aboutsummaryrefslogtreecommitdiff
path: root/engine/lib/database.php
blob: aea310841ad5e28234597de8051c20f76a3c750f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
<?php

	/**
	 * Elgg database
	 * Contains database connection and transfer functionality
	 * 
	 * @package Elgg
	 * @subpackage Core
	 * @license http://www.gnu.org/licenses/old-licenses/gpl-2.0.html GNU Public License version 2
	 * @author Curverider Ltd
	 * @copyright Curverider Ltd 2008
	 * @link http://elgg.org/
	 */

	/**
	 * @class QueryComponent Query component superclass.
	 * Component of a query.
	 * @author Marcus Povey
	 */
	abstract class QueryComponent 
	{
		/**
		 * Associative array of fields and values
		 */ 
		private $fields;

		function __construct()
		{
			$this->fields = array(); 
		}
		
		/**
		 * Class member get overloading
		 *
		 * @param string $name
		 * @return mixed
		 */
		function __get($name) {
			return $this->fields[$name];
		}
		
		/**
		 * Class member set overloading
		 *
		 * @param string $name
		 * @param mixed $value
		 * @return void
		 */
		function __set($name, $value) {
			$this->fields[$name] = $value;
			
			return true;
		}	
	}
	
	/**
	 * @class SelectFieldQueryComponent Class representing a select field.
	 * This class represents a select field component.
	 * @author Marcus Povey
	 */
	class SelectFieldQueryComponent extends QueryComponent 
	{
		/**
		 * Construct a select field component
		 * 
		 * @param string $table The table containing the field.
		 * @param string $field The field or "*"
		 */
		function __construct($table, $field) 
		{
			global $CONFIG;
			
			$this->table = $CONFIG->dbprefix . sanitise_string($table);
			$this->field = sanitise_string($field);
		}
		
		function __toString() 
		{
			return "{$this->table}.{$this->field}";
		}
	}
	
	/**
	 * @class LimitOffsetQueryComponent
	 * Limit and offset clauses of a query.
	 * @author Marcus Povey
	 */
	class LimitOffsetQueryComponent extends QueryComponent
	{
		/**
		 * Specify a limit and an offset.
		 * 
		 * @param int $limit The limit.
		 * @param int $offset The offset.
		 */
		function __construct($limit = 25, $offset = 0)
		{
			$this->limit = (int)$limit;
			$this->offset = (int)$offset;
		}
		
		function __toString()
		{
			return "limit {$this->offset}, {$this->limit}";
		}
	}
	
	/**
	 * @class OrderQueryComponent
	 * Order the query results.
	 * @author Marcus Povey
	 */
	class OrderQueryComponent extends QueryComponent
	{
		function __construct($table, $field, $order = "asc")
		{
			global $CONFIG;
			
			$this->table = $CONFIG->dbprefix . sanitise_string($table);
			$this->field = sanitise_string($field);
			$this->order = sanitise_string($order);
		}
		
		function __toString()
		{
			return "order by {$this->table}.{$this->field} {$this->order}";
		}
	}
	
	/**
	 * @class TableQueryComponent
	 * List of tables to select from or insert into.
	 * @author Marcus Povey
	 */
	class TableQueryComponent extends QueryComponent
	{
		function __construct($table)
		{
			global $CONFIG;
			
			$this->table = $CONFIG->dbprefix . sanitise_string($table);
		}
		
		function __toString()
		{
			return $this->table;
		}
	}
	
	/**
	 * @class AccessControlQueryComponent
	 * Access control component.
	 * @author Marcus Povey
	 */
	class AccessControlQueryComponent extends QueryComponent
	{
		/**
		 * Construct the ACL.
		 * 
		 * @param string $acl_table The table where the access control field is.
		 * @param string $acl_field The field containing the access control.
		 * @param string $object_owner_table The table containing the owner information for the stuff you're retrieving.
		 * @param string $object_owner_id_field The field in $object_owner_table containing the owner information
		 */
		function __construct($acl_table = "entities", $acl_field = "access_id", $object_owner_table = "entities", $object_owner_id_field = "owner_guid")
		{
			global $CONFIG;
			
