class Ardm::Property
Properties¶ ↑
Properties for a model are not derived from a database structure, but instead explicitly declared inside your model class definitions. These properties then map (or, if using automigrate, generate) fields in your database.
If you are coming to Ardm
from another ORM framework, such as ActiveRecord, this may be a fundamental difference in thinking to you. However, there are several advantages to defining your properties in your models:
-
information about your model is centralized in one place: rather than having to dig out migrations, xml or other configuration files.
-
use of mixins can be applied to model properties: better code reuse
-
having information centralized in your models, encourages you and the developers on your team to take a model-centric view of development.
-
it provides the ability to use Ruby’s access control functions.
-
and, because
Ardm
only cares about properties explicitly defined in your models,Ardm
plays well with legacy databases, and shares databases easily with other applications.
Declaring Properties¶ ↑
Inside your class, you call the property method for each property you want to add. The only two required arguments are the name and type, everything else is optional.
class Post < ActiveRecord::Base property :title, String, :required => true # Cannot be null property :publish, Boolean, :default => false # Default value for new records is false end
By default, Ardm
supports the following primitive (Ruby) types also called core properties:
-
Class
(datastore primitive is the same asString
. Used for Inheritance) -
Object
(marshalled out during serialization) -
String
(default length is 50) -
Text
(limit of 65k characters by default)
Limiting Access¶ ↑
Property
access control is uses the same terminology Ruby does. Properties are public by default, but can also be declared private or protected as needed (via the :accessor option).
class Post < ActiveRecord::Base property :title, String, :accessor => :private # Both reader and writer are private property :body, Text, :accessor => :protected # Both reader and writer are protected end
Access control is also analogous to Ruby attribute readers and writers, and can be declared using :reader and :writer, in addition to :accessor.
class Post < ActiveRecord::Base property :title, String, :writer => :private # Only writer is private property :tags, String, :reader => :protected # Only reader is protected end
Overriding Accessors¶ ↑
The reader/writer for any property can be overridden in the same manner that Ruby attr readers/writers can be. After the property is defined, just add your custom reader or writer:
class Post < ActiveRecord::Base property :title, String def title=(new_title) raise ArgumentError if new_title != 'Lee is l337' super(new_title) end end
Calling super ensures that any validators defined for the property are kept active.
Lazy Loading¶ ↑
By default, some properties are not loaded when an object is fetched in Ardm
. These lazily loaded properties are fetched on demand when their accessor is called for the first time (as it is often unnecessary to instantiate -every- property -every- time an object is loaded). For instance, Ardm::Property::Text
fields are lazy loading by default, although you can over-ride this behavior if you wish:
Example:
class Post < ActiveRecord::Base property :title, String # Loads normally property :body, Text # Is lazily loaded by default end
If you want to over-ride the lazy loading on any field you can set it to a context or false to disable it with the :lazy option. Contexts allow multiple lazy properties to be loaded at one time. If you set :lazy to true, it is placed in the :default context
class Post < ActiveRecord::Base property :title, String # Loads normally property :body, Text, :lazy => false # The default is now over-ridden property :comment, String, :lazy => [ :detailed ] # Loads in the :detailed context property :author, String, :lazy => [ :summary, :detailed ] # Loads in :summary & :detailed context end
Delaying the request for lazy-loaded attributes even applies to objects accessed through associations. In a sense, Ardm
anticipates that you will likely be iterating over objects in associations and rolls all of the load commands for lazy-loaded properties into one request from the database.
Example:
Widget.get(1).components # loads when the post object is pulled from database, by default Widget.get(1).components.first.body # loads the values for the body property on all objects in the # association, rather than just this one. Widget.get(1).components.first.comment # loads both comment and author for all objects in the association # since they are both in the :detailed context
Keys¶ ↑
Properties can be declared as primary or natural keys on a table. You should a property as the primary key of the table:
Examples:
property :id, Serial # auto-incrementing key property :legacy_pk, String, :key => true # 'natural' key
This is roughly equivalent to ActiveRecord’s set_primary_key
, though non-integer data types may be used, thus Ardm
supports natural keys. When a property is declared as a natural key, accessing the object using the indexer syntax Class[key]
remains valid.
