Method for working with VirtualForms more easily

[paulcsmith]

It is a common pattern when using VirtualForms to yield the form object and one or more additional objects when the form is valid. For example:

class MyForm < Avram::VirtualForm
  virtual some_field : String

  def submit
    validate_required some_field

    if valid?
      # Only yield the user if form is valid
      yield self, @user
    else
      yield self, nil
    end
  end
end

# Used like this
MyForm.submit do |form, user|
  if user
    # Do something
  else 
    # Do something else
  end
end

This can get repetitive and error-prone.

Another real-life example is here:
https://github.com/luckyframework/lucky_cli/pull/312/files#diff-b6e4ba970ba3c90d012a7fded94d57b2

Proposed solution

From comment here: #69 (comment)

class SearchUsers < Avram::VirtualOperation
  attribute query : String
  step { validate_size query, min: 2 }
  
  def result
    if valid? # If no validation errors on attributes
      UserQuery.search(query.value)
    else
      UserQuery.new.none
    end
  end
end

SearchUsers.run(params) do |operation, results|
  # do something
end

An example of the RequestResetPassword operation. Original here (https://github.com/luckyframework/lucky_cli/blob/d78429c8e40f97af20437cb8199de51c4962159f/src/base_authentication_app_skeleton/src/operations/request_password_reset.cr#L1)

class RequestPasswordReset < Avram::VirtualOperation
  # You can modify this in src/operations/mixins/user_from_email.cr
  include UserFromEmail
  step validate_email

  attribute email : String

  def result
    user_from_email
  end

  def validate_email
    validate_required email
    if user_from_email?
      email.add_error "is not in our system"
    end
  end
end

[paulcsmith]

Further ideas: https://gist.github.com/paulcsmith/9eece27711c512751bdac03976b1bc42

class SearchUsers < Avram::VirtualOperation
  attribute query : String
  step { validate_size query, min: 2 }
  
  def result
    if valid? # If no validation errors on attributes
      UserQuery.search(query.value)
    else
      UserQuery.new.none
    end
  end
end

SearchUsers.run(params) do |operation, results|
  # do something
end