Class: PEROBS::ObjectBase

Inherits:
Object
  • Object
show all
Defined in:
lib/perobs/ObjectBase.rb

Overview

Base class for all persistent objects. It provides the functionality common to all classes of persistent objects.

Direct Known Subclasses

Array, Hash, Object

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(store) ⇒ ObjectBase

New PEROBS objects must always be created by calling # Store.new(). PEROBS users should never call this method or equivalents of derived methods directly.



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# File 'lib/perobs/ObjectBase.rb', line 123

def initialize(store)
  @store = store
  unless @store.object_creation_in_progress
    ::Kernel.raise ::RuntimeError,
      "All PEROBS objects must exclusively be created by calling " +
      "Store.new(). Never call the object constructor directly."
  end
  @_id = @store.db.new_id
  ObjectSpace.define_finalizer(self, ObjectBase._finalize(@store, @_id))
  @_stash_map = nil
  # Allocate a proxy object for this object. User code should only operate
  # on this proxy, never on self.
  @myself = POXReference.new(@store, @_id)

  # Let the store know that we have a modified object.
  @store.cache.cache_write(self)
end

Instance Attribute Details

#_id ⇒ Object (readonly)

Returns the value of attribute _id.



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# File 'lib/perobs/ObjectBase.rb', line 118

def _id
  @_id
end

#myself ⇒ Object (readonly)

Returns the value of attribute myself.



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# File 'lib/perobs/ObjectBase.rb', line 118

def myself
  @myself
end

#store ⇒ Object (readonly)

Returns the value of attribute store.



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# File 'lib/perobs/ObjectBase.rb', line 118

def store
  @store
end

Class Method Details

._finalize(store, id) ⇒ Object

This method generates the destructor for the objects of this class. It is done this way to prevent the Proc object hanging on to a reference to self which would prevent the object from being collected. This internal method is not intended for users to call.



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# File 'lib/perobs/ObjectBase.rb', line 145

def ObjectBase._finalize(store, id)
  proc { store._collect(id) }
end

.read(store, id) ⇒ Object

Read an raw object with the specified ID from the backing store and instantiate a new object of the specific type.



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# File 'lib/perobs/ObjectBase.rb', line 179

def ObjectBase.read(store, id)
  # Read the object from database.
  db_obj = store.db.get_object(id)

  klass = store.class_map.id_to_class(db_obj['class_id'])
  # Call the constructor of the specified class.
  obj = store._construct_po(Object.const_get(klass), id)
  obj._deserialize(db_obj['data'])
  obj.post_restore

  obj
end

Instance Method Details

#==(obj) ⇒ Object

Two objects are considered equal if their object IDs are the same.



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# File 'lib/perobs/ObjectBase.rb', line 159

def ==(obj)
  return false unless obj.is_a?(ObjectBase)
  obj && @_id == obj._id
end

#_change_id(id) ⇒ Object

Library internal method. Do not use outside of this library.



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# File 'lib/perobs/ObjectBase.rb', line 235

def _change_id(id)
  # Unregister the object with the old ID from the write cache to prevent
  # cache corruption. The objects are index by ID in the cache.
  @store.cache.unwrite(self)
  @_id = id
end

#_restore(level) ⇒ Object

Restore the object state from the storage back-end.

Parameters:

  • level (Fixnum) —

    the transaction nesting level



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# File 'lib/perobs/ObjectBase.rb', line 194

def _restore(level)
  # Find the most recently stored state of this object. This could be on
  # any previous stash level or in the regular object DB. If the object
  # was created during the transaction, there is not previous state to
  # restore to.
  id = nil
  if @_stash_map
    (level - 1).downto(0) do |lvl|
      if @_stash_map[lvl]
        id = @_stash_map[lvl]
        break
      end
    end
  end
  unless id
    if @store.db.include?(@_id)
      id = @_id
    end
  end
  if id
    db_obj = store.db.get_object(id)
    _deserialize(db_obj['data'])
  end
end

#_stash(level) ⇒ Object

Save the object state for this transaction level to the storage back-end. The object gets a new ID that is stored in @_stash_map to map the stash ID back to the original data.



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# File 'lib/perobs/ObjectBase.rb', line 222

def _stash(level)
  db_obj = {
    'class' => self.class.to_s,
    'data' => _serialize
  }
  @_stash_map = [] unless @_stash_map
  # Get a new ID to store this version of the object.
  @_stash_map[level] = stash_id = @store.db.new_id
  @store.db.put_object(db_obj, stash_id)
end

#_sync ⇒ Object

Write the object into the backing store database.



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# File 'lib/perobs/ObjectBase.rb', line 165

def _sync
  # Reset the stash map to ensure that it's reset before the next
  # transaction is being started.
  @_stash_map = nil

  db_obj = {
    'class_id' => @store.class_map.class_to_id(self.class.to_s),
    'data' => _serialize
  }
  @store.db.put_object(db_obj, @_id)
end

#post_restore ⇒ Object

This method can be overloaded by derived classes to do some massaging on the data after it has been restored from the database. This could either be some sanity check or code to migrate the object from one version to another.



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# File 'lib/perobs/ObjectBase.rb', line 155

def post_restore
end