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U:RDoc::NormalClass[iI"PStore:ET@I"Object;To:RDoc::Markup::Document:@parts[o;;[ho:RDoc::Markup::Paragraph;[I"L\PStore implements a file based persistence mechanism based on a Hash. ;TI">User code can store hierarchies of Ruby objects (values) ;TI")into the data store by name (keys). ;TI"6An object hierarchy may be just a single object. ;TI">User code may later read values back from the data store ;TI"$or even update data, as needed.;To:RDoc::Markup::BlankLine�o;	;[I"SThe transactional behavior ensures that any changes succeed or fail together. ;TI"WThis can be used to ensure that the data store is not left in a transitory state, ;TI"8where some values were updated but others were not.;T@o;	;[I"UBehind the scenes, Ruby objects are stored to the data store file with Marshal. ;TI"LThat carries the usual limitations. Proc objects cannot be marshalled, ;TI"for example.;T@o;	;[I"DThere are three important concepts here (details at the links):;T@o:RDoc::Markup::List:
@type:BULLET:@items[o:RDoc::Markup::ListItem:@label0;[o;	;[I"K{Store}[rdoc-ref:PStore@The+Store]: a store is an instance of \PStore.;To;;0;[o;	;[I"A{Entries}[rdoc-ref:PStore@Entries]: the store is hash-like; ;TI"/each entry is the key for a stored object.;To;;0;[o;	;[	I"T{Transactions}[rdoc-ref:PStore@Transactions]: each transaction is a collection ;TI"*of prospective changes to the store; ;TI"=a transaction is defined in the block given with a call ;TI"to PStore#transaction.;T@S:RDoc::Markup::Heading:
leveli:	textI"About the Examples;T@o;	;[I"CExamples on this page need a store that has known properties. ;TI">They can get a new (and populated) store by calling thus:;T@o:RDoc::Markup::Verbatim;[I"example_store do |store|
;TI"-  # Example code using store goes here.
;TI"	end
;T:@format0o;	;[I"6All we really need to know about +example_store+ ;TI"Iis that it yields a fresh store with a known population of entries; ;TI"its implementation:;T@o;;[I"require 'pstore'
;TI"require 'tempfile'
;TI"3# Yield a pristine store for use in examples.
;TI"def example_store
;TI"/  # Create the store in a temporary file.
;TI"!  Tempfile.create do |file|
;TI""    store = PStore.new(file)
;TI"    # Populate the store.
;TI"    store.transaction do
;TI"      store[:foo] = 0
;TI"      store[:bar] = 1
;TI"      store[:baz] = 2
;TI"
    end
;TI"    yield store
;TI"  end
;TI"	end
;T;0S;;i;I"The Store;T@o;	;[
I"PThe contents of the store are maintained in a file whose path is specified ;TI"1when the store is created (see PStore.new). ;TI"0The objects are stored and retrieved using ;TI"Tmodule Marshal, which means that certain objects cannot be added to the store; ;TI"0see {Marshal::dump}[rdoc-ref:Marshal.dump].;T@S;;i;I"Entries;T@o;	;[I"-A store may have any number of entries. ;TI"9Each entry has a key and a value, just as in a hash:;T@o;;;
;[o;;0;[o;	;[	I"<Key: as in a hash, the key can be (almost) any object; ;TI"/see {Hash Keys}[rdoc-ref:Hash@Hash+Keys]. ;TI"@You may find it convenient to keep it simple by using only ;TI" symbols or strings as keys.;To;;0;[o;	;[
I"KValue: the value may be any object that can be marshalled by \Marshal ;TI"2(see {Marshal::dump}[rdoc-ref:Marshal.dump]) ;TI"%and in fact may be a collection ;TI"4(e.g., an array, a hash, a set, a range, etc). ;TI"9That collection may in turn contain nested objects, ;TI"*including collections, to any depth; ;TI"/those objects must also be \Marshal-able. ;TI"DSee {Hierarchical Values}[rdoc-ref:PStore@Hierarchical+Values].;T@S;;i;I"Transactions;T@S;;i;I"The Transaction Block;T@o;	;[I"9The block given with a call to method #transaction# ;TI"contains a _transaction_, ;TI"5which consists of calls to \PStore methods that ;TI"%read from or write to the store ;TI"?(that is, all \PStore methods except #transaction itself, ;TI"#path, and Pstore.new):;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI",    store.keys # => [:foo, :bar, :baz]
