/*
* Copyright 2004-2023 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.result;
import org.h2.engine.SessionLocal;
import org.h2.expression.Expression;
import org.h2.message.DbException;
import org.h2.value.TypeInfo;
import org.h2.value.Value;
/**
* Lazy execution support for queries.
*
* @author Sergi Vladykin
*/
public abstract class LazyResult extends FetchedResult {
private final SessionLocal session;
private final Expression[] expressions;
private boolean closed;
private long limit;
public LazyResult(SessionLocal session, Expression[] expressions) {
this.session = session;
this.expressions = expressions;
}
public void setLimit(long limit) {
this.limit = limit;
}
@Override
public boolean isLazy() {
return true;
}
@Override
public void reset() {
if (closed) {
throw DbException.getInternalError();
}
rowId = -1L;
afterLast = false;
currentRow = null;
nextRow = null;
}
/**
* Go to the next row and skip it.
*
* @return true if a row exists
*/
public boolean skip() {
if (closed || afterLast) {
return false;
}
currentRow = null;
if (nextRow != null) {
nextRow = null;
return true;
}
if (skipNextRow()) {
return true;
}
afterLast = true;
return false;
}
@Override
public boolean hasNext() {
if (closed || afterLast) {
return false;
}
if (nextRow == null && (limit <= 0 || rowId + 1 < limit)) {
nextRow = fetchNextRow();
}
return nextRow != null;
}
/**
* Fetch next row or null if none available.
*
* @return next row or null
*/
protected abstract Value[] fetchNextRow();
/**
* Skip next row.
*
* @return true if next row was available
*/
protected boolean skipNextRow() {
return fetchNextRow() != null;
}
@Override
public long getRowCount() {
throw DbException.getUnsupportedException("Row count is unknown for lazy result.");
}
@Override
public boolean isClosed() {
return closed;
}
@Override
public void close() {
closed = true;
}
@Override
public String getAlias(int i) {
return expressions[i].getAlias(session, i);
}
@Override
public String getSchemaName(int i) {
return expressions[i].getSchemaName();
}
@Override
public String getTableName(int i) {
return expressions[i].getTableName();
}
@Override
public String getColumnName(int i) {
return expressions[i].getColumnName(session, i);
}
@Override
public TypeInfo getColumnType(int i) {
return expressions[i].getType();
}
@Override
public boolean isIdentity(int i) {
return expressions[i].isIdentity();
}
@Override
public int getNullable(int i) {
return expressions[i].getNullable();
}
@Override
public void setFetchSize(int fetchSize) {
// ignore
}
@Override
public int getFetchSize() {
// We always fetch rows one by one.
return 1;
}
}