FMDataBase 打开sqlite的外键约束功能

//create databaseNSString* dbPath =[(NSArray*)NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES) objectAtIndex:0];
dbPath =[dbPath stringByAppendingPathComponent:@"test.db"];
db =[FMDatabase databaseWithPath:dbPath];if([db open]){NSLog(@"Database %@ opened", dbPath);//check for foreign_keyNSString* sql =@"PRAGMA foreign_keys";FMResultSet*rs =[db executeQuery:sql];int enabled;if([rs next]){
        enabled =[rs intForColumnIndex:0];}[rs close];if(!enabled){// enable foreign_key
        sql =@"PRAGMA foreign_keys = ON;";[db executeUpdate:sql];// check if successful
        sql =@"PRAGMA foreign_keys";FMResultSet*rs =[db executeQuery:sql];if([rs next]){
            enabled =[rs intForColumnIndex:0];}[rs close];}// do your stuff here, or just cache the connection}else{NSLog(@"Failed to open %@", dbPath);}