ModelLifecycle

Some useful functionalities are present in each model:

persisted?

The persisted? method allows you to test if a model has been saved in the database or not:

m = MyModel.new
m.persisted? #false
m.save!
m.persisted? #true
m.delete
m.persisted? #false

readonly?

Model can be flagged as readonly. They will trigger an error on update/save:

class MyModel
  include Clear::Model
  #...
  def readonly?
    true
  end
end

columns

For each column defined, a second property [column_name]_column is created. This allow you to check the current status of the column:

class MyModel
  column name : String 
end

m = MyModel.new({name: "test"})
m.name_column.defined? #Return true, because defined in the construction.
m.save!
m.name_column.changed? #return false
m.changed? #false
m.name = "test2"
m.changed? #true
m.name_column.changed? #return true
m.name_column.old_value #return "test"
m.name_column.revert #return to "test"
m.changed? #false

function
defined?	Check if the value has been defined at least once. Note than nil in case of nullable column can is a defined value !
changed?	Check if the column has been changed since last save
old_value	Return the old value of the column, or UNDEFINED if not changed
revert	Revert the column to old value. If no old value, return the column into UNDEFINED state
nilable?	Check whether the column can be nil
value	Try to get the value of the column. If the column is UNDEFINED, throw an exception.
value(default)	Try to get the value of the column. If the column is UNDEFINED, return default
clear	Set the column as UNDEFINED
dirty!	Flag the column as dirty (has been changed)
clear_change_flag	Inverse of dirty, tell Clear the column didn't changed
failed_to_be_present?	Return true if the column must be present and is not.

to_h and to_update_h

Crystal offers two methods to access to the current fields of the model:

• to_h return a hash version of the columns of the model
• to_update_h return a curated hash version of only the changed columns of the model