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/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* License: GNU Lesser General Public License (LGPL), version 2.1 or later.
* See the lgpl.txt file in the root directory or .
*/
package com.github.drinkjava2.hibernate;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* LIMIT clause handler compatible with SQL Server 2005 and later.
*
* @author Lukasz Antoniak (lukasz dot antoniak at gmail dot com)
* @author Chris Cranford
* @author Yong Zhu(modify)
*/
public class SQLServer2005LimitHandler extends AbstractLimitHandler {
private static final String SELECT = "select";
private static final String FROM = "from";
private static final String DISTINCT = "distinct";
private static final String ORDER_BY = "order by";
private static final String SELECT_DISTINCT = SELECT + " " + DISTINCT;
private static final String SELECT_DISTINCT_SPACE = SELECT_DISTINCT + " ";
static final String SELECT_SPACE = "select ";
private static final Pattern SELECT_DISTINCT_PATTERN = buildShallowIndexPattern(SELECT_DISTINCT_SPACE, true);
private static final Pattern SELECT_PATTERN = buildShallowIndexPattern(SELECT + "(.*)", true);
private static final Pattern FROM_PATTERN = buildShallowIndexPattern(FROM, true);
private static final Pattern ORDER_BY_PATTERN = buildShallowIndexPattern(ORDER_BY, true);
private static final Pattern COMMA_PATTERN = buildShallowIndexPattern(",", false);
private static final Pattern ALIAS_PATTERN = Pattern
.compile("(?![^\\[]*(\\]))\\S+\\s*(\\s(?i)as\\s)\\s*(\\S+)*\\s*$|(?![^\\[]*(\\]))\\s+(\\S+)$");
// Flag indicating whether TOP(?) expression has been added to the original
// query.
protected boolean topAdded;
/**
* Constructs a SQLServer2005LimitHandler
*/
public SQLServer2005LimitHandler() {
// NOP
}
@Override
public boolean supportsLimit() {
return true;
}
@Override
public boolean useMaxForLimit() {
return true;
}
@Override
public boolean supportsLimitOffset() {
return true;
}
@Override
public boolean supportsVariableLimit() {
return true;
}
@Override
public int convertToFirstRowValue(int zeroBasedFirstResult) {
// Our dialect paginated results aren't zero based. The first row should
// get the number 1 and so on
return zeroBasedFirstResult + 1;
}
/**
* Add a LIMIT clause to the given SQL SELECT (HHH-2655: ROW_NUMBER for
* Paging)
*
* The LIMIT SQL will look like:
*
*
* WITH query AS (
* SELECT inner_query.*
* , ROW_NUMBER() OVER (ORDER BY CURRENT_TIMESTAMP) as __hibernate_row_nr__
* FROM ( original_query_with_top_if_order_by_present_and_all_aliased_columns ) inner_query
* )
* SELECT alias_list FROM query WHERE __hibernate_row_nr__ >= offset AND __hibernate_row_nr__ < offset + last
*
*
* When offset equals {@literal 0}, only TOP(?) expression is
* added to the original query.
*
* @return A new SQL statement with the LIMIT clause applied.
*/
@Override
public String processSql(String sql, RowSelection selection) {
final StringBuilder sb = new StringBuilder(sql);
if (sb.charAt(sb.length() - 1) == ';') {
sb.setLength(sb.length() - 1);
}
if (LimitHelper.hasFirstRow(selection)) {
final String selectClause = fillAliasInSelectClause(sb);
final int orderByIndex = shallowIndexOfPattern(sb, ORDER_BY_PATTERN, 0);
if (orderByIndex > 0) {
// ORDER BY requires using TOP.
addTopExpression(sb);
}
encloseWithOuterQuery(sb);
// Wrap the query within a with statement:
sb.insert(0, "WITH query AS (").append(") SELECT ").append(selectClause).append(" FROM query ");
sb.append("WHERE __hibernate_row_nr__ >= ? AND __hibernate_row_nr__ < ?");
} else {
addTopExpression(sb);
}
return sb.toString();
}
@Override
public int bindLimitParametersAtStartOfQuery(RowSelection selection, PreparedStatement statement, int index)
throws SQLException {
if (topAdded) {
// Binding TOP(?)
statement.setInt(index, getMaxOrLimit(selection) - 1);
return 1;
}
return 0;
}
@Override
public int bindLimitParametersAtEndOfQuery(RowSelection selection, PreparedStatement statement, int index)
throws SQLException {
return LimitHelper.hasFirstRow(selection) ? super.bindLimitParametersAtEndOfQuery(selection, statement, index)
: 0;
}
/**
* Adds missing aliases in provided SELECT clause and returns coma-separated
* list of them. If query takes advantage of expressions like {@literal *}
* or {@literal {table}.*} inside SELECT clause, method returns
* {@literal *}.
*
* @param sb
* SQL query.
