如何从SQLite表中检索结果并将其分配给Objective-C中的变量？

Question

我试图从SQlite表中检索结果，然后将它们分配给Objective-C中的变量。我这样做的方法如下：

- (void) readRestaurantsFromDatabase {

//Setup the database object
sqlite3 *database;

//Init the restaurant array
restaurants = [[NSMutableArray alloc] init];

//Open the database from the users filesystem
if (sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) {

    //setup the SQL statement and compile it for faster access
    const char *sqlStatement = "select * from restaurant";
    sqlite3_stmt *compiledStatement;

    if (sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {

        //loop through the results and add them to the feeds array
        while (sqlite3_step(compiledStatement) == SQLITE_ROW) {

            //read the data from the result row
            NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 1)];
            NSString *aAddress = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 2)];
            NSString *aCity = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 3)];
            NSString *aProvinceState = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 4)];
            NSString *aPostalZipCode = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 5)];
            NSString *aCountry = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 6)];
            NSString *aPhoneNumber = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 7)];
            NSString *aHours = [NSString stringWithUTF8String:(char *)sqlite_coluumn_text(compiledStatement, 8)];
            //double aLat
            //double aLon

            Restaurant *restaurant = [[Restaurant alloc] initWithName:aName address:aAddress city:aCity provinceState:aProvinceState postalZipCode:aPostalZipCode country:aCountry phoneNumber:aPhoneNumber hours:aHours latitude:aLat longitude:aLon];

            //add the restaurant object to the restaurant array
            [restaurants addObject:restaurant];

            [restaurant release];

        }


    }

    sqlite3_finalize(compiledStatement);

}

sqlite3_close(database);

}

从sqlite表中检索字符串时没有问题。我的困惑是如何从SQLite表中检索存储为双精度的纬度和经度变量？我如何将这些值分配给变量double aLat，并在上面的代码中加倍aLon？

Answer 1

使用sqlite_column_double。就那么简单：

double aLon = sqlite_column_double(compiledStatement, 9);
double aLat = sqlite_column_double(compiledStatement, 10);

Answer 2

我能想到的最简单的方法是使用float创建一个NSNumber并从中获取double值：

NSNumber *number = [NSNumber numberWithFloat:aFloat];
double aDouble = [number doubleValue];

Answer 3

正如你在其他领域所做的那样。您可以检索它并将双值作为字符串。我还建议你创建一本字典。您可以将所有数据存储在字典中。然后，您可以在Objective C代码中访问它。