User.get(1) # when :id is the primary key on the users table User.get('bill') # when :name is the primary (natural) key on the users table
Indices¶ ↑
You can add indices for your properties by using the :index
option. If you use true
as the option value, the index will be automatically named. If you want to name the index yourself, use a symbol as the value.
property :last_name, String, :index => true property :first_name, String, :index => :name
You can create multi-column composite indices by using the same symbol in all the columns belonging to the index. The columns will appear in the index in the order they are declared.
property :last_name, String, :index => :name property :first_name, String, :index => :name # => index on (last_name, first_name)
If you want to make the indices unique, use :unique_index
instead of :index
Inferred Validations¶ ↑
If you require the dm-validations plugin, auto-validations will automatically be mixed-in in to your model classes: validation rules that are inferred when properties are declared with specific column restrictions.
class Post < ActiveRecord::Base property :title, String, :length => 250, :min => 0, :max => 250 # => infers 'validates_length :title' property :title, String, :required => true # => infers 'validates_present :title' property :email, String, :format => :email_address # => infers 'validates_format :email, :with => :email_address' property :title, String, :length => 255, :required => true # => infers both 'validates_length' as well as 'validates_present' # better: property :title, String, :length => 1..255 end
This functionality is available with the dm-validations gem. For more information about validations, check the documentation for dm-validations.
Default Values¶ ↑
To set a default for a property, use the :default
key. The property will be set to the value associated with that key the first time it is accessed, or when the resource is saved if it hasn’t been set with another value already. This value can be a static value, such as ‘hello’ but it can also be a proc that will be evaluated when the property is read before its value has been set. The property is set to the return of the proc. The proc is passed two values, the resource the property is being set for and the property itself.
property :display_name, String, :default => lambda { |resource, property| resource.login }
Word of warning. Don’t try to read the value of the property you’re setting the default for in the proc. An infinite loop will ensue.
Embedded Values (not implemented yet)¶ ↑
As an alternative to extraneous has_one relationships, consider using an EmbeddedValue.
Property
options reference¶ ↑
:accessor if false, neither reader nor writer methods are created for this property :reader if false, reader method is not created for this property :writer if false, writer method is not created for this property :lazy if true, property value is only loaded when on first read if false, property value is always loaded if a symbol, property value is loaded with other properties in the same group :default default value of this property :allow_nil if true, property may have a nil value on save :key name of the key associated with this property. :field field in the data-store which the property corresponds to :length string field length :format format for autovalidation. Use with dm-validations plugin. :index if true, index is created for the property. If a Symbol, index is named after Symbol value instead of being based on property name. :unique_index true specifies that index on this property should be unique :auto_validation if true, automatic validation is performed on the property :validates validation context. Use together with dm-validations. :unique if true, property column is unique. Properties of type Serial are unique by default. :precision Indicates the number of significant digits. Usually only makes sense for float type properties. Must be >= scale option value. Default is 10. :scale The number of significant digits to the right of the decimal point. Only makes sense for float type properties. Must be > 0. Default is nil for Float type and 10 for BigDecimal
Overriding default Property
options¶ ↑
There is the ability to reconfigure a Property
and it’s subclasses by explicitly setting a value in the Property
, eg:
# set all String properties to have a default length of 255 Ardm::Property::String.length(255) # set all Boolean properties to not allow nil (force true or false) Ardm::Property::Boolean.allow_nil(false) # set all properties to be required by default Ardm::Property.required(true) # turn off auto-validation for all properties by default Ardm::Property.auto_validation(false) # set all mutator methods to be private by default Ardm::Property.writer(:private)
Please note that this has no effect when a subclass has explicitly defined it’s own option. For example, setting the String
length to 255 will not affect the Text
property even though it inherits from String
, because it sets it’s own default length to 65535.
Misc. Notes¶ ↑
-
Properties declared as strings will default to a length of 50, rather than 255 (typical max varchar column size). To overload the default, pass
:length => 255
or:length => 0..255
. SinceArdm
does not introspect for properties, this means that legacy database tables may need theirString
columns defined with a:length
so that DM does not apply an un-needed length validation, or allow overflow. -
You may declare a
Property
with the data-type ofClass
. see SingleTableInheritance for more on how to useClass
columns.
Constants
- INVALID_NAMES
Invalid property names
- Infinity
- JSON
- OPTIONS
- PRIMITIVES
- VISIBILITY_OPTIONS
Possible :visibility option values
Attributes
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
Returns index name if property has index.