			$this->acl_table = $CONFIG->dbprefix . sanitise_string($acl_table);
			$this->acl_field = sanitise_string($acl_field);
			$this->object_owner_table = $CONFIG->dbprefix . sanitise_string($object_owner_table);
			$this->object_owner_id_field = sanitise_string($object_owner_id_field);
		}
		
		function __toString()
		{
			$access = get_access_list();
			
			return "and ({$this->acl_table}.{$this->acl_field} in {$access} or ({$this->acl_table}.{$this->acl_field} = 0 and {$this->object_owner_table}.{$this->object_owner_id_field} = {$_SESSION['id']}))";
		}
	}
	
	/**
	 * @class JoinQueryComponent Join query.
	 * Represents a join query.
	 * @author Marcus Povey
	 */
	class JoinQueryComponent extends QueryComponent
	{
		/**
		 * Construct a join query.
		 * @param string $table Table one to join...
		 * @param string $field Field 1 with...
		 * @param string $table2 Table 2 ... 
		 * @param string $field2 Field...
		 * @param string $operator Using this operator
		 */
		function __construct($table1, $field1, $table2, $field2, $operator = "=") 
		{
			global $CONFIG;
			
			$this->table1 = $CONFIG->dbprefix . sanitise_string($table1);
			$this->field1 = sanitise_string($field1);
			$this->table2 = $CONFIG->dbprefix . sanitise_string($table2);
			$this->field2 = sanitise_string($field2);
			$this->operator = sanitise_string($operator);
		}
		
		function __toString() 
		{
			return "join {$this->table2} on {$this->$table}.{$this->$field} {$this->$operator} {$this->$table2}.{$this->$field2}";
		}
	}
	
	/**
	 * @class SetQueryComponent Set query.
	 * Represents an update set query.
	 * @author Marcus Povey
	 */
	class SetQueryComponent extends QueryComponent
	{
		/**
		 * Construct a setting query
		 *
		 * @param string $table The table to modify
		 * @param string $field The field to modify
		 * @param mixed $value The value to set it to
		 */
		function __construct($table, $field, $value)
		{
			global $CONFIG;
			
		 	$this->table = $CONFIG->dbprefix . sanitise_string($table);
		 	$this->field = sanitise_string($field);
		 	if (is_numeric($value))
		 		$this->value = (int)$value;
		 	else
		 		$this->value = "'".sanitise_string($value)."'";
		}
		
		function __toString() 
		{
			return "{$this->table}.{$this->field}={$this->value}";
		}
	}
	
	/**
	 * @class WhereQueryComponent
	 * A component of a where query.
	 * @author Marcus Povey
	 */
	class WhereQueryComponent extends QueryComponent
	{
		/**
		 * A where query.
		 * 
		 * @param string $left_table The table on the left of the operator
		 * @param string $left_field The left field
		 * @param string $operator The operator eg "=" or "<"
		 * @param string $right_table The table on the right of the operator
		 * @param string $right_field The right field
		 * @param string $link_operator How this where clause links with the previous clause, eg. "and" "or"
		 */
		function __construct($left_table, $left_field, $operator, $right_table, $right_field, $link_operator = "and")
		{
			global $CONFIG;
			
			$this->link_operator = sanitise_string($link_operator);
		 	$this->left_table = $CONFIG->dbprefix . sanitise_string($left_table);
		 	$this->left_field = sanitise_string($left_field);
		 	$this->operator = sanitise_string($operator);
		 	$this->right_table = $CONFIG->dbprefix . sanitise_string($right_table);
		 	$this->right_field = sanitise_string($right_field);
		}
		
		/**
		 * Return the SQL without the link operator.
		 */
		public function toStringNoLink()
		{
			return "{$this->left_table }.{$this->left_field} {$this->operator} {$this->right_table}.{$this->right_field}";
		}
		
		function __toString() 
		{
			return "{$this->link_operator} " . $this->toStringNoLink();
		}
	}
	
