Results for: "pstore"

PStore implements a file based persistence 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 updated 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.

Usage 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

Transaction modes

By default, file integrity is only ensured as long as the operating system (and the underlying hardware) doesn’t raise any unexpected I/O errors. If an I/O error occurs while PStore is writing to its file, then the file will become corrupted.

You can prevent this by setting pstore.ultra_safe = true. However, this results in a minor performance loss, and only works on platforms that support atomic file renames. Please consult the documentation for ultra_safe for details.

Needless to say, if you’re storing valuable data with PStore, then you should backup the PStore files from time to time.

The error type thrown by all PStore methods.

PStore-based session storage class.

This builds upon the top-level PStore class provided by the library file pstore.rb. Session data is marshalled and stored in a file. File locking and transaction services are provided.

Ends the current PStore#transaction, discarding any changes to the data store.

Example:

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 PStore#transaction. It will raise PStore::Error if called at any other time.

To construct a PStore object, pass in the file path where you would like the data to be stored.

PStore objects are always reentrant. But if thread_safe is set to true, then it will become thread-safe at the cost of a minor performance hit.

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 PStore#transaction. It will raise PStore::Error if called at any other time.

This method is just like PStore#[], 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 PStore#transaction. It will raise PStore::Error if called at any other time.

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.

Example:

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_hierarchy] = { "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 PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.

Removes an object hierarchy from the data store, by name.

WARNING: This method is only valid in a PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.

Returns the names of all object hierarchies currently in the store.

WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.

Returns true if the supplied name is currently in the data store.

WARNING: This method is only valid in a PStore#transaction. It will raise PStore::Error if called at any other time.

Returns the path to the data store file.

Ends the current PStore#transaction, committing any changes to the data store immediately.

Example:

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 PStore#transaction. It will raise PStore::Error if called at any other time.

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 PStore#commit or PStore#abort. See those methods for details about how changes are handled. Raising an uncaught Exception in the block is equivalent to calling PStore#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.

Raises PStore::Error if the calling code is not in a PStore#transaction.

Load the given PStore file. If read_only is true, the unmarshalled Hash will be returned. If read_only is false, a 3-tuple will be returned: the unmarshalled Hash, a checksum of the data, and the size of the data.

Restore session state from the session’s PStore file.

Returns the session state as a hash.

Raises PStore::Error if the calling code is not in a PStore#transaction or if the code is in a read-only PStore#transaction.

Open the specified filename (either in read-only mode or in read-write mode) and lock it for reading or writing.

The opened File object will be returned. If read_only is true, and the file does not exist, then nil will be returned.

All exceptions are propagated.

Create a new CGI::Session::PStore instance

This constructor is used internally by CGI::Session. The user does not generally need to call it directly.

session is the session for which this instance is being created. The session id must only contain alphanumeric characters; automatically generated session ids observe this requirement.

option is a hash of options for the initializer. The following options are recognised:

tmpdir

the directory to use for storing the PStore file. Defaults to Dir::tmpdir (generally “/tmp” on Unix systems).

prefix

the prefix to add to the session id when generating the filename for this session’s PStore file. Defaults to the empty string.

This session’s PStore file will be created if it does not exist, or opened if it does.