macOS Need help with a conversion from SQLite data to Class Object

[Anim]

Hey all

I am pulling my hair out trying to work out how to convert a category list into a data model for a NSOutlineView.

I am attempting to create a Source view / NSOutlineView to let a user select a product category. Just like a tree view. There are no Leaf nodes, just roots and branches.

The user entered data is stored in an SQLite table as the following:

ID           PRODUCT         PARENTID
1            FORD            0
2            HONDA           0
3            FIESTA          1
4            XR2             3
5            ESCORT          1
6            CIVIC           2
7            TURBO           6

Three could be 20 or 1000 of these records, the user is allowed to add and delete them.

So we can see there are 2 root nodes (Ford, Honda) and various branches and branches of branches (Turbo, XR2)

So, for the data model I created a class to hold the data as in:

#import <Foundation/Foundation.h>

@interface BP_category : NSObject

@property (copy) NSString *categoryName;
@property (readonly, copy) NSMutableArray *subCategory;

-(id)initWithName:(NSString *)name;
-(void)addChildCategory:(BP_category *)c;

@end

------------------

#import "BP_category.h"

@implementation BP_category

-(id)init {
    return [self initWithName:@"Untitled"];
}

-(id)initWithName:(NSString *)name {
    self = [super init];
    if (self) {
        _categoryName = [name copy];
        _subCategory  = [[NSMutableArray alloc]init];
    }
    
return self;
}

-(void)addChildCategory:(BP_category *)c {
    [_subCategory addObject:c];
}


@end

What I can't figure out is how to traverse the SQLite data and store it in the class object. I get muddled up when it comes to children of children.

Any help would be much appreciated.

I am also using FMDB as an SQLite wrapper.

Many thanks
Anim

 

[MasConejos]

I can't help you with the cocoa syntax, but I can help from a general programming point of view.

First you will need to add Id as a property of BP_Category

Next you will need to do something like the following. Note that I dont know how sql access works in cocoa, I'm assuming (possible incorrectly) that it is vaguely similar to how .net works

-(NSMutableArray*) getCategoriesFromSql()
{
	//create MySQL connection
	//Create Command object
	//execute SQL query, get a MySqlReader
	
	//This list is a temporary list used for looking up parent categories
	NSMutableArray* listCategories = [[NSMutableArray alloc] init];
	
	//This list is for holding the top level categories
	NSMutableArray* listTopeLevelCategories = [[NSMutableArray alloc] init];
	
	while(reader.read())
	{
		int id = reader["ID"];
		NSString* product = reader["Product"];
		int parentId = reader["ParentID"];
		
		//create object for current record
		BP_category* newCategory = [[BP_Category alloc]initWithName:product withId:id]
		
		//search to see if parent exists
		BP_category* parentCategory = nil;
		foreach(BP_category* category in listCategories)
		{
			if(cat.id == parentId)
			{
				parentCategory = cat;
				break;
			}
		}
		
		//if a parent was found, add the new category as a child
		//otherwise, add it to the top level list
		if(parentCategory)
		{
			[parentCategory addChildCategory:newCategory];
		}
		else
		{
			[listTopeLevelCategories addObject:newCategory];
		}
		
		//add the new category to our lookup list
		[listCategories addObject:newCategory];
	}
	
	return listTopeLevelCategories;
}

 

[Anim]

Interesting, thanks. I will convert that and see how it functions. My issue was when adding a child of a child of a root to the array and where i get confused if there are say 10 child records of a particular root object. I knew I needed a loop within a loop to locate child categories but it was the storing of each parent and accessing a parent (so I can add a child to it) later in the record set.

But, I will take a look at this and see how it works.

Thanks again
Anim

 

[Anim]

Another possible solution I found earlier was to use Cocoa bindings and an NSDictionary object which works well with NSOutlineView's and a NSTreeController for managing it.

As shown here: http://daemonconstruction.blogspot.co.uk/2012/03/simplest-nstreecontroller-example.html

I can then just work with a Dictionary object.

I will try both methods and time them on 1000 records to see which is faster, an array of class objects vs a Dictionary for the data model.

Cheers
Anim

 

[MasConejos]

Mine isn't super optimized. For the lookup list you'd be better off using a dictionary or some other container to look up the categories directly by Id, rather than looping through the entire list trying to find it.

Good luck, either way.

 

[Mac_Max]

When I'm prototyping schemas I'll create wrapper classes around NSDictionaries and convert them into a proper implementation once my schema is set. Maybe it's my C#/Perl background coming out but it also lends itself to emulating C#'s named parameters/Perl object constructors.

I.e.

MyClass *obj = [[MyClass alloc] initWithDictionary:@{
                          @"name"     : someVar1, 
                          @"tag"         : someVar1, 
                          @"location"  : someVar1, 
                          @"time"       : someVar1, 
                       }];

 

[lee1210]

When I'm prototyping schemas I'll create wrapper classes around NSDictionaries and convert them into a proper implementation once my schema is set. Maybe it's my C#/Perl background coming out but it also lends itself to emulating C#'s named parameters/Perl object constructors.

I.e.

MyClass *obj = [[MyClass alloc] initWithDictionary:@{
                          @"name"     : someVar1, 
                          @"tag"         : someVar1, 
                          @"location"  : someVar1, 
                          @"time"       : someVar1, 
                       }];

Erk. I think it was Ben Franklin who said:
"He who would give up compile-time type safety and requiredness for convenience deserves neither."

-Lee

 

[Mac_Max]

Erk. I think it was Ben Franklin who said:
"He who would give up compile-time type safety and requiredness for convenience deserves neither."

-Lee

He also came up with Daylight Savings Time. Not all of his ideas were good in the long run .

The key word there is "prototyping". Having a class to search for is a lot nicer than grepping for "theNameOfSomeRandomDictionaryImKillingMySelfOver".

After I'm done prototyping the class can easily turn into

[[MyClass alloc] initWithName: someVar1
                          tag: someVar2, 
                          location: someVar3];