	/**
	 * @class WhereStaticQueryComponent
	 * A component of a where query where there is no right hand table, rather a static value.
	 * @author Marcus Povey
	 */
	class WhereStaticQueryComponent extends WhereQueryComponent
	{
		/**
		 * A where query.
		 * 
		 * @param string $left_table The table on the left of the operator
		 * @param string $left_field The left field
		 * @param string $operator The operator eg "=" or "<"
		 * @param string $value The value
		 * @param string $link_operator How this where clause links with the previous clause, eg. "and" "or"
		 */
		function __construct($left_table, $left_field, $operator, $value, $link_operator = "and")
		{
			global $CONFIG;
			
			$this->link_operator = sanitise_string($link_operator);
		 	$this->left_table = $CONFIG->dbprefix . sanitise_string($left_table);
		 	$this->left_field = sanitise_string($left_field);
		 	$this->operator = sanitise_string($operator);
		 	if (is_numeric($value))
		 		$this->value = (int)$value;
		 	else
		 		$this->value = "'".sanitise_string($value)."'";
		}
		
		/**
		 * Return the SQL without the link operator.
		 */
		public function toStringNoLink()
		{
			return "{$this->left_table }.{$this->left_field} {$this->operator} {$this->value}";
		}
	}
	
	/**
	 * @class WhereSetQueryComponent
	 * A where query that may contain other where queries (in brackets).
	 * @author Marcus Povey
	 */
	class WhereSetQueryComponent extends WhereQueryComponent
	{
		/**
		 * Construct a subset of wheres.
		 *
		 * @param array $wheres An array of WhereQueryComponent 
		 * @param string $link_operator How this where clause links with the previous clause, eg. "and" "or"
		 */
		function __construct(array $wheres, $link_operator = "and")
		{
			$this->link_operator = sanitise_string($link_operator);
			$this->wheres = $wheres;
		}
		
		public function toStringNoLink()
		{
			$cnt = 0;
			$string = " (";
			foreach ($this->wheres as $where) {
				if (!($where instanceof WhereQueryComponent))
					throw new DatabaseException("Where set contains non WhereQueryComponent");
				
				if (!$cnt)
					$string.= $where->toStringNoLink();
				else
					$string.=" $where ";
				
				$cnt ++;			
			}
			$string .= ")";
			
			return $string;
		}
	}
	
	/**
	 * @class QueryTypeQueryComponent
	 * What type of query is this?
	 * @author Marcus Povey
	 */
	abstract class QueryTypeQueryComponent extends QueryComponent 
	{
		function __toString()
		{
			return $this->query_type; 
		}
	}
	
	/**
	 * @class SelectQueryTypeQueryComponent
	 * A select query.
	 * @author Marcus Povey
	 */
	class SelectQueryTypeQueryComponent extends QueryTypeQueryComponent 
	{
		function __construct() 
		{
			$this->query_type = "select";	
		}
	}
	
	/**
	 * @class InsertQueryTypeQueryComponent
	 * An insert query.
	 * @author Marcus Povey
	 */
	class InsertQueryTypeQueryComponent extends QueryTypeQueryComponent 
	{
		function __construct() 
		{
			$this->query_type = "insert into";	
		}
	}
	
	/**
	 * @class DeleteQueryTypeQueryComponent
	 * A delete query.
	 * @author Marcus Povey
	 */
	class DeleteQueryTypeQueryComponent extends QueryTypeQueryComponent 
	{
		function __construct() 
		{
			$this->query_type = "delete from";	
		}
	}
	
	/**
	 * @class UpdateQueryTypeQueryComponent
	 * An update query.
	 * @author Marcus Povey
	 */
	class UpdateQueryTypeQueryComponent extends QueryTypeQueryComponent 
	{
		function __construct() 
		{
			$this->query_type = "update";	
		}
	}
	
	/**
	 * @class Query
	 * This class provides a framework to construct complex queries in a safe environment.
	 * 
	 * @author Marcus Povey
	 */
	class Query
	{
		
		/// The limit of the query
		private $limit_and_offset; 
		
		/// Fields to return on a query
		private $fields;
		
		/// Tables to use in a from query
		private $tables;
		