;TI"    store[:bat] = 3
;TI"2    store.keys # => [:foo, :bar, :baz, :bat]
;TI"  end
;TI"	end
;T;0o;	;[	I"EExecution of the transaction is deferred until the block exits, ;TI"4and is executed _atomically_ (all-or-nothing): ;TI"=either all transaction calls are executed, or none are. ;TI"/This maintains the integrity of the store.;T@o;	;[I"LOther code in the block (including even calls to #path and PStore.new) ;TI"+is executed immediately, not deferred.;T@o;	;[I"The transaction block:;T@o;;;
;[o;;0;[o;	;[I"3May not contain a nested call to #transaction.;To;;0;[o;	;[I"BIs the only context where methods that read from or write to ;TI"the store are allowed.;T@o;	;[I"DAs seen above, changes in a transaction are made automatically ;TI"when the block exits. ;TI"GThe block may be exited early by calling method #commit or #abort.;T@o;;;
;[o;;0;[o;	;[I"IMethod #commit triggers the update to the store and exits the block:;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI",    store.keys # => [:foo, :bar, :baz]
;TI"    store[:bat] = 3
;TI"    store.commit
;TI"     fail 'Cannot get here'
;TI"  end
;TI"  store.transaction do
;TI"!    # Update was completed.
;TI"2    store.keys # => [:foo, :bar, :baz, :bat]
;TI"  end
;TI"	end
;T;0o;;0;[o;	;[I"HMethod #abort discards the update to the store and exits the block:;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI",    store.keys # => [:foo, :bar, :baz]
;TI"    store[:bat] = 3
;TI"    store.abort
;TI"     fail 'Cannot get here'
;TI"  end
;TI"  store.transaction do
;TI"%    # Update was not completed.
;TI",    store.keys # => [:foo, :bar, :baz]
;TI"  end
;TI"	end
;T;0S;;i;I"Read-Only Transactions;T@o;	;[I"GBy default, a transaction allows both reading from and writing to ;TI"the store:;T@o;;[	I"store.transaction do
;TI"!  # Read-write transaction.
;TI"A  # Any code except a call to #transaction is allowed here.
;TI"	end
;T;0o;	;[I"2If argument +read_only+ is passed as +true+, ;TI"only reading is allowed:;T@o;;[	I" store.transaction(true) do
;TI"   # Read-only transaction:
;TI"H  # Calls to #transaction, #[]=, and #delete are not allowed here.
;TI"	end
;T;0S;;i;I"Hierarchical Values;T@o;	;[I"DThe value for an entry may be a simple object (as seen above). ;TI"?It may also be a hierarchy of objects nested to any depth:;T@o;;[I"+deep_store = PStore.new('deep.store')
;TI"deep_store.transaction do
;TI"&  array_of_hashes = [{}, {}, {}]
;TI"6  deep_store[:array_of_hashes] = array_of_hashes
;TI"6  deep_store[:array_of_hashes] # => [{}, {}, {}]
;TI"4  hash_of_arrays = {foo: [], bar: [], baz: []}
;TI"4  deep_store[:hash_of_arrays] = hash_of_arrays
;TI"H  deep_store[:hash_of_arrays]  # => {:foo=>[], :bar=>[], :baz=>[]}
;TI"4  deep_store[:hash_of_arrays][:foo].push(:bat)
;TI"L  deep_store[:hash_of_arrays]  # => {:foo=>[:bat], :bar=>[], :baz=>[]}
;TI"	end
;T;0o;	;[I"!And recall that you can use ;TI".{dig methods}[rdoc-ref:dig_methods.rdoc] ;TI"(in a returned hierarchy of objects.;T@S;;i;I"Working with the Store;T@S;;i;I"Creating a Store;T@o;	;[I".Use method PStore.new to create a store. ;TI"8The new store creates or opens its containing file:;T@o;;[I"#store = PStore.new('t.store')
;T;0S;;i;I"Modifying the Store;T@o;	;[I"2Use method #[]= to update or create an entry:;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI"#    store[:foo] = 1 # Update.
