Question

I read some articles and info in developer.apple.com about Core Data. Now I want to create ManagedObjectModel for my app. So I need to help – because it’s first my planning about database. So my app will have next options

1. User must login with his Login and Password. So if he forget password, there is chance to create new pass by entering correct answer on secret question.
2. App will store contacts. Every contact have name, surname, photo, phones, and coollection of map annotations.
3. User can create some groups (like Family, Friends…)

So this app I create for understanding basics of objective-c and maybe there are no logic in my app.
Please check my entities, maybe I allowed blunder.

First entity Contact

• id – number of contact.
• image – I will store array there. So if image <200 Kb I insert it in database, if more I will save the path to this image
• map – the dictionary of map annotations
• name
• phones – array of phone numbers
• surname

Second entity Group

• contacts – array that contain id of contacts, that belong to this group
• id – number of group
• title – it is the name of group (like Family, Friends…)

Third entity Login

• groups – array that contain id of groups, that belong to this group
• login
• password
• secret answer – answer to the secret question
• secret question

Relationships

So each Login can have some groups, but each group will belong only to one Login. So I create “to-many relationship” for group relationship. So each group contain some contacts and contacts can be in some different gruops – I create many-to-many relationship.

About property “optional”. I understand that if it’s not check – this attribute or relationship have to be. So I remove this property for

• “id” in Contact
• “id” in Group
• “login”, “password” in Login
• in relationship “toGroups” in Contact
• in relationship “toLogin” in Group

About “Delete Rule”. I want if I delete some Login all groups and contacts belong to this login must be delete. I can choose “Cascade” for relationship “group” in Login but it will delete only groups but not contacts. I cann’t do such for relationship “toContact” because if I delete some Group it will delete contacts, but other Groups still can have this contacts. So maybe I must create attribute “contact” in Login that will be array of contacts, and create relationship to Contacts and if I delete Login all groups and contacts that belong to it, will be delete.

PS Sorry I am stil newbie and my question maybe funny for you, but I need help

Answer 1

A few things I noticed –

1. You have no need to use ‘id’ properties. Most databases plan on these for primary/foreign key management, but core data will manage this all for you provided you have the relationships set up. Also by this logic, you don’t need properties to manually create that relationship (i.e. ‘Contacts’ in group and ‘groups’ in login
2. Are you sure you wants to be storing dictionaries and/or arrays in an entity? These sound like another standalone entity such as one for map annotations. Then you would build a one-to-many relationship from the original object to the new one.
3. Images stored as binary data are not the most efficient way to go about this. Its better to use the filesystem the app sandbox provides. Just saw a similar question the other day Storing images locally on an iOS device