]> git.saurik.com Git - wxWidgets.git/blame_incremental - include/wx/db.h
a more easy to use version of wxGetHomeDir() added
[wxWidgets.git] / include / wx / db.h
... / ...
CommitLineData
1///////////////////////////////////////////////////////////////////////////////
2// Name: db.h
3// Purpose: Header file wxDB class. The wxDB class represents a connection
4// to an ODBC data source. The wxDB class allows operations on the data
5// source such as opening and closing the data source.
6// Author: Doug Card
7// Modified by:
8// Mods: Dec, 1998:
9// -Added support for SQL statement logging and database cataloging
10// April, 1999
11// -Added QUERY_ONLY mode support to reduce default number of cursors
12// -Added additional SQL logging code
13// -Added DEBUG-ONLY tracking of Ctable objects to detect orphaned DB connections
14// -Set ODBC option to only read committed writes to the DB so all
15// databases operate the same in that respect
16//
17// Created: 9.96
18// RCS-ID: $Id$
19// Copyright: (c) 1996 Remstar International, Inc.
20// Licence: wxWindows licence, plus:
21// Notice: This class library and its intellectual design are free of charge for use,
22// modification, enhancement, debugging under the following conditions:
23// 1) These classes may only be used as part of the implementation of a
24// wxWindows-based application
25// 2) All enhancements and bug fixes are to be submitted back to the wxWindows
26// user groups free of all charges for use with the wxWindows library.
27// 3) These classes may not be distributed as part of any other class library,
28// DLL, text (written or electronic), other than a complete distribution of
29// the wxWindows GUI development toolkit.
30//
31///////////////////////////////////////////////////////////////////////////////
32
33/*
34// SYNOPSIS START
35// SYNOPSIS STOP
36*/
37
38#ifndef DB_DOT_H
39#define DB_DOT_H
40
41// Use this line for wxWindows v1.x
42//#include "wx_ver.h"
43// Use this line for wxWindows v2.x
44#include "wx/version.h"
45
46#if wxMAJOR_VERSION == 2
47 #ifdef __GNUG__
48 #pragma interface "db.h"
49 #endif
50#endif
51
52#if defined(wx_msw) || defined(__WXMSW__) || defined(WIN32)
53#include <windows.h>
54#endif
55
56#ifdef __UNIX__
57#if wxMAJOR_VERSION == 2
58 extern "C" {
59 #include "../../src/iodbc/isql.h"
60 #include "../../src/iodbc/isqlext.h"
61 }
62#else // version == 1
63 extern "C" {
64 #include "iodbc.h"
65 #include "isqlext.h"
66 }
67#endif
68 typedef float SFLOAT;
69 typedef double SDOUBLE;
70 typedef unsigned int UINT;
71 #define ULONG UDWORD
72#elif defined(__WXMAC__)
73 extern "C" {
74 #include "../../src/iodbc/isql.h"
75 #include "../../src/iodbc/isqlext.h"
76 }
77 typedef float SFLOAT;
78 typedef double SDOUBLE;
79 typedef unsigned int UINT;
80 #define ULONG UDWORD
81#else // msw
82 #define ODBCVER 0x0250
83 #include <sql.h>
84 #include <sqlext.h>