		/// Join tables
		private $joins;
		
		/// Set values 
		private $sets;
		
		/// Where query
		private $where;
		
		/// Order by
		private $order;
		
		/// The query type
		private $query_type;
		
		/// ACL
		private $access_control;
		
		/**
		 * Construct query & initialise variables
		 */
		function __construct() 
		{
			$this->fields = array();
			$this->tables = array();
			$this->joins = array();
			$this->where = array();
			$this->sets = array();
			
			$this->setQueryType(new SelectQueryTypeQueryComponent());
		}
		
		public function setLimitAndOffset(LimitOffsetQueryComponent $component) { $this->limit_and_offset = $component; }
		
		public function setSelectField(SelectFieldQueryComponent $component) 
		{
			$this->fields = array();
			return $this->addSelectField($component);
		}
		
		public function addSelectField(SelectFieldQueryComponent $component) { $this->fields[] = $component; }
		
		public function addJoin(JoinQueryComponent $component) { $this->joins[] = $component; }
		
		public function addSet(SetQueryComponent $component) { $this->sets[] = $component; }
		
		public function setQueryType(QueryTypeQueryComponent $component) { $this->query_type = $component; }
		
		public function setOrder(OrderQueryComponent $component) { $this->order = $component; }
		
		public function addTable(TableQueryComponent $component) { $this->tables[] = $component; }
		
		public function addWhere(WhereQueryComponent $component) { $this->where[] = $component; }
		
		public function setAccessControl(AccessControlQueryComponent $component) { $this->access_control = $component; }
		
		public function __toString()
		{
			global $CONFIG;
			
			$sql = "";
			
			try
			{ 
				// Query prefix & fields
				if (!empty($this->query_type))
				{
					$sql .= "{$this->query_type} ";
					
					if (!empty($this->fields))
					{
						$fields = "";
						
						foreach ($this->fields as $field)
							$fields .= "$field";	
						
						$sql .= " $fields from ";
					}
					else
						throw new DatabaseException("Fields missing on a select style query");
				}
				else
					throw new DatabaseException("Unrecognised or unspecified query type.");
						
				// Tables
				if (!empty($this->tables)) 
				{
					foreach($this->tables as $table) 
						$sql .= "$table, ";
						
					$sql = trim($sql, ", ");
				}
				else
					throw new DatabaseException("No tables specified for query.");
				
				// Joins on select queries
				if ($this->query_type->query_type == 'select') 
				{
					if (!empty($this->joins)) 
					{	
						foreach($this->joins as $join) 
							$sql .= "$join ";
					}
				}
				
				// Setting values
				if (
					($this->query_type->query_type == 'update') || 
					($this->query_type->query_type == 'insert')
				) 
				{
					$sql .= "set ";
					
					foreach ($this->sets as $set)
						$sql .= "$set, ";
						
					$sql = trim($sql, ", ") . " ";
				}
				
				// Where
				if (!empty($this->where))
				{
					$sql .= " where 1 ";
					
					foreach ($this->where as $where)
						$sql .= "$where ";
				}
	
				// Access control
				if (!empty($this->access_control)) 
				{
				
					// Catch missing Where
					if (empty($this->where))
						$sql .= " where 1 ";
					
					$sql .= "{$this->access_control} ";
				} 
				else
					throw new DatabaseException("No access control was provided on query");
					
				// Order by
				if (!empty($this->order))
					$sql .= "{$this->order} ";
					
				// Limits
				if (!empty($this->limit_and_offset))
					$sql .= "{$this->limit_and_offset} ";
				
				
				
			} catch (Exception $e) {
				trigger_error($e, E_USER_WARNING);
			}
			
					
			return $sql;
		}
		
	}
	
	/**
	 * @class SimpleQuery
	 * A wrapper for Query which provides simple interface for common functions.
	 * @author Marcus Povey
	 */
	class SimpleQuery extends Query
	{
		function __construct() 
		{
			parent::__construct();
			
			// Set a default query type (select)
			$this->simpleQueryType();
			
			// Set a default access control
			$this->simpleAccessControl();
			
