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Move instantiation responsibilities from Inheritance to Persistence. …

…Have Inheritance#discriminate_class_for_record handle STI lookup duties.
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jeremy committed Nov 29, 2012
1 parent 7ad590d commit f2902eb8e0c382545b383cc57d46450fa3fa483f
Showing with 50 additions and 24 deletions.
  1. +24 −24 activerecord/lib/active_record/inheritance.rb
  2. +26 −0 activerecord/lib/active_record/persistence.rb
@@ -92,15 +92,6 @@ def sti_name
store_full_sti_class ? name : name.demodulize
end
- # Finder methods must instantiate through this method to work with the
- # single-table inheritance model that makes it possible to create
- # objects of different types from the same table.
- def instantiate(record, column_types = {})
- sti_class = find_sti_class(record[inheritance_column])
- column_types = sti_class.decorate_columns(column_types)
- sti_class.allocate.init_with('attributes' => record, 'column_types' => column_types)
- end
-
protected
# Returns the class type of the record using the current module as a prefix. So descendants of
@@ -132,24 +123,33 @@ def compute_type(type_name)
private
+ # Called by +instantiate+ to decide which class to use for a new
+ # record instance. For single-table inheritance, we check the record
+ # for a +type+ column and return the corresponding class.
+ def discriminate_class_for_record(record)
+ if using_single_table_inheritance?(record)
+ find_sti_class(record[inheritance_column])
+ else
+ super
+ end
+ end
+
+ def using_single_table_inheritance?(record)
+ record[inheritance_column].present? && columns_hash.include?(inheritance_column)
+ end
+
def find_sti_class(type_name)
- if type_name.blank? || !columns_hash.include?(inheritance_column)
- self
+ if store_full_sti_class
+ ActiveSupport::Dependencies.constantize(type_name)
else
- begin
- if store_full_sti_class
- ActiveSupport::Dependencies.constantize(type_name)
- else
- compute_type(type_name)
- end
- rescue NameError
- raise SubclassNotFound,
- "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
- "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
- "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
- "or overwrite #{name}.inheritance_column to use another column for that information."
- end
+ compute_type(type_name)
end
+ rescue NameError
+ raise SubclassNotFound,
+ "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
+ "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
+ "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
+ "or overwrite #{name}.inheritance_column to use another column for that information."
end
def type_condition(table = arel_table)
@@ -38,6 +38,32 @@ def create(attributes = nil, &block)
object
end
end
+
+ # Given an attributes hash, +instantiate+ returns a new instance of
+ # the appropriate class.
+ #
+ # For example, +Post.all+ may return Comments, Messages, and Emails
+ # by storing the record's subclass in a +type+ attribute. By calling
+ # +instantiate+ instead of +new+, finder methods ensure they get new
+ # instances of the appropriate class for each record.
+ #
+ # See +ActiveRecord::Inheritance#discriminate_class_for_record+ to see
+ # how this "single-table" inheritance mapping is implemented.
+ def instantiate(record, column_types = {})
+ klass = discriminate_class_for_record(record)
+ column_types = klass.decorate_columns(column_types)
+ klass.allocate.init_with('attributes' => record, 'column_types' => column_types)
+ end
+
+ private
+ # Called by +instantiate+ to decide which class to use for a new
+ # record instance.
+ #
+ # See +ActiveRecord::Inheritance#discriminate_class_for_record+ for
+ # the single-table inheritance discriminator.
+ def discriminate_class_for_record(record)
+ self
+ end
end
# Returns true if this object hasn't been saved yet -- that is, a record

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