85#endif
86
87#ifdef __UNIX__
88/*
89# ifndef strnicmp
90# define strnicmp strncasecmp
91# endif
92# ifndef stricmp
93# define stricmp strcasecmp
94# endif
95*/
96#elif defined(__WXMAC__)
97#else
98# include <io.h>
99#endif
100
101enum enumDummy {enumDum1};
102
103#define SQL_C_BOOLEAN(datatype) (sizeof(datatype) == 1 ? SQL_C_UTINYINT : (sizeof(datatype) == 2 ? SQL_C_USHORT : SQL_C_ULONG))
104// #define SQL_C_BOOLEAN (sizeof(Bool) == 2 ? SQL_C_USHORT : SQL_C_ULONG)
105
106#define SQL_C_ENUM (sizeof(enumDummy) == 2 ? SQL_C_USHORT : SQL_C_ULONG)
107
108#ifndef TRUE
109#define TRUE 1
110#endif
111
112#ifndef FALSE
113#define FALSE 0
114#endif
115
116const int DB_PATH_MAX = 254;
117
118// Database Globals
119const int DB_TYPE_NAME_LEN = 40;
120const int DB_MAX_STATEMENT_LEN = 2048;
121const int DB_MAX_WHERE_CLAUSE_LEN = 1024;
122const int DB_MAX_ERROR_MSG_LEN = 512;
123const int DB_MAX_ERROR_HISTORY = 5;
124const int DB_MAX_TABLE_NAME_LEN = 128;
125const int DB_MAX_COLUMN_NAME_LEN = 128;
126
127const int DB_DATA_TYPE_VARCHAR = 1;
128const int DB_DATA_TYPE_INTEGER = 2;
129const int DB_DATA_TYPE_FLOAT = 3;
130const int DB_DATA_TYPE_DATE = 4;
131
132const int DB_SELECT_KEYFIELDS = 1;
133const int DB_SELECT_WHERE = 2;
134const int DB_SELECT_MATCHING = 3;
135const int DB_SELECT_STATEMENT = 4;
136
137const int DB_UPD_KEYFIELDS = 1;
138const int DB_UPD_WHERE = 2;
139
140const int DB_DEL_KEYFIELDS = 1;
141const int DB_DEL_WHERE = 2;
142const int DB_DEL_MATCHING = 3;
143
144const int DB_WHERE_KEYFIELDS = 1;
145const int DB_WHERE_MATCHING = 2;
146
147const int DB_GRANT_SELECT = 1;
148const int DB_GRANT_INSERT = 2;
149const int DB_GRANT_UPDATE = 4;
150const int DB_GRANT_DELETE = 8;
151const int DB_GRANT_ALL = DB_GRANT_SELECT | DB_GRANT_INSERT | DB_GRANT_UPDATE | DB_GRANT_DELETE;
152
153// ODBC Error codes (derived from ODBC SqlState codes)
154enum ODBC_ERRORS
155{
156 DB_FAILURE = 0,
157 DB_SUCCESS = 1,
158 DB_ERR_NOT_IN_USE,
159 DB_ERR_GENERAL_WARNING, // SqlState = '01000'
160 DB_ERR_DISCONNECT_ERROR, // SqlState = '01002'
161 DB_ERR_DATA_TRUNCATED, // SqlState = '01004'
162 DB_ERR_PRIV_NOT_REVOKED, // SqlState = '01006'
163 DB_ERR_INVALID_CONN_STR_ATTR, // SqlState = '01S00'
164 DB_ERR_ERROR_IN_ROW, // SqlState = '01S01'
165 DB_ERR_OPTION_VALUE_CHANGED, // SqlState = '01S02'
166 DB_ERR_NO_ROWS_UPD_OR_DEL, // SqlState = '01S03'
167 DB_ERR_MULTI_ROWS_UPD_OR_DEL, // SqlState = '01S04'
168 DB_ERR_WRONG_NO_OF_PARAMS, // SqlState = '07001'
169 DB_ERR_DATA_TYPE_ATTR_VIOL, // SqlState = '07006'
170 DB_ERR_UNABLE_TO_CONNECT, // SqlState = '08001'
171 DB_ERR_CONNECTION_IN_USE, // SqlState = '08002'
172 DB_ERR_CONNECTION_NOT_OPEN, // SqlState = '08003'
173 DB_ERR_REJECTED_CONNECTION, // SqlState = '08004'
174 DB_ERR_CONN_FAIL_IN_TRANS, // SqlState = '08007'
175 DB_ERR_COMM_LINK_FAILURE, // SqlState = '08S01'
