ios - sqlite 准备语句 [英] ios - sqlite prepare statement
问题描述
我正在尝试从 ios 应用程序中的 sqlite 数据库读取数据.当我运行应用程序时,它能够打开数据库,但在日志文件中它显示消息 - 准备语句有问题".我不知道我的准备语句有什么问题这是我的代码 -
I am trying to read data from a sqlite database in an ios app. When I run the app, it is able to open the database but in the log file it shows the message - "Problem with the prepare statement". I don't know what is wrong with my prepare statement Here's my code -
-(NSString *)dataFilePath{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
return [documentsDirectory stringByAppendingPathComponent:kFilename];
}
在 viewDidLoad 我有 -
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
myarray = [[NSMutableArray alloc]init];
sqlite3 *database;
if(sqlite3_open([[self dataFilePath]UTF8String], &database)!=SQLITE_OK){
sqlite3_close(database);
NSAssert(0, @"Failed to open database");
}
const char *createSQL = @"SELECT ID, TITLE FROM FIRST ORDER BY TITLE;"; //first is the table in the database
sqlite3_stmt *sqlStmt;
if(sqlite3_prepare_v2(database, [createSQL UTF8String], -1, &sqlStmt, nil)!=SQLITE_OK){
NSLog(@"Problem with prepare statement"); //this is where the code gets stuck and I don't know why
}else{
while(sqlite3_step(sqlStmt)==SQLITE_ROW){
NSInteger number = sqlite3_column_int(sqlStmt, 0);
NSString *title = [NSString stringWithUTF8String:(char *) sqlite3_column_text(sqlStmt, 1)];
[myarray addObject:title];
}
sqlite3_finalize(sqlStmt);
}
sqlite3_close(database);
}
推荐答案
如果您的准备语句失败,而不仅仅是报告准备语句有问题",请尝试检索错误消息,例如,
If your prepare statement fails, rather than just reporting "Problem with prepare statement", try retrieving the error message, e.g.,
NSLog(@"%s Prepare failure '%s' (%1d)", __FUNCTION__, sqlite3_errmsg(database), sqlite3_errcode(database));
这可能会让您更好地指出问题所在.
This might give you a better indication of the problem.
我过去看到的一个问题是,可能找不到数据库(因为它没有包含在包中,名称中有错别字等),但是标准的 sqlite3_open
如果它不存在,函数将创建它,因此 sqlite3_open
将成功,但在新创建的空白数据库中将找不到相关表.比 sqlite3_open
更好的是:
A problem I've seen in the past is that the database might not be found (because it wasn't included in the bundle, typo in the name, etc.) but the standard sqlite3_open
function will create it if it's not there, and thus the sqlite3_open
will succeed, but the table in question won't be found in the blank, newly created database. Better than sqlite3_open
would be:
sqlite3 *database;
if (sqlite3_open_v2([[self dataFilePath] UTF8String], &database, SQLITE_OPEN_READWRITE, NULL) != SQLITE_OK) {
sqlite3_close(database); // not sure you need to close if the open failed
NSAssert(0, @"Failed to open database");
}
这样,如果找不到数据库,您就会收到警告.但是如果你已经完成了sqlite3_open
,你可能有一个空白的数据库,所以你可能想重置你的模拟器和/或从你的设备中删除应用程序,然后再用sqlite3_open_v2代码>.
That way you get a warning if the database is not found. But if you've done sqlite3_open
already, you might have a blank database, so you might want to reset your simulator and/or remove the app from your device, before trying it with sqlite3_open_v2
.
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