Object
PStore implements a file based persistance mechanism based on a Hash. User code can store hierarchies of Ruby objects (values) into the data store file by name (keys). An object hierarchy may be just a single object. User code may later read values back from the data store or even update data, as needed.
The transactional behavior ensures that any changes succeed or fail together. This can be used to ensure that the data store is not left in a transitory state, where some values were upated but others were not.
Behind the scenes, Ruby objects are stored to the data store file with Marshal. That carries the usual limitations. Proc objects cannot be marshalled, for example.
require "pstore" # a mock wiki object... class WikiPage def initialize( page_name, author, contents ) @page_name = page_name @revisions = Array.new add_revision(author, contents) end attr_reader :page_name def add_revision( author, contents ) @revisions << { :created => Time.now, :author => author, :contents => contents } end def wiki_page_references [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/) end # ... end # create a new page... home_page = WikiPage.new( "HomePage", "James Edward Gray II", "A page about the JoysOfDocumentation..." ) # then we want to update page data and the index together, or not at all... wiki = PStore.new("wiki_pages.pstore") wiki.transaction do # begin transaction; do all of this or none of it # store page... wiki[home_page.page_name] = home_page # ensure that an index has been created... wiki[:wiki_index] ||= Array.new # update wiki index... wiki[:wiki_index].push(*home_page.wiki_page_references) end # commit changes to wiki data store file ### Some time later... ### # read wiki data... wiki.transaction(true) do # begin read-only transaction, no changes allowed wiki.roots.each do |data_root_name| p data_root_name p wiki[data_root_name] end end
To construct a PStore object, pass in the file path where you would like the data to be stored.
# File pstore.rb, line 94 def initialize(file) dir = File::dirname(file) unless File::directory? dir raise PStore::Error, format("directory %s does not exist", dir) end if File::exist? file and not File::readable? file raise PStore::Error, format("file %s not readable", file) end @transaction = false @filename = file @abort = false end
Retrieves a value from the PStore file data, by name. The hierarchy of Ruby objects stored under that root name will be returned.
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 128 def [](name) in_transaction @table[name] end
Stores an individual Ruby object or a hierarchy of Ruby objects in the data store file under the root name. Assigning to a name already in the data store clobbers the old data.
require "pstore" store = PStore.new("data_file.pstore") store.transaction do # begin transaction # load some data into the store... store[:single_object] = "My data..." store[:obj_heirarchy] = { "Kev Jackson" => ["rational.rb", "pstore.rb"], "James Gray" => ["erb.rb", "pstore.rb"] } end # commit changes to data store file
WARNING: This method is only valid in a #transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 173 def []=(name, value) in_transaction_wr() @table[name] = value end
Ends the current #transaction, discarding any changes to the data store.
require "pstore" store = PStore.new("data_file.pstore") store.transaction do # begin transaction store[:one] = 1 # this change is not applied, see below... store[:two] = 2 # this change is not applied, see below... store.abort # end transaction here, discard all changes store[:three] = 3 # this change is never reached end
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 261 def abort in_transaction @abort = true throw :pstore_abort_transaction end
Ends the current #transaction, committing any changes to the data store immediately.
require "pstore" store = PStore.new("data_file.pstore") store.transaction do # begin transaction # load some data into the store... store[:one] = 1 store[:two] = 2 store.commit # end transaction here, committing changes store[:three] = 3 # this change is never reached end
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 235 def commit in_transaction @abort = false throw :pstore_abort_transaction end
Removes an object hierarchy from the data store, by name.
WARNING: This method is only valid in a #transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 183 def delete(name) in_transaction_wr() @table.delete name end
This method is just like #[], save that you may also provide a default value for the object. In the event the specified name is not found in the data store, your default will be returned instead. If you do not specify a default, PStore::Error will be raised if the object is not found.
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 142 def fetch(name, default=PStore::Error) in_transaction unless @table.key? name if default==PStore::Error raise PStore::Error, format("undefined root name `%s'", name) else return default end end @table[name] end
Returns the path to the data store file.
# File pstore.rb, line 209 def path @filename end
Returns true if the supplied name is currently in the data store.
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 204 def root?(name) in_transaction @table.key? name end
Returns the names of all object hierarchies currently in the store.
WARNING: This method is only valid in a #transaction. It will raise PStore::Error if called at any other time.
# File pstore.rb, line 194 def roots in_transaction @table.keys end
Opens a new transaction for the data store. Code executed inside a block passed to this method may read and write data to and from the data store file.
At the end of the block, changes are committed to the data store automatically. You may exit the transaction early with a call to either #commit or #abort. See those methods for details about how changes are handled. Raising an uncaught Exception in the block is equivalent to calling #abort.
If read_only is set to true
, you will only be allowed
to read from the data store during the transaction and any attempts to
change the data will raise a PStore::Error.
Note that PStore does not support nested transactions.
# File pstore.rb, line 284 def transaction(read_only=false) # :yields: pstore raise PStore::Error, "nested transaction" if @transaction begin @rdonly = read_only @abort = false @transaction = true value = nil new_file = @filename + ".new" content = nil unless read_only file = File.open(@filename, RDWR_ACCESS) file.flock(File::LOCK_EX) commit_new(file) if FileTest.exist?(new_file) content = file.read() else begin file = File.open(@filename, RD_ACCESS) file.flock(File::LOCK_SH) content = (File.open(new_file, RD_ACCESS) {|n| n.read} rescue file.read()) rescue Errno::ENOENT content = "" end end if content != "" @table = load(content) if !read_only size = content.size md5 = Digest::MD5.digest(content) end else @table = {} end content = nil # unreference huge data begin catch(:pstore_abort_transaction) do value = yield(self) end rescue Exception @abort = true raise ensure if !read_only and !@abort tmp_file = @filename + ".tmp" content = dump(@table) if !md5 || size != content.size || md5 != Digest::MD5.digest(content) File.open(tmp_file, WR_ACCESS) {|t| t.write(content)} File.rename(tmp_file, new_file) commit_new(file) end content = nil # unreference huge data end end ensure @table = nil @transaction = false file.close if file end value end