@return [Boolean, Symbol
, Array]
returns true if property is indexed by itself returns a Symbol if the property is indexed with other properties returns an Array if the property belongs to multiple indexes returns false if the property does not belong to any indexes
@api public
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
).map { |name| name.to_s }
Returns true if property has unique index. Serial
properties and keys are unique by default.
@return [Boolean, Symbol
, Array]
returns true if property is indexed by itself returns a Symbol if the property is indexed with other properties returns an Array if the property belongs to multiple indexes returns false if the property does not belong to any indexes
@api public
).map { |name| name.to_s }
Public Class Methods
@api public
# File lib/ardm/property.rb, line 427 def accept_options(*args) accepted_options.concat(args) # create methods for each new option args.each do |property_option| class_eval <<-RUBY, __FILE__, __LINE__ + 1 def self.#{property_option}(value = Undefined) # def self.unique(value = Undefined) return @#{property_option} if value.equal?(Undefined) # return @unique if value.equal?(Undefined) descendants.each do |descendant| # descendants.each do |descendant| unless descendant.instance_variable_defined?(:@#{property_option}) # unless descendant.instance_variable_defined?(:@unique) descendant.#{property_option}(value) # descendant.unique(value) end # end end # end @#{property_option} = value # @unique = value end # end RUBY end descendants.each { |descendant| descendant.accepted_options.concat(args) } end
@api public
# File lib/ardm/property.rb, line 422 def accepted_options @accepted_options ||= [] end
# File lib/ardm/property.rb, line 367 def demodulize(name) name.to_s.gsub(/^.*::/,'') end
@api private
# File lib/ardm/property.rb, line 372 def demodulized_names @demodulized_names ||= {} end
@api public
# File lib/ardm/property.rb, line 384 def descendants @descendants ||= DescendantSet.new end
@api semipublic
# File lib/ardm/property.rb, line 362 def determine_class(type) return type if type < Ardm::Property::Object find_class(demodulize(type.name)) end
@api semipublic
# File lib/ardm/property.rb, line 377 def find_class(name) klass = demodulized_names[name] klass ||= const_get(name) if const_defined?(name) klass end
@api private
# File lib/ardm/property.rb, line 389 def inherited(descendant) # Descendants is a tree rooted in Ardm::Property that tracks # inheritance. We pre-calculate each comparison value (demodulized # class name) to achieve a Hash[]-time lookup, rather than walk the # entire descendant tree and calculate names on-demand (expensive, # redundant). # # Since the algorithm relegates property class name lookups to a flat # namespace, we need to ensure properties defined outside of DM don't # override built-ins (Serial, String, etc) by merely defining a property # of a same name. We avoid this by only ever adding to the lookup # table. Given that DM loads its own property classes first, we can # assume that their names are "reserved" when added to the table. # # External property authors who want to provide "replacements" for # builtins (e.g. in a non-DM-supported adapter) should follow the # convention of wrapping those properties in a module, and include'ing # the module on the model class directly. This bypasses the DM-hooked # const_missing lookup that would normally check this table. descendants << descendant Property.demodulized_names[demodulize(descendant.name)] ||= descendant # inherit accepted options descendant.accepted_options.concat(accepted_options) # inherit the option values options.each { |key, value| descendant.send(key, value) } super end
@api semipublic
# File lib/ardm/property.rb, line 765 def initialize(model, name, options = {}) options = options.to_hash.dup if INVALID_NAMES.include?(name.to_s) || (kind_of?(Boolean) && INVALID_NAMES.include?("#{name}?")) raise ArgumentError, "+name+ was #{name.inspect}, which cannot be used as a property name since it collides with an existing method or a query option" end assert_valid_options(options) predefined_options = self.class.options @model = model @name = name.to_s.chomp('?').to_sym @options = predefined_options.merge(options).freeze @instance_variable_name = "@#{@name}".freeze @coercion_method = @options.fetch(:coercion_method) @load_as = self.class.load_as @dump_as = self.class.dump_as @field = @options[:field].freeze unless @options[:field].nil? @default = @options[:default] @serial = @options.fetch(:serial, false) @key = @options.fetch(:key, @serial) @unique = @options.fetch(:unique, @key ? :key : false) @required = @options.fetch(:required, @key) @allow_nil = @options.fetch(:allow_nil, !@required) @allow_blank = @options.fetch(:allow_blank, !@required) @index = @options.fetch(:index, false) @unique_index = @options.fetch(:unique_index, @unique) @lazy = @options.fetch(:lazy, false) && !@key determine_visibility bind end
Gives all the options set on this property
