UR::Object::Property(3pm)

NAME
UR::Object::Property - Class representing metadata about a class property

SYNOPSIS
  my $prop = UR::Object::Property->get(class_name => 'Some::Class', property_name => 'foo');

  my $class_meta = Some::Class->__meta__;
  my $prop2 = $class_meta->property_meta_for_name('foo');

  # Print out the meta-property name and its value of $prop2
  print map { " $_ : ".$prop2->$_ }
        qw(class_name property_name data_type default_value);

DESCRIPTION
Instances of this class represent properties of classes. For every item mentioned in the 'has' or 'id_by' section of a class definition become Property objects.

INHERITANCE
UR::Object::Property is a subclass of UR::Object

PROPERTY TYPES
For this class definition:
  class Some::Class {
      has => [
          other_id => { is => 'Text' },
          other => { is => 'Some::Other', id_by => 'foo_id' },
          bar => { via => 'other', to => 'bar' },
          foos => { is => 'Some::Foo', reverse_as => 'some', is_many => 1 },
          uc_other_id => { calculate_from => 'other_id',
                        calculate_perl => 'uc($other_id)' },
      ],
  };

Properties generally fall in to one of these categories:

regular property
    A regular property of a class holds a single scalar. In this case, 'other_id' is a regular property.

object accessor
    An object accessor property returns objects of some class. The properties of this class must link in some way with all the ID properties of the remote class (the 'is' declaration). 'other' is an object accessor property. This is how one-to-one relationships are implemented.

via property
    When a class has some object accessor property, and it is helpful for an object to assume the value of the remote class's properties, you can set up a 'via' property. In the example above, an object of this class gets the value of its 'bar' property via the 'other' object it's linked to, from that object's 'bar' property.

reverse as or is many property
    This is how one-to-many relationships are implemented. In this case, the Some::Foo class must have an object accessor property called 'some', and the 'foos' property will return a list of all the Some::Foo objects where their 'some' property would have returned that object.

calculated property
    A calculated property doesn't store its data directly in the object, but when its accessor is called, the calculation code is executed.

PROPERTIES
Each property has a method of the same name

  Direct Properties

class_name => Text
    The name of the class this Property is attached to

property_name => Text
    The name of the property. The pair of class_name and property name are the ID properties of UR::Object::Property

column_name => Text
    If the class is backed by a database table, then the column this property's data comes from is stored here

data_type => Text
    The type of data stored in this property. Corresponds to the 'is' part of a class's property definition.

data_length => Number
    The maximum size of data stored in this property

default_value
    For is_optional properties, the default value given when an object is created and this property is not assigned a value.

valid_values => ARRAY
    A listref of enumerated values this property may be set to

doc => Text
    A place for documentation about this property

is_id => Boolean
    Indicates whether this is an ID property of the class

is_optional => Boolean
    Indicates whether this is property may have the value undef when the object is created

is_transient => Boolean
    Indicates whether this is property is transient?

is_constant => Boolean
    Indicates whether this property can be changed after the object is created.

is_mutable => Boolean
    Indicates this property can be changed via its accessor. Properties cannot be both constant and mutable

is_volatile => Boolean
    Indicates this property can be changed by a mechanism other than its normal accessor method. Signals are not emitted even when it does change via its normal accessor method.

is_classwide => Boolean
    Indicates this property's storage is shared among all instances of the class. When the value is changed for one instance, that change is effective for all instances.

is_delegated => Boolean
    Indicates that the value for this property is not stored in the object directly, but is delegated to another object or class.

is_calculated => Boolean
    Indicates that the value for this property is not a part of the object'd data directly, but is calculated in some way.

is_transactional => Boolean
    Indicates the changes to the value of this property is tracked by a Context's transaction and can be rolled back if necessary.

is_abstract => Boolean
    Indicates this property exists in a base class, but must be overridden in a derived class.

is_concrete => Boolean
    Antonym for is_abstract. Properties cannot be both is_abstract and is_concrete,

is_final => Boolean
    Indicates this property cannot be overridden in a derived class.

is_deprecated => Boolean
    Indicates this property's use is deprecated. It has no effect in the use of the property in any way, but is useful in documentation.

implied_by => Text
    If this property is created as a result of another property's existence, implied_by is the name of that other property. This can happen in the case where an object accessor property is defined

      has => [
          foo => { is => 'Some::Other', id_by => 'foo_id' },
      ],

    Here, the 'foo' property requires another property called 'foo_id', which is not explicitly declared. In this case, the Property named foo_id will have its implied_by set to 'foo'.

id_by => ARRAY
    In the case of an object accessor property, this is the list of properties in this class that link to the ID properties in the remote class.

reverse_as => Text
    Defines the linking property name in the remote class in the case of an is_many relationship

via => Text
    For a via-type property, indicates which object accessor to go through.

to => Text
    For a via-type property, indicates the property name in the remote class to get its value from. The default value is the same as property_name

where => ARRAY
    Supplies additional filters for indirect properties. For example:

      foos => { is => 'Some::Foo', reverse_as => 'some', is_many => 1 },
      blue_foos => { via => 'foos', where => [ color => 'blue' ] },

    Would create a property 'blue_foos' which returns only the related Some::Foo objects that have 'blue' color.

calculate_from => ARRAY
    For calculated properties, this is a list of other property names the calculation is based on

calculate_perl => Text
    For calculated properties, a string containing Perl code. Any properties mentioned in calculate_from will exist in the code's scope at run time as scalars of the same name.

class_meta => UR::Object::Type
    Returns the class metaobject of the class this property belongs to

METHODS

via_property_meta
    For via/to delegated properties, return the property meta in the same class this property delegates through

to_property_meta
    For via/to delegated properties, return the property meta on the foreign class that this property delegates to

SEE ALSO
UR::Object::Type, UR::Object::Type::Initializer, UR::Object