;TI"#    store[:bam] = 1 # Create.
;TI"  end
;TI"	end
;T;0o;	;[I"+Use method #delete to remove an entry:;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI"    store.delete(:foo)
;TI"    store[:foo] # => nil
;TI"  end
;TI"	end
;T;0S;;i;I"Retrieving Values;T@o;	;[I"CUse method #fetch (allows default) or #[] (defaults to +nil+) ;TI"to retrieve an entry:;T@o;;[I"example_store do |store|
;TI"  store.transaction do
;TI"(    store[:foo]             # => 0
;TI"*    store[:nope]            # => nil
;TI"(    store.fetch(:baz)       # => 2
;TI"*    store.fetch(:nope, nil) # => nil
;TI"5    store.fetch(:nope)      # Raises exception.
;TI"  end
;TI"	end
;T;0S;;i;I"Querying the Store;T@o;	;[I">Use method #key? to determine whether a given key exists:;T@o;;[
I"example_store do |store|
;TI"  store.transaction do
;TI"$    store.key?(:foo) # => true
;TI"  end
;TI"	end
;T;0o;	;[I"'Use method #keys to retrieve keys:;T@o;;[
I"example_store do |store|
;TI"  store.transaction do
;TI",    store.keys # => [:foo, :bar, :baz]
;TI"  end
;TI"	end
;T;0o;	;[I"KUse method #path to retrieve the path to the store's underlying file; ;TI"@this method may be called from outside a transaction block:;T@o;;[I"#store = PStore.new('t.store')
;TI"store.path # => "t.store"
;T;0S;;i;I"Transaction Safety;T@o;	;[I"!For transaction safety, see:;T@o;;;
;[o;;0;[o;	;[I":Optional argument +thread_safe+ at method PStore.new.;To;;0;[o;	;[I"Attribute #ultra_safe.;T@o;	;[I"TNeedless to say, if you're storing valuable data with \PStore, then you should ;TI"/backup the \PStore file from time to time.;T@S;;i;I"An Example Store;T@o;;[4I"require "pstore"
;TI"
;TI"# A mock wiki object.
;TI"class WikiPage
;TI"
;TI"  attr_reader :page_name
;TI"
;TI"3  def initialize(page_name, author, contents)
;TI"     @page_name = page_name
;TI"     @revisions = Array.new
;TI"(    add_revision(author, contents)
;TI"  end
;TI"
;TI"*  def add_revision(author, contents)
;TI"+    @revisions << {created: Time.now,
;TI"(                   author: author,
;TI",                   contents: contents}
;TI"  end
;TI"
;TI"   def wiki_page_references
;TI"R    [@page_name] + @revisions.last[:contents].scan(/\b(?:[A-Z]+[a-z]+){2,}/)
;TI"  end
;TI"
;TI"	end
;TI"
;TI"# Create a new wiki page.
;TI"Bhome_page = WikiPage.new("HomePage", "James Edward Gray II",
;TI"J                         "A page about the JoysOfDocumentation..." )
;TI"
;TI",wiki = PStore.new("wiki_pages.pstore")
;TI"?# Update page data and the index together, or not at all.
;TI"wiki.transaction do
;TI"  # Store page.
;TI"-  wiki[home_page.page_name] = home_page
;TI"  # Create page index.
;TI"'  wiki[:wiki_index] ||= Array.new
;TI"  # Update wiki index.
;TI"?  wiki[:wiki_index].push(*home_page.wiki_page_references)
;TI"	end
;TI"
;TI";# Read wiki data, setting argument read_only to true.
;TI"wiki.transaction(true) do
;TI"  wiki.keys.each do |key|
;TI"    puts key
;TI"    puts wiki[key]
;TI"  end
;TI"end;T;0:
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