- Inheritance
- < 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.
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
Classes & Modules
Constants
| Name | Description | |
|---|---|---|
| RDWR_ACCESS | = File::RDWR | File::CREAT | binmode | |
| RD_ACCESS | = File::RDONLY | binmode | |
| WR_ACCESS | = File::WRONLY | File::CREAT | File::TRUNC | binmode |
Methods
Class
| Visibility | Signature |
|---|---|
| public | new (file) |
Instance
| Visibility | Signature |
|---|---|
| public | [] (name) |
| public | []= (name, value) |
| public | abort () |
| public | commit () |
| public | delete (name) |
| public | fetch (name, default=PStore::Error) |
| public | path () |
| public | root? (name) |
| public | roots () |
| public | transaction (read_only=false) {|pstore| ...} |
Class Method Detail
new(file)
Instance Method Detail
[](name)
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.
[]=(name, value)
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_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 PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
abort()
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.
commit()
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.
delete(name)
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.
fetch(name, default=PStore::Error)
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.
path()
Returns the path to the data store file.
root?(name)
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.
roots()
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.
transaction(read_only=false) {|pstore| ...}
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.