			// Set default limit and offset
			$this->simpleLimitAndOffset();
		}
		
		/**
		 * Set the query type.
		 * 
		 * @param string $type The type of search - available are "select", "update", "delete", "insert".
		 */
		public function simpleQueryType($type = "select")
		{
			$type = strtolower(sanitise_string($type));
			
			switch ($type)
			{
				case "insert" :
					return $this->setQueryType(InsertQueryTypeQueryComponent()); 
				break;
				case "delete" : 
					return $this->setQueryType(DeleteQueryTypeQueryComponent());
				break;
				case "update" :
					 return $this->setQueryType(UpdateQueryTypeQueryComponent());
				break;
				default: return $this->setQueryType(SelectQueryTypeQueryComponent());
			}
		}

		/**
		 * Set a field to query in a select statement.
		 * 
		 * @param string $table Table to query.
		 * @param string $field Field in that table.
		 */
		public function simpleSelectField($table, $field) { return $this->setSelectField(new SelectFieldQueryComponent($table, $field)); }
		
		/**
		 * Add a select field to query in a select statement.
		 * 
		 * @param string $table Table to query.
		 * @param string $field Field in that table. 
		 */
		public function simpleAddSelectField($table, $field) { return $this->addSelectField(new SelectFieldQueryComponent($table, $field)); }
		
		/**
		 * Add a set value to an update query.
		 * 
		 * @param string $table The table to update.
		 * @param string $field The field in the table.
		 * @param mixed $value The value to set it to.
		 */
		public function simpleSet($table, $field, $value) { return $this->addSet(new SetQueryComponent($table, $field, $value)); }
		
		/**
		 * Add a join to the table.
		 * 
		 * @param string $table Table one to join...
		 * @param string $field Field 1 with...
		 * @param string $table2 Table 2 ... 
		 * @param string $field2 Field...
		 * @param string $operator Using this operator 
		 */
		public function simpleJoin($table1, $field1, $table2, $field2, $operator = "=") { return $this->addJoin(new JoinQueryComponent($table1, $field1, $table2, $field2, $operator)); }
		
		/**
		 * Add a table to the query.
		 * 
		 * @param string $table The table.
		 */
		public function simpleTable($table) { return $this->addTable(new TableQueryComponent($table)); }

		/**
		 * Compare one table/field to another table/field.
		 * 
		 * @param string $left_table The table on the left of the operator
		 * @param string $left_field The left field
		 * @param string $operator The operator eg "=" or "<"
		 * @param string $right_table The table on the right of the operator
		 * @param string $right_field The right field
		 * @param string $link_operator How this where clause links with the previous clause, eg. "and" "or"
		 */
		public function simpleWhereOnTable($left_table, $left_field, $operator, $right_table, $right_field, $link_operator = "and") { return $this->addWhere(new WhereQueryComponent($left_table, $left_field, $operator, $right_table, $right_field, $link_operator)); }
		
		/**
		 * Compare one table/field to a value.
		 * 
		 * @param string $left_table The table on the left of the operator
		 * @param string $left_field The left field
		 * @param string $operator The operator eg "=" or "<"
		 * @param string $value The value
		 * @param string $link_operator How this where clause links with the previous clause, eg. "and" "or"
		 */
		public function simpleWhereOnValue($left_table, $left_field, $operator, $value, $link_operator = "and") { return $this->addWhere(new WhereStaticQueryComponent($left_table, $left_field, $operator, $value, $link_operator)); }
		
		/**
		 * Set access control.
		 * 
		 * @param string $acl_table The table where the access control field is.
		 * @param string $acl_field The field containing the access control.
		 * @param string $object_owner_id_field The field in $object_owner_table containing the owner information.
		 */
		public function simpleAccessControl($acl_table = "entities", $acl_field = "access_id", $object_owner_id_field = "owner_guid") { return $this->setAccessControl(new AccessControlQueryComponent($acl_table, $acl_field, $acl_table, $object_owner_id_field)); }