*
* @return List of aliases separated with comas or {@literal *}.
*/
protected String fillAliasInSelectClause(StringBuilder sb) {
final String separator = System.lineSeparator();
final List aliases = new LinkedList();// NOSONAR
final int startPos = getSelectColumnsStartPosition(sb);
int endPos = shallowIndexOfPattern(sb, FROM_PATTERN, startPos);
int nextComa = startPos;
int prevComa = startPos;
int unique = 0;
boolean selectsMultipleColumns = false;
while (nextComa != -1) {
prevComa = nextComa;
nextComa = shallowIndexOfPattern(sb, COMMA_PATTERN, nextComa);
if (nextComa > endPos) {
break;
}
if (nextComa != -1) {
final String expression = sb.substring(prevComa, nextComa);
if (selectsMultipleColumns(expression)) {
selectsMultipleColumns = true;
} else {
String alias = getAlias(expression);
if (alias == null) {// NOSONAR
// Inserting alias. It is unlikely that we would have to
// add alias, but just in case.
alias = StringHelper.generateAlias("alias", unique);
sb.insert(nextComa, " as " + alias);
final int aliasExprLength = (" as " + alias).length();
++unique;
nextComa += aliasExprLength;
endPos += aliasExprLength;
}
aliases.add(alias);
}
++nextComa;
}
}
// Processing last column.
// Refreshing end position, because we might have inserted new alias.
endPos = shallowIndexOfPattern(sb, FROM_PATTERN, startPos);
final String expression = sb.substring(prevComa, endPos);
if (selectsMultipleColumns(expression)) {
selectsMultipleColumns = true;
} else {
String alias = getAlias(expression);
if (alias == null) {
// Inserting alias. It is unlikely that we would have to add
// alias, but just in case.
alias = StringHelper.generateAlias("alias", unique);
final boolean endWithSeparator = sb.substring(endPos - separator.length()).startsWith(separator);
sb.insert(endPos - (endWithSeparator ? 2 : 1), " as " + alias);
}
aliases.add(alias);
}
// In case of '*' or '{table}.*' expressions adding an alias breaks SQL
// syntax, returning '*'.
return selectsMultipleColumns ? "*" : StringHelper.join(", ", aliases.iterator());
}
/**
* Get the start position for where the column list begins.
*
* @param sb
* the string builder sql.
* @return the start position where the column list begins.
*/
private int getSelectColumnsStartPosition(StringBuilder sb) {
final int startPos = getSelectStartPosition(sb);
// adjustment for 'select distinct ' and 'select '.
final String sql = sb.toString().substring(startPos).toLowerCase();
if (sql.startsWith(SELECT_DISTINCT_SPACE)) {
return startPos + SELECT_DISTINCT_SPACE.length();
} else if (sql.startsWith(SELECT_SPACE)) {
return startPos + SELECT_SPACE.length();
}
return startPos;
}
/**
* Get the select start position.
*
* @param sb
* the string builder sql.
* @return the position where {@code select} is found.
*/
private int getSelectStartPosition(StringBuilder sb) {
return shallowIndexOfPattern(sb, SELECT_PATTERN, 0);
}
/**
* @param expression
* Select expression.
*
* @return {@code true} when expression selects multiple columns,
* {@code false} otherwise.
*/
private boolean selectsMultipleColumns(String expression) {
final String lastExpr = expression.trim().replaceFirst("(?i)(.)*\\s", "").trim();
return "*".equals(lastExpr) || lastExpr.endsWith(".*");
}
/**
* Returns alias of provided single column selection or {@code null} if not
* found. Alias should be preceded with {@code AS} keyword.
*
* @param expression
* Single column select expression.
*
* @return Column alias.
*/
private String getAlias(String expression) {
// remove any function arguments, if any exist.
// 'cast(tab1.col1 as varchar(255)) as col1' -> 'cast as col1'
// 'cast(tab1.col1 as varchar(255)) col1 -> 'cast col1'
// 'cast(tab1.col1 as varchar(255))' -> 'cast'
expression = expression.replaceFirst("(\\((.)*\\))", "").trim();// NOSONAR
// This will match any text provided with:
// columnName [[as] alias]
final Matcher matcher = ALIAS_PATTERN.matcher(expression);
String alias = null;
if (matcher.find() && matcher.groupCount() > 1) {
// default to the alias after 'as' if detected
alias = matcher.group(3);
if (alias == null) {
// use the clause which has on proceeding 'as' fragment.
alias = matcher.group(0);
}
}
return alias != null ? alias.trim() : null;
}
/**
* Encloses original SQL statement with outer query that provides
* {@literal __hibernate_row_nr__} column.
*
* @param sql
* SQL query.