176 DB_ERR_INSERT_VALUE_LIST_MISMATCH, // SqlState = '21S01'
177 DB_ERR_DERIVED_TABLE_MISMATCH, // SqlState = '21S02'
178 DB_ERR_STRING_RIGHT_TRUNC, // SqlState = '22001'
179 DB_ERR_NUMERIC_VALUE_OUT_OF_RNG, // SqlState = '22003'
180 DB_ERR_ERROR_IN_ASSIGNMENT, // SqlState = '22005'
181 DB_ERR_DATETIME_FLD_OVERFLOW, // SqlState = '22008'
182 DB_ERR_DIVIDE_BY_ZERO, // SqlState = '22012'
183 DB_ERR_STR_DATA_LENGTH_MISMATCH, // SqlState = '22026'
184 DB_ERR_INTEGRITY_CONSTRAINT_VIOL, // SqlState = '23000'
185 DB_ERR_INVALID_CURSOR_STATE, // SqlState = '24000'
186 DB_ERR_INVALID_TRANS_STATE, // SqlState = '25000'
187 DB_ERR_INVALID_AUTH_SPEC, // SqlState = '28000'
188 DB_ERR_INVALID_CURSOR_NAME, // SqlState = '34000'
189 DB_ERR_SYNTAX_ERROR_OR_ACCESS_VIOL, // SqlState = '37000'
190 DB_ERR_DUPLICATE_CURSOR_NAME, // SqlState = '3C000'
191 DB_ERR_SERIALIZATION_FAILURE, // SqlState = '40001'
192 DB_ERR_SYNTAX_ERROR_OR_ACCESS_VIOL2, // SqlState = '42000'
193 DB_ERR_OPERATION_ABORTED, // SqlState = '70100'
194 DB_ERR_UNSUPPORTED_FUNCTION, // SqlState = 'IM001'
195 DB_ERR_NO_DATA_SOURCE, // SqlState = 'IM002'
196 DB_ERR_DRIVER_LOAD_ERROR, // SqlState = 'IM003'
197 DB_ERR_SQLALLOCENV_FAILED, // SqlState = 'IM004'
198 DB_ERR_SQLALLOCCONNECT_FAILED, // SqlState = 'IM005'
199 DB_ERR_SQLSETCONNECTOPTION_FAILED, // SqlState = 'IM006'
200 DB_ERR_NO_DATA_SOURCE_DLG_PROHIB, // SqlState = 'IM007'
201 DB_ERR_DIALOG_FAILED, // SqlState = 'IM008'
202 DB_ERR_UNABLE_TO_LOAD_TRANSLATION_DLL, // SqlState = 'IM009'
203 DB_ERR_DATA_SOURCE_NAME_TOO_LONG, // SqlState = 'IM010'
204 DB_ERR_DRIVER_NAME_TOO_LONG, // SqlState = 'IM011'
205 DB_ERR_DRIVER_KEYWORD_SYNTAX_ERROR, // SqlState = 'IM012'
206 DB_ERR_TRACE_FILE_ERROR, // SqlState = 'IM013'
207 DB_ERR_TABLE_OR_VIEW_ALREADY_EXISTS, // SqlState = 'S0001'
208 DB_ERR_TABLE_NOT_FOUND, // SqlState = 'S0002'
209 DB_ERR_INDEX_ALREADY_EXISTS, // SqlState = 'S0011'
210 DB_ERR_INDEX_NOT_FOUND, // SqlState = 'S0012'
211 DB_ERR_COLUMN_ALREADY_EXISTS, // SqlState = 'S0021'
212 DB_ERR_COLUMN_NOT_FOUND, // SqlState = 'S0022'
213 DB_ERR_NO_DEFAULT_FOR_COLUMN, // SqlState = 'S0023'
214 DB_ERR_GENERAL_ERROR, // SqlState = 'S1000'
215 DB_ERR_MEMORY_ALLOCATION_FAILURE, // SqlState = 'S1001'
216 DB_ERR_INVALID_COLUMN_NUMBER, // SqlState = 'S1002'
217 DB_ERR_PROGRAM_TYPE_OUT_OF_RANGE, // SqlState = 'S1003'
218 DB_ERR_SQL_DATA_TYPE_OUT_OF_RANGE, // SqlState = 'S1004'
219 DB_ERR_OPERATION_CANCELLED, // SqlState = 'S1008'
220 DB_ERR_INVALID_ARGUMENT_VALUE, // SqlState = 'S1009'
221 DB_ERR_FUNCTION_SEQUENCE_ERROR, // SqlState = 'S1010'
222 DB_ERR_OPERATION_INVALID_AT_THIS_TIME, // SqlState = 'S1011'
223 DB_ERR_INVALID_TRANS_OPERATION_CODE, // SqlState = 'S1012'
224 DB_ERR_NO_CURSOR_NAME_AVAIL, // SqlState = 'S1015'
225 DB_ERR_INVALID_STR_OR_BUF_LEN, // SqlState = 'S1090'
226 DB_ERR_DESCRIPTOR_TYPE_OUT_OF_RANGE, // SqlState = 'S1091'