@return [Hash] with all options and their values set on this property
@api public
# File lib/ardm/property.rb, line 453 def options options = {} accepted_options.each do |name| options[name] = send(name) if instance_variable_defined?("@#{name}") end options end
@api deprecated
# File lib/ardm/property.rb, line 462 def primitive(*args) warn "Ardm::Property.primitive is deprecated, use .load_as instead (#{caller.first})" load_as(*args) end
Public Instance Methods
Returns whether or not the property can be a blank value
@return [Boolean]
whether or not the property can be blank
@api public
# File lib/ardm/property.rb, line 578 def allow_blank? @allow_blank end
Returns whether or not the property can accept ‘nil’ as it’s value
@return [Boolean]
whether or not the property can accept 'nil'
@api public
# File lib/ardm/property.rb, line 568 def allow_nil? @allow_nil end
Asserts value is valid
@param [Object] loaded_value
the value to be tested
@return [Boolean]
true if the value is valid
@raise [Property::InvalidValueError]
if value is not valid
# File lib/ardm/property.rb, line 716 def assert_valid_value(value) unless valid?(value) raise Property::InvalidValueError.new(self,value) end true end
A hook to allow properties to extend or modify the model it’s bound to. Implementations are not supposed to modify the state of the property class, and should produce no side-effects on the property instance.
# File lib/ardm/property.rb, line 473 def bind # no op end
Supplies the field in the data-store which the property corresponds to
@return [String] name of field in data-store
@api semipublic
# File lib/ardm/property.rb, line 482 def field # defer setting the field with the adapter specific naming # conventions until after the adapter has been setup @field ||= model.field_naming_convention.call(self).freeze end
Standardized reader method for the property
@param [Resource] resource
model instance for which this property is to be loaded
@return [Object]
the value of this property for the provided instance
@raise [ArgumentError] “resource
should be a Resource, but was .…”
@api private
# File lib/ardm/property.rb, line 593 def get(resource) get!(resource) end
Fetch the ivar value in the resource
@param [Resource] resource
model instance for which this property is to be unsafely loaded
@return [Object]
current @ivar value of this property in +resource+
@api private
# File lib/ardm/property.rb, line 606 def get!(resource) #resource.instance_variable_get(instance_variable_name) val = resource.send :read_attribute, field if val.nil? set_default_value(resource) else val end end
Returns a concise string representation of the property instance.
@return [String]
Concise string representation of the property instance.
@api public
# File lib/ardm/property.rb, line 729 def inspect "#<#{self.class.name} @model=#{model.inspect} @name=#{name.inspect}>" end
Returns whether or not the property is a key or a part of a key
@return [Boolean]
true if the property is a key or a part of a key
@api public
# File lib/ardm/property.rb, line 538 def key? @key end
Returns whether or not the property is to be lazy-loaded
@return [Boolean]
true if the property is to be lazy-loaded
@api public
# File lib/ardm/property.rb, line 528 def lazy? @lazy end
Check if the attribute corresponding to the property is loaded
@param [Resource] resource
model instance for which the attribute is to be tested
@return [Boolean]
true if the attribute is loaded in the resource
@api private
# File lib/ardm/property.rb, line 664 def loaded?(resource) resource.send(:read_attribute, field) != nil #resource.instance_variable_defined?(instance_variable_name) #true end
# File lib/ardm/property.rb, line 747 def primitive warn "#primitive is deprecated, use #dump_as instead (#{caller.first})" dump_as end
Test a value to see if it matches the primitive type
@param [Object] value
value to test
@return [Boolean]
true if the value is the correct type
@api semipublic
# File lib/ardm/property.rb, line 742 def primitive?(value) warn "#primitive? is deprecated, use #value_dumped? instead (#{caller.first})" value_dumped?(value) end
@api private
