Class: Protip::Resource::Associations::BelongsToPolymorphicAssociation

Inherits:
Object
  • Object
show all
Includes:
Association
Defined in:
lib/protip/resource/associations/belongs_to_polymorphic_association.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Association

#define_accessors!

Constructor Details

#initialize(resource_class, association_name, nested_associations, id_field: nil) ⇒ BelongsToPolymorphicAssociation

Define a polymorphic association based on a one-of field. The options for the oneof must all be IDs with an associated Protip::Resource::Associations::BelongsToAssociation that’s already been created.

Parameters:

  • resource_class (Class) —

    The Protip::Resource class that holds a reference to an associated object.

  • association_name (String) —

    The name to use when defining accessors for the associated object.

  • nested_associations (Array<Protip::Resource::Associations::BelongsToAssociation>) —

    The individual associations corresponding to the fields within the ‘oneof`.

  • id_field (Symbol|String) (defaults to: nil) —

    The name of the ‘oneof` field that holds the association ID. Defaults to `##association_name_id`.



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 21

def initialize(resource_class, association_name, nested_associations, id_field: nil)
  # The class where accessors will be defined
  @resource_class = resource_class

  # The name of the accessor methods
  @association_name = association_name.to_sym

  # The oneof field that holds the ID of the foreign resource
  @id_field  = (id_field ||
    Protip::Resource::Associations::BelongsToAssociation.default_id_field(association_name)).to_sym
  @oneof = @resource_class.message.descriptor.lookup_oneof(@id_field.to_s)
  raise "Invalid field name for polymorphic association: #{@id_field}" unless @oneof

  # Internally, keep the nested associations indexed by ID field
  @_nested_associations = {}
  nested_associations.each do |association|
    if @_nested_associations.has_key? association.id_field.to_sym
      raise ArgumentError.new("Duplicate association for #{id_field}")
    end
    @_nested_associations[association.id_field.to_sym] = association
  end
  field_names = @oneof.map{|desc| desc.name.to_sym}
  unless (field_names.length == @_nested_associations.length &&
    @_nested_associations.keys.all?{|id_field| field_names.include? id_field})
    raise ArgumentError.new(
      'Polymorphic association requires an association to be defined for all nested fields'
    )
  end
end

Instance Attribute Details

#association_name ⇒ Object (readonly)

Returns the value of attribute association_name.



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 10

def association_name
  @association_name
end

#id_field ⇒ Object (readonly)

Returns the value of attribute id_field.



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 10

def id_field
  @id_field
end

#resource_class ⇒ Object (readonly)

Returns the value of attribute resource_class.



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 10

def resource_class
  @resource_class
end

Instance Method Details

#read(resource) ⇒ Object 



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 51

def read(resource)
  field = resource.message.public_send(id_field)
  if field
    @_nested_associations[field].read(resource)
  else
    nil
  end
end

#write(resource, value) ⇒ Object 



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# File 'lib/protip/resource/associations/belongs_to_polymorphic_association.rb', line 60

def write(resource, value)
  if value == nil
    @oneof.each do |field_descriptor|
      resource.public_send(:"#{field_descriptor.name}=", nil)
    end
    nil
  else
    # Find the nested reference matching this association type
    matching_references = @_nested_associations.select do |id_field, reference|
      value.is_a? reference.associated_resource_class
    end

    # Make sure we found exactly one
    if matching_references.empty?
      raise ArgumentError.new("Could not find matching reference for value of type #{value.class}")
    end
    if matching_references.length > 1
      raise ArgumentError.new(
              "Value of type #{value.class} matched with #{matching_references.keys.map(&:to_s).join(', ')}"
            )
    end

    # And forward the write operation
    matching_references.values.first.write(resource, value)
  end
end