CI3 to CI4 - hardest transition points?

Personally, the following topics are of interest to me:

• Namespaces practical use in CI4 with examples
  
• Routing and more practical examples  
  
• Working with database - real app with examples queries  
  
• How to use .env in practical examples  
  
• How to use Filters in practical examples  
  
• How to use Events in practical examples 
  
• How to use Honeypot in practical examples 
  
• How to use Migrations in practical examples
  
• How to use and work Cache / DB-cache in practical examples
  
• How to create API in practical examples
  

And ofcourse i am very waiting your book https://leanpub.com/codeigniter4foundations

+1

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(Using CodeIgniter since 1.x)