		/**
		 * Set the limit and offset.
		 * 
		 * @param int $limit The limit.
		 * @param int $offset The offset.
		 */
		public function simpleLimitAndOffset($limit = 25, $offset = 0) { return $this->setLimitAndOffset(new LimitOffsetQueryComponent($limit, $offset)); }
		
		/**
		 * Set the order query.
		 * 
		 * @param string $table The table to query
		 * @param string $field The field to query
		 * @param string $order Order the query
		 */
		public function simpleOrder($table, $field, $order = "desc") 
		{
			$table = sanitise_string($table);
			$field = sanitise_string($field);
			$order = strtolower(sanitise_string($order));
			 
			return $this->setOrder(new OrderQueryComponent($table, $field, $order)); break;
		}
	}
	
	/**
	 * Connect to the database server and use the Elgg database for a particular database link
	 *
	 * @param string $dblinkname Default "readwrite"; you can change this to set up additional global database links, eg "read" and "write" 
	 */
		function establish_db_link($dblinkname = "readwrite") {
			
			// Get configuration, and globalise database link
		        global $CONFIG, $dblink;
		        
		        if (!isset($dblink)) {
		        	$dblink = array();
		        }
		        
		        if ($dblinkname != "readwrite" && isset($CONFIG->db[$dblinkname])) {
		        	if (is_array($CONFIG->db[$dblinkname])) {
		        		$index = rand(0,sizeof($CONFIG->db[$dblinkname]));
		        		$dbhost = $CONFIG->db[$dblinkname][$index]->dbhost;
						$dbuser = $CONFIG->db[$dblinkname][$index]->dbuser;
						$dbpass = $CONFIG->db[$dblinkname][$index]->dbpass;
						$dbname = $CONFIG->db[$dblinkname][$index]->dbname;
		        	} else {
						$dbhost = $CONFIG->db[$dblinkname]->dbhost;
						$dbuser = $CONFIG->db[$dblinkname]->dbuser;
						$dbpass = $CONFIG->db[$dblinkname]->dbpass;
						$dbname = $CONFIG->db[$dblinkname]->dbname;
		        	}
		        } else {
		        	$dbhost = $CONFIG->dbhost;
					$dbuser = $CONFIG->dbuser;
					$dbpass = $CONFIG->dbpass;
					$dbname = $CONFIG->dbname;
		        }
		        
		    // Connect to database
		        if (!$dblink[$dblinkname] = mysql_connect($CONFIG->dbhost, $CONFIG->dbuser, $CONFIG->dbpass, true))
		        	throw new DatabaseException("Elgg couldn't connect to the database using the given credentials.");
		        if (!mysql_select_db($CONFIG->dbname, $dblink[$dblinkname]))
		        	throw new DatabaseException("Elgg couldn't select the database {$CONFIG->dbname}.");
			
		}
		
	/**
	 * Establish all database connections
	 * 
	 * If the configuration has been set up for multiple read/write databases, set those
	 * links up separately; otherwise just create the one database link
	 *
	 */
		
		function setup_db_connections() {
			
			// Get configuration and globalise database link
				global $CONFIG, $dblink;
				
				if (!empty($CONFIG->db->split)) {
					establish_db_link('read');
					establish_db_link('write');
				} else {
					establish_db_link('readwrite');
				}
			
		}
		
	/**
	 * Alias to setup_db_connections, for use in the event handler
	 *
	 * @param string $event The event type
	 * @param string $object_type The object type
	 * @param mixed $object Used for nothing in this context
	 */
		function init_db($event, $object_type, $object = null) {
			setup_db_connections();
			return true;
		}
		
	/**
	 * Gets the appropriate db link for the operation mode requested
	 *
	 * @param string $dblinktype The type of link we want - "read", "write" or "readwrite" (the default)
	 * @return object Database link
	 */
		function get_db_link($dblinktype) {
			
			global $dblink;
			
			if (isset($dblink[$dblinktype])) {
				return $dblink[$dblinktype];
			} else {
				return $dblink['readwrite'];
			}
			