227 DB_ERR_OPTION_TYPE_OUT_OF_RANGE, // SqlState = 'S1092'
228 DB_ERR_INVALID_PARAM_NO, // SqlState = 'S1093'
229 DB_ERR_INVALID_SCALE_VALUE, // SqlState = 'S1094'
230 DB_ERR_FUNCTION_TYPE_OUT_OF_RANGE, // SqlState = 'S1095'
231 DB_ERR_INF_TYPE_OUT_OF_RANGE, // SqlState = 'S1096'
232 DB_ERR_COLUMN_TYPE_OUT_OF_RANGE, // SqlState = 'S1097'
233 DB_ERR_SCOPE_TYPE_OUT_OF_RANGE, // SqlState = 'S1098'
234 DB_ERR_NULLABLE_TYPE_OUT_OF_RANGE, // SqlState = 'S1099'
235 DB_ERR_UNIQUENESS_OPTION_TYPE_OUT_OF_RANGE, // SqlState = 'S1100'
236 DB_ERR_ACCURACY_OPTION_TYPE_OUT_OF_RANGE, // SqlState = 'S1101'
237 DB_ERR_DIRECTION_OPTION_OUT_OF_RANGE, // SqlState = 'S1103'
238 DB_ERR_INVALID_PRECISION_VALUE, // SqlState = 'S1104'
239 DB_ERR_INVALID_PARAM_TYPE, // SqlState = 'S1105'
240 DB_ERR_FETCH_TYPE_OUT_OF_RANGE, // SqlState = 'S1106'
241 DB_ERR_ROW_VALUE_OUT_OF_RANGE, // SqlState = 'S1107'
242 DB_ERR_CONCURRENCY_OPTION_OUT_OF_RANGE, // SqlState = 'S1108'
243 DB_ERR_INVALID_CURSOR_POSITION, // SqlState = 'S1109'
244 DB_ERR_INVALID_DRIVER_COMPLETION, // SqlState = 'S1110'
245 DB_ERR_INVALID_BOOKMARK_VALUE, // SqlState = 'S1111'
246 DB_ERR_DRIVER_NOT_CAPABLE, // SqlState = 'S1C00'
247 DB_ERR_TIMEOUT_EXPIRED // SqlState = 'S1T00'
248};
249
250struct DbStuff
251{
252 HENV Henv;
253 char Dsn[SQL_MAX_DSN_LENGTH+1]; // Data Source Name
254 char Uid[20+1]; // User ID
255 char AuthStr[20+1]; // Authorization string (password)
256
257 char description[SQL_MAX_DSN_LENGTH+1]; // Not sure what the max length is
258 char fileType[SQL_MAX_DSN_LENGTH+1]; // Not sure what the max length is
259
260 // Optionals needed for some databases like dBase
261 char defaultDir[DB_PATH_MAX]; // Directory that db file resides in
262};
263
264typedef struct
265{
266 char TypeName[DB_TYPE_NAME_LEN];
267 int FsqlType;
268 long Precision;
269 short CaseSensitive;
270// short MinimumScale;
271 short MaximumScale;
272} SqlTypeInfo;
273
274class WXDLLEXPORT CcolInf
275{
276public:
277 char tableName[DB_MAX_TABLE_NAME_LEN+1];
278 char colName[DB_MAX_COLUMN_NAME_LEN+1];
279 int sqlDataType;
280};
281
282enum sqlLog
283{
284 sqlLogOFF,
285 sqlLogON
286};
287
288enum dbms
289{
290 dbmsUNIDENTIFIED,
291 dbmsORACLE,
292 dbmsSYBASE_ASA, // Adaptive Server Anywhere
293 dbmsSYBASE_ASE, // Adaptive Server Enterprise
294 dbmsMS_SQL_SERVER,
295 dbmsMY_SQL,
296 dbmsPOSTGRES,
297 dbmsACCESS,
298 dbmsDBASE,
299 dbmsINFORMIX
300};
301
302typedef enum dbms DBMS;
303
304// The wxDB::errorList is copied to this variable when the wxDB object
305// is closed. This way, the error list is still available after the
306// database object is closed. This is necessary if the database
307// connection fails so the calling application can show the operator
308// why the connection failed. Note: as each wxDB object is closed, it
309// will overwrite the errors of the previously destroyed wxDB object in
310// this variable.
