Reusable code that treats TWiki forms data as if it were a database

Summary of Contents

This module supports structured queries over a database built on the fly from the forms in TWiki topics. It does not support any tags, as it is provided as a service for other plugins that want to treat a TWiki web as a simple database; for example, the TWiki:Plugins/FormQueryPlugin, which supports the display of query results.

The plugin encapsulates code that was formerly in the "engine room" of the FormQueryPlugin. It has been abstracted out in the belief that it will be useful to anyone who wants to do simple search operations from a plugin.

Features

• Perform complex queries on the TWiki database
• Cache TWiki topics for rapid queries

How the database gets built

You can think of the database as an array of all the topics in a web. Each array entry is a map (or hash in perl terms) that maps a set of field names to values.

Each topic in the web automatically gets a number of standard fields, generated by reading data and metadata (see TWikiMetaData^?) from the topic:

• name - name of the topic
• parent - name of parent topic
• web - name of the topic web
• _up - reference to the Map of the parent topic, if it exists
• attachments - array of Maps, each of which contains:
  • _up - reference to the Map for the topic
  • name - attachment name
  • attr - e.g hidden
  • comment - attachment comment
  • path - client path used to upload attachment
  • size - size in Kb
  • user - who uploaded the attachment
  • version - e.g. 1.3
• info - Map containing:
  • _up - reference to the Map for the topic
  • author - most recent author
  • date - date of last change
  • format - topic format version
  • version - topic version number
• moved - Map containing:
  • _up - reference to the Map for the topic
  • by - who moved it
  • date - when they moved it
  • from - where they moved it from
  • to - where they moved it to
• form - form name
• form name - (e.g. if a Form named "MyForm" is attached, this will be MyForm); a Map containing:
  • _up - reference to the Map for the topic
  • a key for each field in the form (see TWikiForms^?) mapping to the value in the form data for that key
• text - raw text of the topic

Reminder: The sub-Maps created for info, form name, moved, and each row in attachments also have a reference back to the topic Map, called _up.

Other fields may be added by subclasses. Refer to the documentation for clients of DBCacheContrib for more details.

The cache

To achieve best performance the plugin caches the database read from the TWiki topics. It creates this cache in a file in the web, _DBCache, albeit the file name can be overridden in a descendant. If any topic changes in the web this cache is automatically rebuilt. The cache file can be deleted at any point with no ill effects.

Extending or customising

Extension or customisation is welcome, as long as all extensions are described and code provided back to the author.

The module is shipped with a perl build file, which should be used for installation and testing. Testing is done using Test::Unit, and is invoked using the 'test' build target. Writing tests is a useful way of feeding back bugs as well. I can't encourage you enough to maintain and extend the tests!

Detailed Documentation

Clients use the DBCache by defining a subclass of the TWiki::Contrib::DBCache class. The following POD documentation describes the methods of this class and the various other classes provided by the plugin..

class DBCache

General purpose cache that treats TWiki topics as hashes. Useful for rapid read and search of the database. Only works on one web.

Typical usage:

  use TWiki::Contrib::DBCache;

  $db = new TWiki::Contrib::DBCache( $web ); # always done
  $db->load(); # may be always done, or only on demand when a tag is parsed that needs it

  # the DB is a hash of topics keyed on their name
  foreach my $topic ($db->getKeys()) {
     my $attachments = $db->get($topic)->get("attachments");
     # attachments is an array
     foreach my $val ($attachments->getValues()) {
       my $aname = $attachments->get("name");
       my $acomment = $attachments->get("comment");
       my $adate = $attachments->get("date");
       ...
     }
  }

As topics are loaded, the readTopicLine method gives subclasses an opportunity to apply special processing to indivual lines, for example to extract special syntax such as %ACTION lines, or embedded tables in the text. See FormQueryPlugin for an example of this.

new($dataDir, $web)

• $dataDir - location of cache file
• $web - name of web to create the object for.

Construct a new DBCache object.

readTopicLine($topic, $meta, $line, $fh) -> text

• $topic - name of the topic being read
• $meta - reference to the hash object for this topic
• line - the line being read
• $fh - the file handle of the file
• return text to insert in place of line in the text field of the topic

Called when reading a topic that is being cached, this method is invoked on each line in the topic. It is designed to be overridden by subclasses; the default implementation does nothing. The sort of expected activities will be (for example) reading tables and adding them to the hash for the topic.

onReload($topics)

• $topics - perl array of topic names that have just been loaded (or reloaded)

Designed to be overridden by subclasses. Called when one or more topics had to be read from disc rather than from the cache. Passed a list of topic names that have been read.

load()

Load the web into the database. Returns a string containing 3 numbers that give the number of topics read from the cache, the number read from file, and the number of previously cached topics that have been removed.

write($archive)

• $archive - the TWiki::Contrib::Archive being written to

Writes this object to the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

read($archive)

• $archive - the TWiki::Contrib::Archive being read from

Reads this object from the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

class Search

Search operators work on the fields of a TWiki::Contrib::Map. The fields are given by their name, and values by strings. Strings are surrounded by single quotes. Strings may be regular expressions and use 'perl' re syntax (see man perlre for help). An embedded search may also be applied to a field value. In addition, the left-hand and right-hand sides of a search expression may also by of the form $CALC( text ), where text is some text string surrounded by quotes which is evaluated by the SpreadSheetPlugin. The special operator $T interprets its single argument as a field expression. (The quotes need to be escaped if within a string.)