# File lib/ardm/property.rb, line 671 def properties @properties ||= model.properties end
Returns whether or not the property must be non-nil and non-blank
@return [Boolean]
whether or not the property is required
@api public
# File lib/ardm/property.rb, line 558 def required? @required end
Returns whether or not the property is “serial” (auto-incrementing)
@return [Boolean]
whether or not the property is "serial"
@api public
# File lib/ardm/property.rb, line 548 def serial? @serial end
Provides a standardized setter method for the property
@param [Resource] resource
the resource to get the value from
@param [Object] value
the value to set in the resource
@return [Object]
+value+ after being typecasted according to this property's primitive
@raise [ArgumentError] “resource
should be a Resource, but was .…”
@api private
# File lib/ardm/property.rb, line 634 def set(resource, value) set!(resource, typecast(value)) end
Set the ivar value in the resource
@param [Resource] resource
the resource to set
@param [Object] value
the value to set in the resource
@return [Object]
the value set in the resource
@api private
# File lib/ardm/property.rb, line 649 def set!(resource, value) #resource.instance_variable_set(instance_variable_name, value) resource.send :write_attribute, field, value resource.send :read_attribute, field end
# File lib/ardm/property.rb, line 616 def set_default_value(resource) return if loaded?(resource) || !default? set(resource, default_for(resource)) end
@api semipublic
# File lib/ardm/property.rb, line 676 def typecast(value) @coercer ||= Coercible::Coercer.new if Array === value value.map { |v| typecast(v) } else @coercer[value.class].send(coercion_method, value) end rescue Coercible::UnsupportedCoercion value end
Returns true if property is unique. Serial
properties and keys are unique by default.
@return [Boolean]
true if property has uniq index defined, false otherwise
@api public
# File lib/ardm/property.rb, line 495 def unique? !!@unique end
Test the value to see if it is a valid value for this Property
@param [Object] loaded_value
the value to be tested
@return [Boolean]
true if the value is valid
@api semipulic
# File lib/ardm/property.rb, line 696 def valid?(value, negated = false) dumped_value = dump(value) if required? && dumped_value.nil? negated || false else value_dumped?(dumped_value) || (dumped_value.nil? && (allow_nil? || negated)) end end
@api semipublic
# File lib/ardm/property.rb, line 753 def value_dumped?(value) value.kind_of?(dump_as) end
@api semipublic
# File lib/ardm/property.rb, line 758 def value_loaded?(value) value.kind_of?(load_as) end
Protected Instance Methods
@api private
# File lib/ardm/property.rb, line 805 def assert_valid_options(options) keys = options.keys if (unknown_keys = keys - self.class.accepted_options).any? raise ArgumentError, "options #{unknown_keys.map { |key| key.inspect }.join(' and ')} are unknown" end options.each do |key, value| boolean_value = value == true || value == false case key when :field assert_kind_of "options[:#{key}]", value, ::String when :default if value.nil? raise ArgumentError, "options[:#{key}] must not be nil" end when :serial, :key, :allow_nil, :allow_blank, :required, :auto_validation unless boolean_value raise ArgumentError, "options[:#{key}] must be either true or false" end if key == :required && (keys.include?(:allow_nil) || keys.include?(:allow_blank)) raise ArgumentError, 'options[:required] cannot be mixed with :allow_nil or :allow_blank' end when :index, :unique_index, :unique, :lazy unless boolean_value || value.kind_of?(Symbol) || (value.kind_of?(Array) && value.any? && value.all? { |val| val.kind_of?(Symbol) }) raise ArgumentError, "options[:#{key}] must be either true, false, a Symbol or an Array of Symbols" end when :length assert_kind_of "options[:#{key}]", value, Range, ::Integer when :size, :precision, :scale assert_kind_of "options[:#{key}]", value, ::Integer when :reader, :writer, :accessor assert_kind_of "options[:#{key}]", value, Symbol unless VISIBILITY_OPTIONS.include?(value) raise ArgumentError, "options[:#{key}] must be #{VISIBILITY_OPTIONS.join(' or ')}" end end end end
Assert given visibility value is supported.
Will raise ArgumentError if this Property’s reader and writer visibilities are not included in VISIBILITY_OPTIONS
.
@return [undefined]
@raise [ArgumentError] “property visibility must be :public, :protected, or :private”
@api private
# File lib/ardm/property.rb, line 864 def determine_visibility default_accessor = @options.fetch(:accessor, :public) @reader_visibility = @options.fetch(:reader, default_accessor) @writer_visibility = @options.fetch(:writer, default_accessor) end