311extern char DBerrorList[DB_MAX_ERROR_HISTORY][DB_MAX_ERROR_MSG_LEN];
312
313class WXDLLEXPORT wxDB
314{
315private:
316
317 // Private data
318 bool dbIsOpen;
319 char *dsn; // Data source name
320 char *uid; // User ID
321 char *authStr; // Authorization string (password)
322 FILE *fpSqlLog; // Sql Log file pointer
323 enum sqlLog sqlLogState; // On or Off
324
325 // Private member functions
326 bool getDbInfo(void);
327 bool getDataTypeInfo(SWORD fSqlType, SqlTypeInfo &structSQLTypeInfo);
328 bool setConnectionOptions(void);
329 void logError(const char *errMsg, const char *SQLState);
330
331 bool fwdOnlyCursors;
332
333public:
334
335 // The following structure contains database information gathered from the
336 // datasource when the datasource is first opened.
337 struct
338 {
339 char dbmsName[40]; // Name of the dbms product
340 char dbmsVer[64]; // Version # of the dbms product
341 char driverName[40]; // Driver name
342 char odbcVer[60]; // ODBC version of the driver
343 char drvMgrOdbcVer[60]; // ODBC version of the driver manager
344 char driverVer[60]; // Driver version
345 char serverName[80]; // Server Name, typically a connect string
346 char databaseName[128]; // Database filename
347 char outerJoins[2]; // Indicates whether the data source supports outer joins
348 char procedureSupport[2]; // Indicates whether the data source supports stored procedures
349 UWORD maxConnections; // Maximum # of connections the data source supports
350 UWORD maxStmts; // Maximum # of HSTMTs per HDBC
351 UWORD apiConfLvl; // ODBC API conformance level
352 UWORD cliConfLvl; // Indicates whether the data source is SAG compliant
353 UWORD sqlConfLvl; // SQL conformance level
354 UWORD cursorCommitBehavior; // Indicates how cursors are affected by a db commit
355 UWORD cursorRollbackBehavior; // Indicates how cursors are affected by a db rollback
356 UWORD supportNotNullClause; // Indicates if data source supports NOT NULL clause
357 char supportIEF[2]; // Integrity Enhancement Facility (Referential Integrity)
358 UDWORD txnIsolation; // Default transaction isolation level supported by the driver
359 UDWORD txnIsolationOptions; // Transaction isolation level options available
360 UDWORD fetchDirections; // Fetch directions supported
361 UDWORD lockTypes; // Lock types supported in SQLSetPos
362 UDWORD posOperations; // Position operations supported in SQLSetPos
363 UDWORD posStmts; // Position statements supported
364 UDWORD scrollConcurrency; // Concurrency control options supported for scrollable cursors
365 UDWORD scrollOptions; // Scroll Options supported for scrollable cursors
366 UDWORD staticSensitivity; // Indicates if additions, deletions and updates can be detected
367 UWORD txnCapable; // Indicates if the data source supports transactions
368 UDWORD loginTimeout; // Number seconds to wait for a login request
369 } dbInf;
370
371 // ODBC handles
372 HENV henv; // ODBC Environment handle
373 HDBC hdbc; // ODBC DB Connection handle
374 HSTMT hstmt; // ODBC Statement handle
375
376 // ODBC Error Inf.
377 char sqlState[20];
378 SDWORD nativeError;
379 char errorMsg[SQL_MAX_MESSAGE_LENGTH];
380 SWORD cbErrorMsg;
381 char errorList[DB_MAX_ERROR_HISTORY][DB_MAX_ERROR_MSG_LEN];
382 int DB_STATUS;
383
384 //Error reporting mode
385 bool silent;
386
387 // Number of Ctable objects connected to this db object
388 unsigned int nTables;
389
390 // Inf. about logical data types VARCHAR, INTEGER, FLOAT and DATE.
391 // This inf. is obtained from the ODBC driver by use of the
392 // SQLGetTypeInfo() function. The key piece of inf. is the
393 // type name the data source uses for each logical data type.
394 // e.g. VARCHAR; Oracle calls it VARCHAR2.