Warning single and double quotes are not allowed in values!

The following operators are available:

Operator	LHS	RHS	Meaning
l = r	field name or calc	regular expression string or field name or calc	Value exactly matches this regular expression. The expression must match the whole string.
l != r	field name or calc	regular expression string or field name or calc	Field is not this RE. Inverse of =
l =~ r	field name or calc	regular expression string or field name or calc	Value contains this regular expression i.e. the RE is found somewhere in the field value.
l < r	field name or calc	integer (string containing an integer e.g '4')	field value is < integer
l > r	field name or calc	integer	field value is > integer
l >= r	field name or calc	integer	field value is >= integer
l <= r	field name or calc	integer	field value is <= integer
l [? r ]	field name	search expression	search applied to field value

A search string consisting of text somestring without any operator is interpreted as the string text=~'somestring'.

A search string consisting of a single =%CALC% expression is interpreted as a test of the result of the expression.

Searches may be combined by the following logical operators:

Operator	LHS	RHS	Meaning
AND	expr	expr	Boolean AND
OR	expr	expr	Boolean OR
()	N/A	N/A	Bracketed subexpression
!	none	expr	Boolean NOT

A search object implements the "matches" method as its general contract with the rest of the world.

Example

Get a list of attachments that have a date earlier than 1st January 2000

  $db = new TWiki::Contrib::DBCache( $web ); # always done
  $db->load();
  my $search = new TWiki::Contrib::Search("date EARLIER_THAN '1st January 2000'");

  foreach my $topic ($db->getKeys()) {
     my $attachments = $topic->get("attachments");
     foreach my $val ($attachments->getValues()) {
       if ($search->matches($val)) {
          print $val->get("name") . "\n";
       }
     }
  }

create($string)

• $string - string containing an expression to parse

Construct a new search node by parsing the passed expression.

matches($object, $case) -> boolean

• $object - object to test; must implement get
• $case - boolean flag; the match is casesensitive if true

See if object matches the search. $object can be any object that provides the method "get" that returns a value given a string key.

toString() -> string

Generates a string representation of the object.

class FileTime

Object that handles a file/time tuple for use in Storable and TWiki::Contrib::Archive.

new($file)

• $file - filename

Construct from a file name

uptodate() -> boolean

Check the file time against what is seen on disc. Return 1 if consistent, 0 if inconsistent.

toString() -> string

Generates a string representation of the object.

write()

TWiki::Contrib::Archive hook

read()

TWiki::Contrib::Archive hook

class Array

Generic array object. This is required because perl arrays are not objects, and cannot be subclassed e.g. for serialisation. To avoid lots of horrid code to handle special cases of the different perl data structures, we use this array object instead.

new()

Create a new, empty array object

add($object)

• $object any perl data type

Add an element to the end of the array

find($object) -> integer

• $object datum of the same type as the content of the array

Uses "==" to find the given element in the array and return it's index

remove($index)

• $index - integer index

Remove an entry at an index from the array.

get($key, $root) -> datum

• $k - key
• $root - what # refers to

Subfield syntax

• get("9", $r) where $n is a number will get the 9th entry in the array
• get("[9]", $r) will also get the 9th entry
• get(".X", $r) will return the sum of the subfield X of each entry
• get("[?search]", $r) will perform the given search over the entries in the array. Always returns an array result, even when there is only one result. For example: [?name='Sam'] will return an array of all the entries that have their subfield name set to Sam.
• # means "reset to root". So get("#[3]", $r) will return the 4th entry of $r (assuming $r is an array!).
• get("[*X]", $r) will get a new array made from subfield X of each entry in this array.