*/
protected void encloseWithOuterQuery(StringBuilder sql) {
sql.insert(0,
"SELECT inner_query.*, ROW_NUMBER() OVER (ORDER BY CURRENT_TIMESTAMP) as __hibernate_row_nr__ FROM ( ");
sql.append(" ) inner_query ");
}
/**
* Adds {@code TOP} expression. Parameter value is bind in
* {@link #bindLimitParametersAtStartOfQuery(RowSelection, PreparedStatement, int)}
* method.
*
* @param sql
* SQL query.
*/
protected void addTopExpression(StringBuilder sql) {
// We should use either of these which come first (SELECT or SELECT
// DISTINCT).
final int selectPos = shallowIndexOfPattern(sql, SELECT_PATTERN, 0);
final int selectDistinctPos = shallowIndexOfPattern(sql, SELECT_DISTINCT_PATTERN, 0);
if (selectPos == selectDistinctPos) {
// Place TOP after SELECT DISTINCT
sql.insert(selectDistinctPos + SELECT_DISTINCT.length(), " $Top_Tag(?) ");
} else {
// Place TOP after SELECT
sql.insert(selectPos + SELECT.length(), " $Top_Tag(?) ");
}
topAdded = true;
}
/**
* Returns index of the first case-insensitive match of search pattern that
* is not enclosed in parenthesis.
*
* @param sb
* String to search.
* @param pattern
* Compiled search pattern.
* @param fromIndex
* The index from which to start the search.
*
* @return Position of the first match, or {@literal -1} if not found.
*/
private static int shallowIndexOfPattern(final StringBuilder sb, final Pattern pattern, int fromIndex) {
int index = -1;
final String matchString = sb.toString();
// quick exit, save performance and avoid exceptions
if (matchString.length() < fromIndex || fromIndex < 0) {
return -1;
}
List ignoreRangeList = generateIgnoreRanges(matchString);
Matcher matcher = pattern.matcher(matchString);
matcher.region(fromIndex, matchString.length());
if (ignoreRangeList.isEmpty()) {
// old behavior where the first match is used if no ignorable ranges
// were deduced from the matchString.
if (matcher.find() && matcher.groupCount() > 0) {
index = matcher.start();
}
} else {
// rather than taking the first match, we now iterate all matches
// until we determine a match that isn't considered "ignorable'.
while (matcher.find() && matcher.groupCount() > 0) {
final int position = matcher.start();
if (!isPositionIgnorable(ignoreRangeList, position)) {
index = position;
break;
}
}
}
return index;
}
/**
* Builds a pattern that can be used to find matches of case-insensitive
* matches based on the search pattern that is not enclosed in parenthesis.
*
* @param pattern
* String search pattern.
* @param wordBoundary
* whether to apply a word boundary restriction.
* @return Compiled {@link Pattern}.
*/
private static Pattern buildShallowIndexPattern(String pattern, boolean wordBoundary) {
return Pattern.compile(
"(" + (wordBoundary ? "\\b" : "") + pattern + (wordBoundary ? "\\b" : "") + ")(?![^\\(|\\[]*(\\)|\\]))",
Pattern.CASE_INSENSITIVE);
}
/**
* Geneartes a list of {@code IgnoreRange} objects that represent nested
* sections of the provided SQL buffer that should be ignored when
* performing regular expression matches.
*
* @param sql
* The SQL buffer.
* @return list of {@code IgnoreRange} objects, never {@code null}.
*/
private static List generateIgnoreRanges(String sql) {
List ignoreRangeList = new ArrayList();// NOSONAR
int depth = 0;
int start = -1;
for (int i = 0; i < sql.length(); ++i) {
final char ch = sql.charAt(i);
if (ch == '(') {
depth++;
if (depth == 1) {
start = i;
}
} else if (ch == ')') {
if (depth > 0) {
if (depth == 1) {// NOSONAR
ignoreRangeList.add(new IgnoreRange(start, i));
start = -1;
}
depth--;
} else {
throw new IllegalStateException("Found an unmatched ')' at position " + i + ": " + sql);
}
}
}
if (depth != 0) {
throw new IllegalStateException("Unmatched parenthesis in rendered SQL (" + depth + " depth): " + sql);
}
return ignoreRangeList;
}
/**
* Returns whether the specified {@code position} is within the ranges of
* the {@code ignoreRangeList}.
*
* @param ignoreRangeList
* list of {@code IgnoreRange} objects deduced from the SQL
* buffer.
* @param position
* the position to determine whether is ignorable.
* @return {@code true} if the position is to ignored/skipped, {@code false}
* otherwise.
*/
private static boolean isPositionIgnorable(List ignoreRangeList, int position) {
for (IgnoreRange ignoreRange : ignoreRangeList) {
if (ignoreRange.isWithinRange(position)) {
return true;
}
}
return false;
}
static class IgnoreRange {
private int start;
private int end;
IgnoreRange(int start, int end) {
this.start = start;
this.end = end;
}
boolean isWithinRange(int position) {
return position >= start && position <= end;
}
}
}