ios - 如果 (sqlite3_step(compiledStatement) == SQLITE_ROW) 失败

Question

在第一个实现文件上，所有步骤

- (void) readCitiesFromDatabase {

    databaseName = @"123.sqlite";

    NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDir = [documentPaths objectAtIndex:0];
    databasePath = [documentsDir stringByAppendingPathComponent:databaseName];

    // Setup the database object
    sqlite3 *database;

    // Setup the SQL Statement and compile it for faster access
    NSString *querySQL = [NSString stringWithFormat:@"SELECT City_Name, City_Picture, City_Id FROM CITIES, COUNTRIES WHERE CITIES.Country_Id=COUNTRIES.Country_Id AND COUNTRIES.Country_Id = '%@'", self.countryID];

    const char *sqlStatement = [querySQL UTF8String];
    sqlite3_stmt *compiledStatement;

    // Init the countries Array
    self.cities = [[NSMutableArray alloc] init];

    // Open the database from the users filessytem
    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
        NSLog(@"success");

        if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
            NSLog(@"success");
            while(sqlite3_step(compiledStatement) == SQLITE_ROW)
            {
                NSLog(@"success");
                // Read the data from the result row
                char *temp_cName = (char *)sqlite3_column_text(compiledStatement, 0);
                NSString *cName = temp_cName == NULL ? nil : [[NSString alloc] initWithUTF8String:temp_cName];

                char *temp_cPicture = (char *)sqlite3_column_text(compiledStatement, 1);
                NSString *cPicture = temp_cPicture == NULL ? nil : [[NSString alloc] initWithUTF8String:temp_cPicture];

                char *temp_cId = (char *)sqlite3_column_text(compiledStatement, 2);
                NSString *cId = temp_cId == NULL ? nil : [[NSString alloc] initWithUTF8String:temp_cPicture];

                NSMutableDictionary *city = [[NSMutableDictionary alloc] init];
                [city setObject:cName forKey:@"City_Name"];
                [city setObject:cPicture forKey:@"City_Picture"];
                [city setObject:cId forKey:@"City_Id"];

                [self.cities addObject:city];
            }
        }
        // Release the compiled statement from memory
        sqlite3_finalize(compiledStatement);   
    }
    sqlite3_close(database);
}

现在我得到了城市列表。当我选择一个城市时，我看不到城市信息。这是第二次实现。

- (void) readCityInfoFromDatabase:(NSString *)querySQL
{
    databaseName = @"123.sqlite";

    NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDir = [documentPaths objectAtIndex:0];
    databasePath = [documentsDir stringByAppendingPathComponent:databaseName];

    // Setup the database object
    sqlite3 *database;

    // Setup the SQL Statement and compile it for faster access

    const char *sqlStatement = [querySQL UTF8String];
    sqlite3_stmt *compiledStatement;

    // Open the database from the users filessytem
    if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {
        NSLog(@"success");
        if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {
            NSLog(@"success");
            if (sqlite3_step(compiledStatement) == SQLITE_ROW)
            {
                NSLog(@"success");

                char *temp_content = (char *)sqlite3_column_text(compiledStatement, 0);
                [self.cityTextView setText:temp_content == NULL ? nil : [[NSString alloc] initWithUTF8String:temp_content]];
            }
        }
        sqlite3_finalize(compiledStatement);
    }
    sqlite3_close(database);
}

前两步是成功的，但是，

    if (sqlite3_step(compiledStatement) == SQLITE_ROW)
    {
        NSLog(@"success");

我看不到这一步成功。

请帮忙。

Answer 1

你真的应该保存 sqlite3_step() 的结果并检查它是否:

• SQLITE_ROW = 检索到的数据行
• SQLITE_DONE = 没有(更多)数据要检索
• 其他 = 发生了一些错误

不过，根据您分享的内容，您很可能只是收到了 SQLITE_DONE，因为没有找到任何东西。如果 SQL 中有错误(例如错误的连接、不正确的 WHERE 子句等)，您可能会得到它。如果没有看到 readCityInfoFromDatabase 使用的 SQL 和数据库中的一些代表性数据，很难说。

顺便说一句，不仅对于 sqlite3_step()，而且对于所有的 sqlite3_xxx() 调用，如果您收到错误，您应该记录 sqlite3_errmsg()。现在，如果出现错误，您必须猜测问题的根源是什么。