Swift 3 to-one to-many relationship. Wanted to understand how relationship works hence created this small code for to-one to-many swift relationship.

Created two entity Account & User

Account has department as an attribute of type string. User has firstName & lastName as attribute of type string.

In Account entity relationship has been set to-Many it means an Account entity can have many users for the department attribute. in short an department can have many users connected to it.

In User entity relationship has been set to-one. it means User can only be connected to an single department of Account entity.

Program is straight forward. 1 First it will setup Account -> department with "IT Head" 2 Next it will create User -> firstName & lastName 3 Lastly it will fetch the data

Fetching is performed in different ways

• get all the users of an specific department from Account Entity
• get all the department from Account Entity
• get an department of an specific user.
• updatedepartmentofanuser

To update the department of an existing user Follow below steps to understand it.

Compile & run it. It will create an record in coredata with

user.firstName = "Nanu"
user.lastName = "Jogi"

Now stop the stimulator.

Next modify

user.firstName = "Vinod"
user.lastName = "Kamath"

Now run again. & next stop the stimulator.

Next modify

  let dept = "IT Head" // inside the func mysetup() 
  to
  
  let dept = "Purchase"

Next modify

user.firstName = "Manoj"
user.lastName = "Shah"

Now run again. You'll see something like this below

retrieveing all users from account department which belongs to 'it'
User = Vinod Kamath
User = Nanu Jogi

retrieveing all department from Account entity
IT Head
Purchase

we get the department of an specific user
User = IT Head

Now what I wanted was to change the department of "Nanu" from IT Head to Purchase but was just not able to do it.

So settled as of now with deleteing it and then recreating it with department "Purchase".

So see this you need to do below steps. Add comments to mysetup() and createuser() functions. So it will not execute. We don't need them for now.

// Create Account
 //    mysetup() 
 //    createuser()  

next find myfetch() function & uncomment below one line of updatedepartmentofanuser() function.

 updatedepartmentofanuser()

Now run the program & it will first delete the record & then will re-insert it with different department.

To varify it you need to comment the above uncomment line i.e.

// updatedepartmentofanuser() <--- add an comment to this line

RUN it & you'll see that now we only have "Vinod Kamath" as IT Head.

Question:If you know how to update it please enlighten

Cheers