iPhone的sqlite应用程序可以附加到其他数据库？

Question

ATTACH DATABASE命令可用于在sqlite数据库文件之间传输行，并允许您从数据库的表（例如，

$ sqlite3 BookLoansDB.sqlite 
sqlite> ATTACH DATABASE '/Users/.../Documents/BooksDB.sqlite' AS books_db; 
sqlite> select B.BookName, B.Pages, BL.LentTo from main.tblBookLoan BL inner join books_db.tblBook B on B.BookID = BL.BookID; 
The Client|512|Jenny 
The Pelican Brief|432|Mike 

如何从iPhone上的objective-c执行相同的操作。这种代码我没有成功：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentDirectory = [paths objectAtIndex:0]; 
const char *booksDBPath = [[documentDirectory stringByAppendingPathComponent:@"BooksDB.sqlite"] UTF8String]; 
const char *bookLoansDBPath = [[documentDirectory stringByAppendingPathComponent:@"BookLoansDB.sqlite"] UTF8String]; 
sqlite3 *bookLoansDB; 
int result = sqlite3_open(bookLoansDBPath, &bookLoansDB); 
sqlite3_stmt *attachStmt; 
NSString *attachSQL = [NSString stringWithFormat: @"ATTACH DATABASE \'%s\' AS books_db", bookLoansDBPath]; 
result = sqlite3_prepare_v2(bookLoansDB, [attachSQL UTF8String] , -1, &attachStmt, nil); 
char *errorMessage; 
result = sqlite3_exec(bookLoansDB, [attachSQL UTF8String], NULL, NULL, &errorMessage); 
sqlite3_stmt *selectStmt; 
NSString *selectSQL = @"select * from main.tblBookLoan BL inner join books_db.tblBook B on B.BookID = BL.BookID"; 
result = sqlite3_prepare_v2(bookLoansDB, [selectSQL UTF8String] , -1, &selectStmt, nil); 
// result == 1 
result = sqlite3_step(selectStmt) ; 
// result == 21 
if (result == SQLITE_ROW) 
{ 
    //do something 
} 

它可以完成吗？

Answer 1

您可以在iPhone上的sqlite中附加数据库。很难说这是怎么回事你的代码，但它应该帮助，如果它看起来更像这样一点：

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentDirectory = [paths objectAtIndex:0]; 
const char *booksDBPath = [[documentDirectory stringByAppendingPathComponent:@"BooksDB.sqlite"] UTF8String]; 
const char *bookLoansDBPath = [[documentDirectory stringByAppendingPathComponent:@"BookLoansDB.sqlite"] UTF8String]; 
sqlite3 *bookLoansDB; 
if (sqlite3_open(bookLoansDBPath, &bookLoansDB) == SQLITE_OK) { 
    NSString *attachSQL = [NSString stringWithFormat: @"ATTACH DATABASE \'%s\' AS books_db", bookLoansDBPath]; 
    char *errorMessage; 
    if (sqlite3_exec(bookLoansDB, [attachSQL UTF8String], NULL, NULL, &errorMessage) == SQLITE_OK && errorMessage == nil) { 
     sqlite3_stmt *selectStmt; 
     NSString *selectSQL = @"select * from main.tblBookLoan BL inner join books_db.tblBook B on B.BookID = BL.BookID"; 
     if (sqlite3_prepare_v2(bookLoansDB, [selectSQL UTF8String] , -1, &selectStmt, nil) == SQLITE_OK) { 
      while (sqlite3_step(selectStmt) == SQLITE_ROW) { 
       //process row 
      } 
     } 
     else { 
      NSLog(@"Error while creating select statement: '%s'", sqlite3_errmsg(bookLoansDB)); 
     } 
    } 
    else { 
     NSLog(@"Error while attaching databases: '%s'", errorMessage); 
    } 
} 
else { 
    NSLog(@"Failed to open database at %@ with error %s", booksDBPath, sqlite3_errmsg(bookLoansDB)); 
    sqlite3_close(bookLoansDB); 
} 

我没有测试此代码，只需修改你的，所以它可能需要修正。

Answer 2

我已经得到了工作示例（将我的数据库名称混入“附加数据库”SQL中）。所以是的，它可以做到。感谢您指点我正确的方向Deepmist

由于这样的例子很难找到，我粘贴了下面的工作版本。

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
NSString *documentDirectory = [paths objectAtIndex:0]; 
const char *booksDBPath = [[documentDirectory stringByAppendingPathComponent:@"BooksDB.sqlite"] UTF8String]; 
const char *bookLoansDBPath = [[documentDirectory stringByAppendingPathComponent:@"BookLoansDB.sqlite"] UTF8String]; 
sqlite3 *bookLoansDB; 
if (sqlite3_open(bookLoansDBPath, &bookLoansDB) == SQLITE_OK) { 
    NSString *attachSQL = [NSString stringWithFormat: @"ATTACH DATABASE \'%s\' AS books_db", booksDBPath]; 
    char *errorMessage; 
    if (sqlite3_exec(bookLoansDB, [attachSQL UTF8String], NULL, NULL, &errorMessage) == SQLITE_OK) { 
     sqlite3_stmt *selectStmt; 
     NSString *selectSQL = @"select * from main.tblBookLoan BL inner join books_db.tblBook B on B.BookID = BL.BookID"; 
     if (sqlite3_prepare_v2(bookLoansDB, [selectSQL UTF8String] , -1, &selectStmt, nil) == SQLITE_OK) { 
      int n=0; 
      while (sqlite3_step(selectStmt) == SQLITE_ROW) { 
       //do something 
      } 
     } 
     else { 
      NSLog(@"Error while creating select statement: '%s'", sqlite3_errmsg(bookLoansDB)); 
     } 
    } 
    else { 
     NSLog(@"Error while attaching databases: '%s'", errorMessage); 
    } 
} 
else { 
    NSLog(@"Failed to open database at %@ with error %s", booksDBPath, sqlite3_errmsg(bookLoansDB)); 
    sqlite3_close(bookLoansDB); 
}