		}
		
		/**
		 * Explain a given query, useful for debug.
		 */
		function explain_query($query, $link)
		{
			if ($result = mysql_query("explain " . $query, $link)) {
                return mysql_fetch_object($result);
            }
            
            return false;
		}
		
	/**
     * Use this function to get data from the database
     * @param mixed $query The query being passed.
     * @param string $call Optionally, the name of a function to call back to on each row (which takes $row as a single parameter)
     * @return array An array of database result objects
     */
    
        function get_data($query, $callback = "") {
            
            global $CONFIG, $dbcalls;
            
            if (!callpath_gatekeeper($CONFIG->path . "engine/", true, true))
            	throw new DatabaseException("Access to privileged function 'get_data()' is denied.");
            
            $dblink = get_db_link('read');
            
            $resultarray = array();
            $dbcalls++;
            
        	if ((isset($CONFIG->debug)) && ($CONFIG->debug==true))
            {
            	error_log("--- DB QUERY --- $query");
            	error_log("--- EXPLAINATION --- " . print_r(explain_query($query,$dblink), true));
            }
            
            if ($result = mysql_query("$query", $dblink)) {
                while ($row = mysql_fetch_object($result)) {
                	if (!empty($callback) && is_callable($callback)) {
                		$row = $callback($row);
                	}
                    $resultarray[] = $row;
                }
            }
            
            if (mysql_errno($dblink))
				throw new DatabaseException(mysql_error($dblink) . " QUERY: " . $query);
				
       		if (empty($resultarray)) {
       			if ((isset($CONFIG->debug)) && ($CONFIG->debug==true))
       				error_log("WARNING: DB query \"$query\" returned no results.");
       				
                return false;
            }
            return $resultarray;
        }
        
    /**
     * Use this function to get a single data row from the database
     * @param mixed $query The query to run.
     * @return object A single database result object
     */ 
    
        function get_data_row($query) {
            
            global $CONFIG, $dbcalls;
            
            if (!callpath_gatekeeper($CONFIG->path . "engine/", true, true))
            	throw new DatabaseException("Access to privileged function 'get_data_row()' is denied.");
            
            $dblink = get_db_link('read');
            
            $dbcalls++;
            
        	if ((isset($CONFIG->debug)) && ($CONFIG->debug==true))
            {
            	error_log("--- DB QUERY --- $query");
            	error_log("--- EXPLAINATION --- " . print_r(explain_query($query,$dblink), true));
            }
            
            if ($result = mysql_query("$query", $dblink)) {
                while ($row = mysql_fetch_object($result)) {
                    return $row;
                }
            }
            
            if (mysql_errno($dblink))
				throw new DatabaseException(mysql_error($dblink) . " QUERY: " . $query);
            
			if ((isset($CONFIG->debug)) && ($CONFIG->debug==true))
       				error_log("WARNING: DB query \"$query\" returned no results.");
       				
            return false;
        }
        
    /**
     * Use this function to insert database data; returns id or false
     * 
     * @param mixed $query The query to run.
     * @return int $id the database id of the inserted row.
     */ 
    
        function insert_data($query) {
            
            global $CONFIG, $dbcalls;
            
            if (!callpath_gatekeeper($CONFIG->path . "engine/", true, true))
            	throw new DatabaseException("Access to privileged function 'insert_data()' is denied.");
            
            $dblink = get_db_link('write');
            
            $dbcalls++;
            
            if (mysql_query("$query", $dblink)) 
                return mysql_insert_id($dblink);
                
			if (mysql_errno($dblink))
				throw new DatabaseException(mysql_error($dblink) . " QUERY: " . $query);
                
			return false;
        }
        
    /**
     * Update database data
     * 
     * @param mixed $query The query to run.
     * @return int|false Either the number of affected rows, or false on failure
     */ 
    
        function update_data($query) {
            
            global $dbcalls, $CONFIG;
            
            if (!callpath_gatekeeper($CONFIG->path . "engine/", true, true))
            	throw new DatabaseException("Access to privileged function 'update_data()' is denied.");
            
            $dblink = get_db_link('write');
            
            $dbcalls++;
            
            if (mysql_query("$query", $dblink))
            	return mysql_affected_rows();
            	
           	if (mysql_errno($dblink))
				throw new DatabaseException(mysql_error($dblink) . " QUERY: " . $query);
         
         	return false;   
            
