I want to create an operation which accepts a json array and creates several objects. Something like Books::CreateCollection. 
I believe I need to somehow reuse Books::Create - just call it multiple times and wrap the whole loop in transaction. 
json:
{
 "books": [
    {
       title: "A Tale Of Two Cities"
    },
    {
       title: "Don Quixote"
    }
 ]
}
But how the contract of Books::CreateCollection should look like?
Trailblazer 0.3.0
 
                        
Your contract can handle this.
This is basic Reform wizardry.
The contract will now create one
Bookinstance per incoming hash fragment in thesongsarray.