Coredata entity calculation approach

Ive gained a lot previously here posting questions about core data. A lot of things cleared. Since my object model has potential uncertainties, i run into a lot of challenges and end up questioning the whole approach.

Oh well, heres the problem. Im gonna write a little more detail than required to explain this,

I have 2 entities:

Code:

Parent Object <-->> Entry object. Parent has a to-many relationship with Entry Object.
Parent 1:
 Name: Height
 Tag: Ht
 
Parent 2:
 Name: Weight
 Tag: Wt

Parent 3:
 Name: Body Mass Index
 Tag: BMI


Entry Object:{
  NSNumber: Value
  NSDate: timeStamp
  ForParent: -->Parent Object

These objects are listed in a tableView. And theres an "Add" button in the navigationItem.

User selects an parent in the list, and taps "Add", a modelView appears and the user inputs the Value and an EntryObject is created for that Parent.
Example, i select Height then tap "Add" and enter the height, and the app records the date added. The date could be manually switched.

Same procedure for "Weight" Parent.

Now If BMI is selected, the modalView shows two textfields, one for height and one for Weight. After the values are entered, an NSNumber is returned by calculating the BMI = [Wt/(Ht*Ht)]. The difference here is that NO Entry Object is created with this value, and simply the number is returned.

Up until now, things work just fine and as desired.

If I fetch Entries (object) of each Parent Object, I'd get:

Code:

Parent-Height = {  Entry(178cm, 10thApril,
                          Entry(187cm, 24thApril,
                       }

Parent-Weight = { Entry(167lbs, 24thApril,
                        }

Parent-BMI = { NO Entry Objects } Instead it pulls in the EntryObjects of height and Weight and parses it and presents the array at runtime. The way i do that is actually create a dictionary with keys as timeStamp (date of entry) and their objects as the entries taken at that timeStamp.

Code:

The dictionary is { 10thApril { 
                                           Height=1.78
                                        }
                          24thApril {
                                           Height=1.87
                                           Weight=167lbs
                                       }
                        }

After parsing, the only nsnumber returned is for the 24thApril as both values are present.

Code:

So the resultant Array becomes: {  167/(1.87*1.87), 24thApril }

I wanted to develop it so that even if "ONE" parent of BMI is missing, in this case, Weight was missing on 10thApril, i'd pull the Weight entry from another date and calculate BMI.
The idea is to step back in time and grab the nearest Weight entry and present that.

Why am i doing so you ask? why not just say hey, no weight entered on 10th hence no BMI then... well, thats cuz
1- some leniency can be granted in health matters, BMI doesn't change suddenly.
2- I wouldn't want to show "N/A", that would just be not fair.. to the user to always enter


This would not apply in every case, but I'm concerned about bmi only.

Any advise on structuring the model or something that makes this more efficient would be great.
I'd really like advice to show BMI in the desired way would be great.

Im Fetching all entries for bmi by creating a NSPredicate and a SortDiscriptor.

Code:

Sorting is via the timeStamp.
Predicate =  "self.ForParent IN parentArray", [NSArray of HeightParent, WeightParent].

And SO i'd get the entries in a sorted like this:

Code:

Entries: { 
              EntryWeight - 24April,  ***
              EntryHeight - 24April,   ---
              EntryHeight - 10April,   ---
              EntryWeight - 1stApril,  *** 
              EntryHeight -  1stApril,  ---
              EntryWeight - 20March, ***
             }

equal number of entries: of height and weight, BUT some dates may have single entries and since i sort with dates first into a dict, i comes like this:

Code:

       Key-24April:      [Array= Wt, Ht]
           key 10APRIL:     [Array= Ht      ]
           Key 1stApril:      [Array = Wt, Ht]
           Key 20March:     [Array= Wt     ]

When I build and parse the BMI,
For example when I get 10April Object: i have ONly Ht in it, i would like to get the next /nearest Weight Object to return a non NIL value.

Ive taken a lot of space to write in detail, and granted, most of you got the point repeatedly, but this is just so critical to the app I'm working on...

