| Class | PStore |
| In: |
lib/pstore.rb
|
| Parent: | 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 lib/pstore.rb, line 89
89: def initialize(file)
90: dir = File::dirname(file)
91: unless File::directory? dir
92: raise PStore::Error, format("directory %s does not exist", dir)
93: end
94: if File::exist? file and not File::readable? file
95: raise PStore::Error, format("file %s not readable", file)
96: end
97: @transaction = false
98: @filename = file
99: @abort = false
100: 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 PStore#transaction. It will raise PStore::Error if called at any other time.
# File lib/pstore.rb, line 123
123: def [](name)
124: in_transaction
125: @table[name]
126: 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 PStore#transaction and it cannot be read-only. It will raise PStore::Error if called at any other time.
# File lib/pstore.rb, line 168
168: def []=(name, value)
169: in_transaction_wr()
170: @table[name] = value
171: end
Ends the current PStore#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 PStore#transaction. It will raise PStore::Error if called at any other time.
# File lib/pstore.rb, line 256
256: def abort
257: in_transaction
258: @abort = true
259: throw :pstore_abort_transaction
260: end
Ends the current PStore#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 PStore#transaction. It will raise PStore::Error if called at any other time.
# File lib/pstore.rb, line 230
230: def commit
231: in_transaction
232: @abort = false
233: throw :pstore_abort_transaction
234: end
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.
# File lib/pstore.rb, line 178
178: def delete(name)
179: in_transaction_wr()
180: @table.delete name
181: end
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.
# File lib/pstore.rb, line 137
137: def fetch(name, default=PStore::Error)
138: in_transaction
139: unless @table.key? name
140: if default==PStore::Error
141: raise PStore::Error, format("undefined root name `%s'", name)
142: else
143: return default
144: end
145: end
146: @table[name]
147: end
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.
# File lib/pstore.rb, line 199
199: def root?(name)
200: in_transaction
201: @table.key? name
202: end
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.
# File lib/pstore.rb, line 189
189: def roots
190: in_transaction
191: @table.keys
192: 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 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.
# File lib/pstore.rb, line 279
279: def transaction(read_only=false) # :yields: pstore
280: raise PStore::Error, "nested transaction" if @transaction
281: begin
282: @rdonly = read_only
283: @abort = false
284: @transaction = true
285: value = nil
286: new_file = @filename + ".new"
287:
288: content = nil
289: unless read_only
290: file = File.open(@filename, File::RDWR | File::CREAT)
291: file.binmode
292: file.flock(File::LOCK_EX)
293: commit_new(file) if FileTest.exist?(new_file)
294: content = file.read()
295: else
296: begin
297: file = File.open(@filename, File::RDONLY)
298: file.binmode
299: file.flock(File::LOCK_SH)
300: content = (File.read(new_file) rescue file.read())
301: rescue Errno::ENOENT
302: content = ""
303: end
304: end
305:
306: if content != ""
307: @table = load(content)
308: if !read_only
309: size = content.size
310: md5 = Digest::MD5.digest(content)
311: end
312: else
313: @table = {}
314: end
315: content = nil # unreference huge data
316:
317: begin
318: catch(:pstore_abort_transaction) do
319: value = yield(self)
320: end
321: rescue Exception
322: @abort = true
323: raise
324: ensure
325: if !read_only and !@abort
326: tmp_file = @filename + ".tmp"
327: content = dump(@table)
328: if !md5 || size != content.size || md5 != Digest::MD5.digest(content)
329: File.open(tmp_file, "w") {|t|
330: t.binmode
331: t.write(content)
332: }
333: File.rename(tmp_file, new_file)
334: commit_new(file)
335: end
336: content = nil # unreference huge data
337: end
338: end
339: ensure
340: @table = nil
341: @transaction = false
342: file.close if file
343: end
344: value
345: end
Commits changes to the data store file.
# File lib/pstore.rb, line 364
364: def commit_new(f)
365: f.truncate(0)
366: f.rewind
367: new_file = @filename + ".new"
368: File.open(new_file) do |nf|
369: nf.binmode
370: FileUtils.copy_stream(nf, f)
371: end
372: File.unlink(new_file)
373: end
Raises PStore::Error if the calling code is not in a PStore#transaction.
# File lib/pstore.rb, line 103
103: def in_transaction
104: raise PStore::Error, "not in transaction" unless @transaction
105: end
Raises PStore::Error if the calling code is not in a PStore#transaction or if the code is in a read-only PStore#transaction.
# File lib/pstore.rb, line 110
110: def in_transaction_wr()
111: in_transaction()
112: raise PStore::Error, "in read-only transaction" if @rdonly
113: end