i know how to generate class diagram in Xcode for iPhone app.
but i am searching for alternate way to represent it, because my app is very much big and it will difficult
Select the "FirstDemo.xcdatamodeld".Goto the "File" select the "print" option save as pdf formate in "ERD diagram".
Any screen issue faced goto the "File" select the "Page Setup"manage the custom sizes.
You can use Omnigraffle to generate UML diagrams directly from Xcode.
Have a look at this SO answer.
Just download OmniGraffle and then go to File->Open->Select your XcodeProject file
and that's it you'll have a class diagram.
You can use StarUML.
A Ruby script created by 'yoshimkd' that scans all swift code from the specified folders and files and automatically generates an entity diagram (similar to a class diagram) which can be viewed in a browser.
Usage: https://martinmitrevski.com/2016/10/12/swift-class-diagrams-and-more/