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 assumme 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