 

Hey thanks for the reply,

You've got valid points and my height hasn't changed since about a decade i think , In which case, i have a variable in the Parent that says if its fixed or not.
The reason being:
- If the user is a kid, or someone's checkin their kid's bmi, Height is actually a good index in growth chart.

- When the height is static, i don't even check Entry, i jus grab it from else where, in the Parent object. Theres no point in creating entries for something thats static and going to remain unchanged for good. THe benefit of not creating new entries for statics is simply less results in fetching, less data saving (even if its bytes, should be beneficial in the long term).

Code:

Instead of allowing dates with missing height or weight, create each new timestamp by copying both height and weight from the most recent entry. You now have a new entry with the same height and weight as the prior entry.

I didn't quite get what your saying, all dates that have either height or weight or both are already stored as keys in a dict each (as described in my above post) object is an array of those entries.
When you say create a new timeStamp, since that is attached to an Entry, I'm assuming your saying create a new EntryObject.
The whole point was to get the missing height and weight and 'calculate' the BMI, i don't prefer storing an entry for BMI itself, its parsed at runtime, i see you asking why?

• Potentially i can calculate add an entry object, but incase a user decides to Change the weight for that specific date, (the ability of which i chose to give), i'd have to recalculate the BMI for that Entry of that date.
• If i simply add Height (assuming I'm a kid) and not add Weight, (assuming its not changing much, [dont hammer me for this, I'm also working out unlikely scenarios in my stupid unrealistic quest for app smoothness glory], would i have to add an entry in retrospect for BMIs to fill in the gap, cuz weights and heights are added on different dates.
• Why store these values when they could essentially are equations in nature. Im sacrificing the processing power here, probably slowing things down, but this may pile up if you think about it, And i wanted to keep it simple and calculate it at runtime.

I'll expand graphically for a little bit more understand, BMI is a charting equation, and for each date, in the graph, i plot BMI dots for date. And I present a [dictionary allkeys] as X-axis, and and each key should have a height and weight objects and i calculate and present it.
this is the problem, i need to fill in the blanks where it ONE (height or weight) might be missing in a good way..

Any more ideas? or am i totally insane?
EDIT:

Heres how i create the dictionary, how should i do fill in those blanks..

Code:

 + (NSDictionary*)sortFetchedArrayOfEntries:(NSArray *)EntriesArray{
    NSMutableDictionary *dateSortedDict = [NSMutableDictionary new];
    for(EntryObject *EntryObj in EntriesArray){
        NSDate  *entryDate = EntryObj.timeStamp;
        NSMutableArray *array = (NSMutableArray *)[dateSortedDict objectForKey:entryDate];
        if(!array) array = [NSMutableArray new];
        [array addObject:EntryObj];
        [dateSortedDict setObject:array forKey:entryDate];
    }
    return [NSDictionary dictionaryWithDictionary:dateSortedDict];
}

 

Code:

I don't see the big problem with storing multiple values. I don't think the scale of the data is large enough to worry about it. Even an empty value in an entry has a cost in size, so unless you've analyze this down to the exact number of bytes, I think you're doing Premature Optimization.

I should read through that link, I've been playing around core data a lot since the last couple of months.,
Anyway, you've mentioned "Empty Value" of an entry , yes it has a cost, i don't even create that for BMI, BMI exists only as a Parent Object, if i were to "fetch its entries" so to speak, I'm actually fetching Entries for Height and Weight Parent Objects using a predicate, i have else where in the app that tells me that BMI needs Height and Weight object, and does not itself has any entries. (though it potentially could), but for the reasons i've outlined, (in the above posts), i chose to calculate it and simply return as an NSNumber.

Code:

Entry Entity{
   NSNumber value;
   NSDate timestamp;
   forParent  (relationship with Parent e.g., height/weight)
}

Potentially when writing height and weight, What i do is create a new Entry Entity, add the value, timestamp is recorded, and then i add it to the parent in question, height or weight watever,
entry.forParent = ParentHeightObject;
1 entity for all kinds of entries.

