org.intermine.sql.precompute.LimitOffsetQuery Maven / Gradle / Ivy
package org.intermine.sql.precompute;
/*
* Copyright (C) 2002-2022 FlyMine
*
* This code may be freely distributed and modified under the
* terms of the GNU Lesser General Public Licence. This should
* be distributed with the code. See the LICENSE file for more
* information or http://www.gnu.org/copyleft/lesser.html.
*
*/
/**
* A class specifically for use with the OptimiserCache, designed to split a SQL string into
* its functional part, and the limit and offset.
*
* @author Matthew Wakeling
*/
public class LimitOffsetQuery
{
private String query;
private int limit;
private int offset;
private static final int START = 0;
private static final int NUMBER = 1;
private static final int GOT_NUMBER = 2;
private static final int T = 3;
private static final int OFFSET_E = 4;
private static final int OFFSET_S = 5;
private static final int OFFSET_F2 = 6;
private static final int OFFSET_F1 = 7;
private static final int OFFSET_O = 8;
private static final int LIMIT_I2 = 9;
private static final int LIMIT_M = 10;
private static final int LIMIT_I1 = 11;
private static final int LIMIT_L = 12;
private static final int FINISHED = 13;
private static final int FINISHED_WELL = 14;
/**
* Creates a new LimitOffsetQuery object from this query string.
*
* @param in the SQL query String
*/
public LimitOffsetQuery(String in) {
// Load of parsing here. Probably best to start from the end of the query, and work back.
int state = START;
int multiplier = 1;
int number = 0;
int pos = in.length() - 1;
limit = Integer.MAX_VALUE;
offset = 0;
while ((state != FINISHED) && (state != FINISHED_WELL)) {
char c = in.charAt(pos);
pos--;
switch (state) {
case START:
if (c == ' ') {
state = START;
} else if ((c >= '0') && (c <= '9')) {
state = NUMBER;
number = c - '0';
multiplier = 10;
} else {
state = FINISHED;
}
break;
case NUMBER:
if (c == ' ') {
state = GOT_NUMBER;
} else if ((c >= '0') && (c <= '9')) {
number += multiplier * (c - '0');
multiplier *= 10;
} else {
state = FINISHED;
}
break;
case GOT_NUMBER:
if ((c == 'T') || (c == 't')) {
state = T;
} else {
state = FINISHED;
}
break;
case T:
if ((c == 'E') || (c == 'e')) {
state = OFFSET_E;
} else if ((c == 'I') || (c == 'i')) {
state = LIMIT_I2;
} else {
state = FINISHED;
}
break;
case OFFSET_E:
if ((c == 'S') || (c == 's')) {
state = OFFSET_S;
} else {
state = FINISHED;
}
break;
case OFFSET_S:
if ((c == 'F') || (c == 'f')) {
state = OFFSET_F2;
} else {
state = FINISHED;
}
break;
case OFFSET_F2:
if ((c == 'F') || (c == 'f')) {
state = OFFSET_F1;
} else {
state = FINISHED;
}
break;
case OFFSET_F1:
if ((c == 'O') || (c == 'o')) {
state = OFFSET_O;
} else {
state = FINISHED;
}
break;
case OFFSET_O:
if (c == ' ') {
state = START;
offset = number;
} else {
state = FINISHED;
}
break;
case LIMIT_I2:
if ((c == 'M') || (c == 'm')) {
state = LIMIT_M;
} else {
state = FINISHED;
}
break;
case LIMIT_M:
if ((c == 'I') || (c == 'i')) {
state = LIMIT_I1;
} else {
state = FINISHED;
}
break;
case LIMIT_I1:
if ((c == 'L') || (c == 'l')) {
state = LIMIT_L;
} else {
state = FINISHED;
}
break;
case LIMIT_L:
if (c == ' ') {
state = FINISHED_WELL;
limit = number;
} else {
state = FINISHED;
}
break;
default:
throw new Error("Unrecognised state " + state);
}
}
if (state == FINISHED) {
limit = Integer.MAX_VALUE;
offset = 0;
query = in;
} else {
query = in.substring(0, pos + 1);
}
}
/**
* Getter for the stripped query.
*
* @return the stripped String
*/
public String getQuery() {
return query;
}
/**
* Getter for limit.
*
* @return limit
*/
public int getLimit() {
return limit;
}
/**
* Getter for offset.
*
* @return offset
*/
public int getOffset() {
return offset;
}
/**
* Reconstruct a SQL string, given this alternative SQL query-part.
*
* @param in the new SQL query minus the LIMIT and OFFSET
* @return in plus the LIMIT and OFFSET
*/
public String reconstruct(String in) {
return in + (limit == Integer.MAX_VALUE ? "" : " LIMIT " + limit)
+ (offset == 0 ? "" : " OFFSET " + offset);
}
}
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