# How to define a command?

1. Open .kdomain file, first define a command-set.

   For example to define a command create lottery, first define a command-set with an appropriate name, using Lottery as the command set name here:

   command-set Lottery { ... }
   

2. Now define the command inside the command-set.

   
   

    

   
   
   
   
   

   command-set Lottery {
   	command create{ 
   		... 
   	}
   }
   

3. Inside the command definition:

   • specify the input (if any),
   • define one or more pre-conditions(if any)
   • specify the output (if any)
   • define one or more post-condition (if any)

   command-set Lottery {
     command create{
         input(lotteryName:String,amount:Int)
         pre{
           condition AmountMustBeGreaterThanZero => `input.amount>0` failing "Amount must be greater than 0"
         }
         output(result:String)
         post{
          condition lotteryCreated => ...
         }
       }
   }
   

4. In order to implement the command logic follow steps listed here.