |
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public int getFieldWidth(int i) throws ReadDriverException { |
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throw new UnsupportedOperationException( |
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"cannot get the field width of an expression");
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} |
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} |