395 SqlTypeInfo typeInfVarchar, typeInfInteger, typeInfFloat, typeInfDate;
396
397 // Public member functions
398 wxDB(HENV &aHenv, bool FwdOnlyCursors=(bool)TRUE);
399 bool Open(char *Dsn, char *Uid, char *AuthStr); // Data Source Name, User ID, Password
400 void Close(void);
401 bool CommitTrans(void);
402 bool RollbackTrans(void);
403 bool DispAllErrors(HENV aHenv, HDBC aHdbc = SQL_NULL_HDBC, HSTMT aHstmt = SQL_NULL_HSTMT);
404 bool GetNextError(HENV aHenv, HDBC aHdbc = SQL_NULL_HDBC, HSTMT aHstmt = SQL_NULL_HSTMT);
405 void DispNextError(void);
406 bool CreateView(const char *viewName, const char *colList, const char *pSqlStmt, bool attemptDrop=TRUE);
407 bool DropView(const char *viewName);
408 bool ExecSql(const char *pSqlStmt);
409 bool GetNext(void);
410 bool GetData(UWORD colNo, SWORD cType, PTR pData, SDWORD maxLen, SDWORD FAR *cbReturned);
411 bool Grant(int privileges, const char *tableName, const char *userList = "PUBLIC");
412 int TranslateSqlState(const char *SQLState);
413 bool Catalog(const char *userID, const char *fileName = "Catalog.txt");
414 CcolInf *GetColumns(char *tableName[], const char *userID=NULL);
415 char *GetDatabaseName(void) {return dbInf.dbmsName;}
416 char *GetDataSource(void) {return dsn;}
417 char *GetUsername(void) {return uid;}
418 char *GetPassword(void) {return authStr;}
419 bool IsOpen(void) {return dbIsOpen;}
420 HENV GetHENV(void) {return henv;}
421 HDBC GetHDBC(void) {return hdbc;}
422 HSTMT GetHSTMT(void) {return hstmt;}
423 bool TableExists(const char *tableName, const char *userID=NULL, const char *path=NULL); // Table name can refer to a table, view, alias or synonym
424 void LogError(const char *errMsg, const char *SQLState = 0) {logError(errMsg, SQLState);}
425 bool SqlLog(enum sqlLog state, const char *filename = "sqllog.txt", bool append = FALSE);
426 bool WriteSqlLog(const char *logMsg);
427 DBMS Dbms(void);
428 bool FwdOnlyCursors(void) {return fwdOnlyCursors;}
429
430}; // wxDB
431
432// This structure forms a node in a linked list. The linked list of "DbList" objects
433// keeps track of allocated database connections. This allows the application to
434// open more than one database connection through ODBC for multiple transaction support
435// or for multiple database support.
436
437struct DbList
438{
439 DbList *PtrPrev; // Pointer to previous item in the list
440 char Dsn[SQL_MAX_DSN_LENGTH+1]; // Data Source Name
441 wxDB *PtrDb; // Pointer to the wxDB object
442 bool Free; // Is item free or in use?
443 DbList *PtrNext; // Pointer to next item in the list
444};
445
446
447#ifdef __WXDEBUG__
448#include "wx/object.h"
449class CstructTablesInUse : public wxObject
450{
451 public:
452 const char *tableName;
453 ULONG tableID;
454 class wxDB *pDb;
455}; // CstructTablesInUse
456#endif
457
458// The following routines allow a user to get new database connections, free them
459// for other code segments to use, or close all of them when the application has
460// completed.
461
462wxDB WXDLLEXPORT *GetDbConnection(DbStuff *pDbStuff, bool FwdOnlyCursors=(bool)TRUE);
463bool WXDLLEXPORT FreeDbConnection(wxDB *pDb);
464void WXDLLEXPORT CloseDbConnections(void);
465int WXDLLEXPORT NumberDbConnectionsInUse(void);
466
467// This function sets the sql log state for all open wxDB objects
468bool SqlLog(enum sqlLog state, const char *filename = "sqllog.txt");
469
470// This routine allows you to query a driver manager
471// for a list of available datasources. Call this routine
472// the first time using SQL_FETCH_FIRST. Continue to call it
473// using SQL_FETCH_NEXT until you've exhausted the list.
474bool WXDLLEXPORT GetDataSource(HENV henv, const char *Dsn, SWORD DsnMax, const char *DsDesc, SWORD DsDescMax,
475 UWORD direction = SQL_FETCH_NEXT);
476
477#endif