Reading from SQL database into NSArray

Question

I have an iPad that reads data from an SQL database. The following code works fine and retrieves 2 fields from each record and reads them into an NSArray.

I now need to read 5 of the fields and I can't help but think that there is a better way of doing it rather than running 5 separate queries through php (the getinfo.php file with the choice parameter set to pick the different fields).

Any pointers to a better method for doing this?

NSString *strURLClass = [NSString stringWithFormat:@"%@%@", @"http://wwwaddress/getinfo.php?choice=1&schoolname=",obsSchoolName];
NSArray *observationsArrayClass = [[NSMutableArray alloc] initWithContentsOfURL:[NSURL URLWithString:strURLClass]];
observationListFromSQL = [[NSMutableArray alloc]init];
NSEnumerator *enumForObsClass = [observationsArrayClass objectEnumerator];

NSString *strURLDate = [NSString stringWithFormat:@"%@%@", @"http://wwwaddress/getinfo.php?choice=5&schoolname=",obsSchoolName];
NSArray *observationsArrayDate = [[NSMutableArray alloc] initWithContentsOfURL:[NSURL URLWithString:strURLDate]];
observationListFromSQL = [[NSMutableArray alloc]init];
NSEnumerator *enumForObsDate = [observationsArrayDate objectEnumerator];

id className, dateOfObs;

while (className = [enumForObsClass nextObject])
{
    dateOfObs = [enumForObsDate nextObject];
    [observationListFromSQL addObject:[NSDictionary dictionaryWithObjectsAndKeys:className, @"obsClass", dateOfObs, @"obsDate",nil]];
}

Sergey Kalinichenko · Accepted Answer · 2013-07-28 11:17:58Z

1

Yes, you can do that with less code by "folding" the statements into a loop, and using a mutable dictionary:

// Add other items that you wish to retrieve to the two arrays below:
NSArray *keys = @[@"obsClass", @"obsDate"]; // Key in the dictionary
NSArray *choices = @[@1, @5];               // Choice in the URL string
NSMutableArray *res = [NSMutableArray array];
NSMutableArray *observationListFromSQL = [NSMutableArray array];
for (int i = 0 ; i != keys.count ; i++) {
    NSNumber *choice = choices[i];
    NSString *strURLClass = [NSString stringWithFormat:@"http://wwwaddress/getinfo.php?choice=%@&schoolname=%@", choice, obsSchoolName];
    NSArray *observationsArray = [[NSMutableArray alloc] initWithContentsOfURL:[NSURL URLWithString:strURLClass]];
    NSEnumerator *objEnum = [observationsArrayClass objectEnumerator];
    NSString *key = keys[i];
    NSMutableDictionary *dict;
    if (res.count < i) {
        dict = res[i];
    } else {
        dict = [NSMutableDictionary dictionary];
        [res addObject:dict];
    }
    id item;
    while (item = [objEnum nextObject]) {
        [res setObject:item forKey:key];
    }
}

edited Jul 28, 2013 at 11:17

answered Jul 28, 2013 at 10:49

Sergey Kalinichenko

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4 Comments

RGriffiths Over a year ago

Thank you. That is neat and means less code, but it still runs the php query 5 times if I want 5 fields. Can the data not be passed back from a single call of the php file?

Sergey Kalinichenko Over a year ago

@RichardGriffiths That depends on the service that supplies the data: if it provides you a way to supply several choices in a single call, and defines a way for you to decode the data coming back, then the answer is "yes". Also, if there is a way to not provide any choices, get back all fields, and then choose the five fields, that you want, you might save on round-trips at the expense of receiving more data (usually a very beneficial tradeoff). Otherwise, you would need to perform multiple calls.

RGriffiths Over a year ago

Brillant. Really helpful thanks. Trying your code and I get the error on dict = res[i]; and res[i] = dict; "Expected method to read array element not found on object of type 'NSMutableDictionary *". Also should the line NSEnumerator *objEnum = [observationsArrayClass objectEnumerator]; be just 'observationsArray'?

Sergey Kalinichenko Over a year ago

@RichardGriffiths That was supposed to be an array - I fixed that, and also put addObject in the else branch.

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