如何从存储在sqlite中的NSData中检索字符串? [英] How to retrieve string from NSData stored in sqlite?
问题描述
注意:
- 我已存储
NSData
在本地数据库中。 - 我想从本地数据库中使用它。但由于它作为文本存储在
本地数据库中,因此将问题转换回
NSData
。 - strDbData是
NSString
类型的对象。
- I have stored
NSData
in local database. - I want to use it back from local database. But as it is stored in
local database as text ,facing issue in converting back it into
NSData
. - strDbData is object of type
NSString
here.
我有一个 NSData
存储在本地数据库中,如< a3829c97 3b1efacb c7680f7e 7e7a95a2>
I have one NSData
stored in local database like <a3829c97 3b1efacb c7680f7e 7e7a95a2>
现在我想回复它,所以我按照下面的说法进行操作,但收到错误。
Now I want to retrive it back, so I am doing as mentioned below but I am receiving error.
1)第一种方式
NSData *myData = (NSData*)strDbData;
NSLog(@"%@",[myData class]);
错误: - [__ NSCFString AES256DecryptWithKey:]:无法识别的选择器发送到实例0x1ddcd9c0
2)第二种方式
NSData *myData = [[NSData alloc]initWithData:(NSData*)strDbData];
错误: - [__ NSCFString bytes]:无法识别的选择器发送到实例0x1dd61a40
那么如何将 NSData
转换为本地数据库中的'text'作为'text'返回 NSData
?
So how do I convert NSData
sotred in local database as 'text' back into NSData
?
编辑
strDbData = [[NSString alloc] initWithUTF8String:(const char *) sqlite3_column_text(statement, 6)];
编辑2 在数据库中存储NSData
EDIT 2 Storing NSData in database
-(BOOL)updateSingleRow:(NSData*)myData
{
@try
{
BOOL success = NO;
sqlite3_stmt *statement;
const char *stmt = [[NSString stringWithFormat:@"UPDATE ABC SET XYZ = '%@' WHERE ID = 1 ",myData] UTF8String];
if (sqlite3_open([databaseFilePath UTF8String], &database) == SQLITE_OK)
{
if(sqlite3_prepare_v2(database, stmt, -1, &statement, NULL) == SQLITE_OK)
{
if(sqlite3_step(statement) != SQLITE_DONE )
{
NSLog( @"updateSingleRow Error: %s", sqlite3_errmsg(database) );
}
else if (sqlite3_total_changes(database)>0)
{
success = YES;
}
else if (sqlite3_total_changes(database)==0)
{
NSLog(@"No Updates : %@" , query);
}
}
sqlite3_finalize(statement);
sqlite3_close(database);
}
return success;
}
@catch (NSException *exception)
{
TRACE_ERROR(@"updateSingleRow", exception.name, exception.description);
}
}
推荐答案
如果SQLite列包含二进制数据,您应该通过
If the SQLite column contains binary data, you should read it back via
const void *bytes = sqlite3_column_blob(statement, 6);
int length = sqlite3_column_bytes(statement, 6);
NSData *myData = [[NSData alloc] initWithBytes:bytes length:length];
而不是将其读入字符串。
instead of reading it into a string.
要存储二进制数据,请使用预准备语句。 (我没有测试这段代码,我希望
它是正确的!)
To store binary data, use a "prepared statement". (I did not test this code, I hope that it is correct!)
const char *stmt = "UPDATE ABC SET XYZ = ? WHERE ID = 1";
if (sqlite3_prepare_v2(database, stmt, -1, &statement, NULL) == SQLITE_OK) {
sqlite3_bind_blob(statement, 1, [myData bytes], [myData length], NULL);
// ...
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