Class | DataMapper::Property |
In: |
lib/dm-core/adapters/oracle_adapter.rb
lib/dm-core/property.rb |
Parent: | Object |
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 repository/database.
If you are coming to DataMapper 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:
in
your models, DataMapper plays well with legacy databases, and shares databases easily with other applications.
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 include DataMapper::Resource property :title, String, :nullable => false # Cannot be null property :publish, Boolean, :default => false # Default value for new records is false end
By default, DataMapper supports the following primitive (Ruby) types also called core types:
Other types are known as custom types.
For more information about available Types, see DataMapper::Type
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 include DataMapper::Resource 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 include DataMapper::Resource property :title, String, :writer => :private # Only writer is private property :tags, String, :reader => :protected # Only reader is protected end
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 include DataMapper::Resource property :title, String def title=(new_title) raise ArgumentError if new_title != 'Luke is Awesome' @title = new_title end end
By default, some properties are not loaded when an object is fetched in DataMapper. 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, DataMapper::Types::Text fields are lazy loading by default, although you can over-ride this behavior if you wish:
Example:
class Post include DataMapper::Resource 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 multipule lazy properties to be loaded at one time. If you set :lazy to true, it is placed in the :default context
class Post include DataMapper::Resource 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, DataMapper 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
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 DataMapper 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
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
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 include DataMapper::Resource property :title, String, :length => 250 # => infers 'validates_length :title, :minimum => 0, :maximum => 250' property :title, String, :nullable => false # => infers 'validates_present :title property :email, String, :format => :email_address # => infers 'validates_format :email, :with => :email_address property :title, String, :length => 255, :nullable => false # => 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, part of the dm-more bundle. For more information about validations, check the documentation for dm-validations.
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 => { |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.
As an alternative to extraneous has_one relationships, consider using an EmbeddedValue.
: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 :nullable if true, property may have a nil value on save :key name of the key associated with this property. :serial if true, field value is auto incrementing :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 type. All other keys you pass to +property+ method are stored and available as options[:extra_keys].
OPTIONS | = | [ :accessor, :reader, :writer, :lazy, :default, :nullable, :key, :serial, :field, :size, :length, :format, :index, :unique_index, :auto_validation, :validates, :unique, :precision, :scale, :min, :max | NOTE: PLEASE update OPTIONS in DataMapper::Type when updating them here | |
PRIMITIVES | = | [ TrueClass, String, Float, Integer, BigDecimal, DateTime, Date, Time, Object, Class, ].to_set.freeze | ||
VISIBILITY_OPTIONS | = | [ :public, :protected, :private ].to_set.freeze | Possible :visibility option values | |
DEFAULT_LENGTH | = | 50 | ||
DEFAULT_PRECISION | = | 10 | ||
DEFAULT_SCALE_BIGDECIMAL | = | 0 | ||
DEFAULT_SCALE_FLOAT | = | nil | ||
DEFAULT_NUMERIC_MIN | = | 0 | ||
DEFAULT_NUMERIC_MAX | = | 2**31-1 |
default | [R] | |
instance_variable_name | [R] | |
max | [R] | |
min | [R] | |
model | [R] | |
name | [R] | |
options | [R] | |
precision | [R] | |
primitive | [R] | |
reader_visibility | [R] | |
repository_name | [R] | |
scale | [R] | |
type | [R] | |
writer_visibility | [R] |
Returns whether or not the property is custom (not provided by dm-core)
@return [Boolean]
whether or not the property is custom
@api public
Returns true if the property has a default value
@return [Boolean]
true if the property has a default value
@api semipublic
Returns a default value of the property for given resource.
When default value is a callable object, it is called with resource and property passed as arguments.
@param [Resource] resource
the model instance for which the default is to be set
@return [Object]
the default value of this property for +resource+
@api semipublic
Returns the hash of the property name
This is necessary to allow comparisons between different properties in different models, having the same base model
@return [Integer]
the property name hash
@api semipublic
Returns index name if property has index.
@return [true, Symbol, Array, nil]
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 nil if the property does not belong to any indexes
@api public
Returns a concise string representation of the property instance.
@return [String]
Concise string representation of the property instance.
@api public
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
Returns whether or not the property is to be lazy-loaded
@return [Boolean]
true if the property is to be lazy-loaded
@api public
Returns maximum property length (if applicable). This usually only makes sense when property is of type Range or custom type.
@return [Integer, NilClass]
the maximum length of this property
@api semipublic
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
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
Returns whether or not the property is "serial" (auto-incrementing)
@return [Boolean]
whether or not the property is "serial"
@api public
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
Sets original value of the property on given resource. When property is set on DataMapper resource instance, original value is preserved. This makes possible to track dirty attributes and save only those really changed, and avoid extra queries to the data source in certain situations.
@param [Resource] resource
model instance for which to set the original value
@param [Object] original
value to set as original value for this property in +resource+
@api private
typecasts values into a primitive (Ruby class that backs DataMapper property type). If property type can handle typecasting, it is delegated. How typecasting is perfomed, depends on the primitive of the type.
If type‘s primitive is a TrueClass, values of 1, t and true are casted to true.
For String primitive, to_s is called on value.
For Float primitive, to_f is called on value but only if value is a number otherwise value is returned.
For Integer primitive, to_i is called on value but only if value is a number, otherwise value is returned.
For BigDecimal primitive, to_d is called on value but only if value is a number, otherwise value is returned.
Casting to DateTime, Time and Date can handle both hashes with keys like :day or :hour and strings in format methods like Time.parse can handle.
@param [to_s, to_f, to_i, to_d, Hash] value
the value to typecast
@return [rue, String, Float, Integer, BigDecimal, DateTime, Date, Time, Class]
The typecasted +value+
@api semipublic
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
Returns true if property has unique index. Serial properties and keys are unique by default.
@return [true, Symbol, Array, nil]
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 nil if the property does not belong to any indexes
@api public