Now we have a named method available to use on the people collection in Java

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Now we have a named method available to use on the people collection
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person = Accountfirstpeoplenamed("David Heinemeier Hansson") personfirst_name # => "David" personlast_name # => "Heinemeier Hansson"
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If you need to share the same set of extensions between many associations, you can use specify an extension module, instead of a block with method definitions Here is the same feature shown in Listing 75, except broken out into its own Ruby module:
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module ByNameExtension def named(full_name) first_name, last_name = full_namesplit(" ", 2) find_or_create_by_first_name_and_last_name(first_name, last_name) end end
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Now we can use it to extend many different relationships, as long as they re compatible (Our contract in the example consists of the find_or_create_by_first_name_and_ last_name method)
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class Account < ActiveRecord::Base has_many :people, :extend => ByNameExtension end class Company < ActiveRecord::Base has_many :people, :extend => ByNameExtension end
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If you need to use multiple named extension modules, you can pass an array of modules to the :extend option instead of a single module, like this:
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has_many :people, :extend => [ByNameExtension, ByRecentExtension]
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In the case of name conflicts, methods contained in modules added later in the array supercede those earlier in the array
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79 The AssociationProxy Class
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Consider a class method instead
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Unless you have a valid reason to reuse the extension logic with more than one type of model, you re probably better off leveraging the fact that class methods are automatically available on has_many associations
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class Person < ActiveRecord::Base belongs_to :account def selfnamed(full_name) first_name, last_name = full_namesplit(" ", 2) find_or_create_by_first_name_and_last_name(first_name, last_name) end end
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79 The AssociationProxy Class
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AssociationProxy, the parent of all association proxies (refer to Figure 71 if needed),
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Active Record
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contributes a handful of useful methods that apply to most kinds of associations and can come into play when you re writing association extensions
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proxy owner, proxy reflection, and proxy target
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References to the internal owner, reflection, and target attributes of the association proxy, respectively The proxy_owner method provides a reference to the parent object holding the association The proxy_reflection object is an instance of ActiveRecord::Reflection:: AssociationReflection and contains all of the configuration options for the association That includes both default settings and those that were passed to the association method when it was declared5 Finally, the proxy_target is the associated array (or associated object itself in the case of belongs_to and has_one) It might not appear sane to expose these attributes publicly and allow their manipulation However, without access to them it would be much more difficult to write advanced association extensions The loaded , loaded, target, and target= methods are public for similar reasons
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5 To learn more about how the reflection object can be useful, including an explanation on how to establish has_many :through associations via other has_many :through associations, check out the must-read article: http://wwwpivotalblabscom/articles/2007/08/26/ten-things-i-hate-aboutproxy-objects-part-i
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7: Active Record Associations
The following code sample demonstrates the use of proxy_owner within a
published_prior_to extension method, originally contributed by Wilson Bilkovich:
class ArticleCategory < ActiveRecord::Base acts_as_tree has_many :articles do def published_prior_to(date, options = {}) if proxy_ownertop_level Articlewhere('published_at < and category_id = ', date, proxy_owner) else # self is the 'articles' association here so we inherit its scope selfall(options) end end end def top_level # do we have a parent, and is our parent the root node of the tree selfparent && selfparentparentnil end end
The acts_as_tree Active Record plugin extension creates a self-referential association based on a parent_id column The proxy_owner reference is used to check if the parent of this association is a top-level node in the tree
reload and reset
The reset method puts the association proxy back in its initial state, which is unloaded (cached association objects are cleared) The reload method invokes reset, and then loads associated objects from the database
710 Conclusion
The ability to model associations is what makes Active Record more than just a dataaccess layer The ease and elegance with which you can declare those associations are what make Active Record more than your ordinary object-relational mapper In this chapter, we covered the basics of how Active Record associations work We started by taking a look at the class hierarchy of associations classes, starting with AssociationProxy Hopefully, by learning about how associations work under the hood, you ve picked up some enhanced understanding about their power and flexibility Finally, the options and methods guide for each type of association should be a good reference guide for your day-to-day development activities