For fetching the BMI,

[NSPredicate predicateWithFormat"forParent IN %@", [NSArray of HeightObject, WeightObject]];
Parent <--- to-many--->> Entry. each entry.forParent would point to either height or weight in the above case, at least thats how I'm working this.[/CODE]

My apologies here, i don't conform to any naming conventions and ending up being confused, i just created that function to sort for charting the data, in this case BMI.

again,

Code:

 + (NSDictionary*)sortFetchedArrayOfEntries:(NSArray *)EntriesArray

What Im actually I'm doing is,

Fetching Entry objects for BMI from the store, and as i mentioned above, it fetches Entry Objects for Height and Weight both, and in the fetchRequest I use timeStamp as the sort descriptor.
Now I get a sorted array of Entry Objects based on timestamp.

I use the above method, and create a dict.
NSDictionary *dict=[self sortFetchedArrayOfEntries:[self fetchedEntries]];
//fetchedEntries method gets the array from fetch request. i get it in the form of
Entry 1.4, time=11April //entry.forParent = height
Entry 69 time=11April //entry.forParent = weight
Entry 1.2, time=4April //entry.forParent = height
Entry 1.1, time=9March //entry.forParent = height

Using that method, I'm attempting to create a dictionary that grabs all the dates from all entries adds them as a key. and adds all the Entry objects in an array as its object.

There are times when a user feeds Height and Weight both in a single form. WHich creates 2 entry objects for each with the exact same timestamp. I'd know that both entries are available and theres no need to look for a missing one.
This is what dictionary i make,

Code:

     Key-24April:      [Array= Wt, Ht]
           key 10APRIL:     [Array= Ht      ]
           Key 1stApril:      [Array = Wt, Ht]
           Key 20March:     [Array= Wt     ]

[dict allkeys] is the array for my x-axis, in a way this is my definitive way of saying that a use has entered some kinda data on this date, and i need to show it.

Day1 = [dict allkeys] objectAtIndex:0] ;

For that day i grab the entries
[Array: EntryHeight(1.4), EntryWeight(69)] = [dict objectForKeyay1];

Since i have both, i can godhead and calculate the BMI,

there will be days when theres only Height! and no weight, in which case, What should be my best move forward, assuming both are changing (growing), i just want to grab the nearest - PAST Weight. to fill in the blank.

I think it would also be pretty easy to select a set of tuples (entries) that included at least one non-null weight and height, which would guarantee you'd be able to find a predecessor with weight and height.

I hope its clearer now..

I know little of what your saying . What should that be?

And a little rephrase of my question, where In this whole process, should i
---> INTERRUPT
---> Checking FOr the MIssing Field
---> Identify its Weight
---> Grab the past weight entry
---> Fill it in the missing
---> CONTINUE with the rest.

the thought of looking back while a for(); is going on is making me nauseous.


really appreciate your help man..

 

Oh man, i was posting a reply and missed this part.

Your probably right..this effort was an attempt to simply future uses of this model. And maybe I'm making this whole thing a lot more complex.

In which case, lets say

A user enters ht/wt in the textfields. I store them as 3 entries, one for ht, one for weight and one for BMI (calculated value).

Action: Now i go back and edit the Weight entry value for that date
Desired Result: i would like the change to also be reflected for the BMI for that date.

Action: I delete the Weight entry completely, Should i be leaving the BMI alone? as its already store calculated the value based on the weight before?
Desired Result: Recalculate the BMI based on an earlier date - value.
How would i do that? again,

Contrast this with what I was doing, the "calculation part AND BMI" was not at all based on stored values, it was about fetched Values available at hand and show the output. (Atleast thats what I thought)...


Another reason i forgot to mention was the potential use of iCloud. I thought I'm reducing at least 0.1% of dependency, by not adding calculated entries, which i could otherwise just do at runtime. Since all core data is synced as transaction logs, and the app would absolutely need to show BMI, i thought why sync a BMI entry log when ht and weight are already being propagated.

I guess those were some reasons, but I'd take your advise seriously if you still recommended the safe old way.

 

Hey thanks aloooooooot for your detailed answer

Really put things to perspective, i wish there was some reward points here like stack overflow, i find this forum very helpful always!


cheers