        }

	/**
	 * Use this function to delete data
	 *
	 * @param mixed $query The SQL query to run
	 * @return int|false Either the number of affected rows, or false on failure
	 */
    
        function delete_data($query) {
            
            global $dbcalls, $CONFIG;
            
            if (!callpath_gatekeeper($CONFIG->path . "engine/", true, true))
            	throw new DatabaseException("Access to privileged function 'delete_data()' is denied.");
            
            $dblink = get_db_link('write');
            
            $dbcalls++;
            
            if (mysql_query("$query", $dblink)) 
                return mysql_affected_rows();
            
            if (mysql_errno($dblink))
				throw new DatabaseException(mysql_error($dblink) . " QUERY: " . $query);
                
			return false;      
        }
    
   /**
    * Returns the number of rows returned by the last select statement, without the need to re-execute the query.
    *
    * CANDIDATE FOR DELETION?
    * 
    * @return int The number of rows returned by the last statement
    */
		function count_last_select() {
        	$row = get_data_row("SELECT found_rows() as count");
        	if ($row)
        		return $row->count;
        	return 0;
        }
 
	/**
	 * Get the tables currently installed in the Elgg database
	 *
	 * @return array List of tables
	 */
        function get_db_tables() {
        	global $CONFIG;
        	$result = get_data("show tables");
        	        	 	
        	$tables = array();
        	
        	if (is_array($result) && !empty($result)) {
        		foreach($result as $row) {
        			$row = (array) $row;
        			if (is_array($row) && !empty($row))
	        			foreach($row as $element) {
	        				$tables[] = $element;
	        			}
        		}
        	}
        	else
        		return false;
        	
        	return $tables;
        }
        
	/**
	 * Get the last database error for a particular database link
	 *
	 * @param database link $dblink
	 * @return string Database error message
	 */
        function get_db_error($dblink) {
        	return mysql_error($dblink);
        }
        
	/**
	 * Runs a full database script from disk
	 *
	 * @uses $CONFIG
	 * @param string $scriptlocation The full path to the script
	 */
        function run_sql_script($scriptlocation) {
        	
        	if ($script = file_get_contents($scriptlocation)) {

        		global $CONFIG;
        		
        		$errors = array();
        		
        		$script = preg_replace('/\-\-.*\n/', '', $script);
        		$sql_statements =  preg_split('/;[\n\r]+/', $script);
        		foreach($sql_statements as $statement) {
        			$statement = trim($statement);
        			$statement = str_replace("prefix_",$CONFIG->dbprefix,$statement);
        			if (!empty($statement)) {
        				$result = update_data($statement);
        			}
        		}
        		if (!empty($errors)) {
        			$errortxt = "";
        			foreach($errors as $error)
        				$errortxt .= " {$error};";
        			throw new DatabaseException("There were a number of issues: " . $errortxt);
        		}
        		
        	} else {
        		throw new DatabaseException("Elgg couldn't find the requested database script at {$scriptlocation}.");
        	}
        	
        }
        
	/**
	 * Sanitise a string for database use
	 *
	 * @param string $string The string to sanitise
	 * @return string Sanitised string
	 */
        function sanitise_string($string) {
        	return mysql_real_escape_string(trim($string));
        }
        
	/**
	 * Wrapper function for Americans
	 *
	 * @param string $string The string to sanitise
	 * @return string Sanitised string
	 * @uses sanitise_string
	 */
        function sanitize_string($string) {
        	return sanitise_string($string);
        }
        
	/**
	 * Sanitises an integer for database use
	 *
	 * @param int $int
	 * @return int Sanitised integer
	 */
        function sanitise_int($int) {
        	return (int) $int;
        }
        
	/**
	 * Wrapper function for Americans
	 *
	 * @param int $int
	 * @return int Sanitised integer
	 * @uses sanitise_string
	 */
        function sanitize_int($int) {
        	return (int) $int;
        }
        
	// Stuff for initialisation

		register_event_handler('boot','system','init_db',0);

?>