Where the result of a subfield expansion is another object (a Map or an Array) then further subfield expansions can be used. For example,

get("parent.UserTable[?SubTopic='ThisTopic'].UserName", $web);

See also TWiki::Contrib::Map for syntax that applies to maps.

size() -> integer

Get the size of the array

sum($field) -> number

• $field - name of a field in the class of objects stored by this array

Returns the sum of values of the given field in the objects stored in this array.

search($search, $case) -> search result

• $search TWiki::Contrib::Search object to use in the search
• $case - boolean flag; the match is casesensitive if true

Search the array for matches with the given object. values. Return a TWiki::Contrib::Array of matching entries.

getValues() -> perl array

Get a "perl" array of the values in the array, suitable for use with foreach

toString($limit, $level, $strung) -> string

• $limit - recursion limit for expansion of elements
• $level - currentl recursion level

Generates an HTML string representation of the object.

write($archive)

• $archive - the TWiki::Contrib::Archive being written to

Writes this object to the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

read($archive)

• $archive - the TWiki::Contrib::Archive being read from

Reads this object from the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

class Map

Generic map object for mapping names to things. A name is defined as name = \w+ | \w+ "." name The . indicates a field reference in a sub-map. Objects in the map are either strings, or other objects that must support toString.

new($string)

• $string - optional attribute string in standard TWiki syntax

Create a new, empty array object. Optionally parse a standard attribute string containing name=value pairs. The value may be a word or a quoted string (no escapes!)

fastget($k) -> datum

• $k - key

Get the value for a key, but without any subfield field expansion

get($k, $root) -> datum

• $k - key
• $root what # refers to

Get the value corresponding to key $k; return undef if not set.

Subfield syntax

• get("X",$r) will get the subfield named X.
• get("X.Y",$r) will get the subfield Y of the subfield named X.
• # means "reset to root". So get("#.Y", $r) will return the subfield Y of $r (assuming $r is a map!).

Where the result of a subfield expansion is another object (a Map or an Array) then further subfield expansions can be used. For example,

get("UserTable[0].Surname", $web);

See also TWiki::Contrib::Array for syntax that applies to arrays.

set($k, $v)

• $k - key
• $v - value

Set the given key, value pair in the map.

size() -> integer

Get the size of the map

remove($index) -> old value

• $index - integer index

Remove an entry at an index from the array. Return the old value.

getKeys() -> perl array

Get a "perl" array of the keys in the map, suitable for use with foreach

getValues() -> perl array

Get a "perl" array of the values in the Map, suitable for use with foreach

search($search, $case) -> search result

• $search - TWiki::Contrib::Search object to use in the search
• $case - boolean flag; the match is casesensitive if true

Search the map for keys that match with the given object. values. Return a TWiki::Contrib::Array of matching keys.

toString($limit, $level, $strung) -> string

• $limit - recursion limit for expansion of elements
• $level - currentl recursion level

Generates an HTML string representation of the object.

write($archive)

• $archive - the TWiki::Contrib::Archive being written to

Writes this object to the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

read($archive)

• $archive - the TWiki::Contrib::Archive being read from

Reads this object from the archive. Archives are used only if Storable is not available. This method must be overridden by subclasses is serialisation of their data fields is required.

class Archive

Simple file archive storer and restorer. Handles serialising objects using their "write" and "read" methods. Serialisable objects must have a no-parameters constructor.

This module is only used if Storable isn't available. Storable is much faster, because it is implemented in C.

new($file, $rw)

• $file - archive file path
• $rw - mode "r" or "w"

Create a new archive, using filename $file and mode $rw which must be "r" or "w". The archive will remain in existence (and the file remain open) until "close" is called. An exclusive lock is taken for write as long as the file is open. Throws an exception if the archive cannot be opened.

close()

Close this archive. MUST be called to close the file.

writeByte($b)

• $b - byte to write

Write a byte to the archive

writeString($s)

• $s - string to write

Write a string to the archive

writeInt($i)

• $i integer to write

Write a 32-bit integer to the archive

writeObject()

Write an object to the archive. An object must implement read($archive) and write($archive), or may be undef or a string. No other types are supported.

readByte() -> byte

Read a byte from the archive

readString() -> string

Read a UTF8 string from the archive

readInt() -> integer

Read a 32-bit integer from the archive

readObject() -> object

Read an object from the archive

Settings

• Name of the perl package
  • Set STUB = TWiki::Contrib::DBCache

Installation Instructions

• Download the ZIP file from the Plugin web (see below). Contents:

  File:	Description:
  lib/TWiki/Contrib/DBCache.pm	Web cache class
  lib/TWiki/Contrib/Search.pm	Search object and parser
  lib/TWiki/Contrib/Search.yp	Source file for the parser. Search.pm can be generated by yapp -s Search.yp, if yapp is installed.
  lib/TWiki/Contrib/FileTime.pm	Cache support for remembering file dates
  lib/TWiki/Contrib/Array.pm	Array class
  lib/TWiki/Contrib/Map.pm	Map class
  lib/TWiki/Contrib/Archive.pm	Archiver used if Storable is not available
  lib/TWiki/Contrib/DBCacheContrib/build.pl	Build file
  lib/TWiki/Contrib/DBCacheContrib/test.zip	Test::Unit tests
  data/TWiki/DBCacheContrib.txt	Documentation topic
  DBCacheContrib_installer.pl	Install script

• Unzip DBCacheContrib.zip in your twiki installation directory.
• Optionally, run DBCacheContrib_installer to automatically check and install other TWiki modules that this module depends on. You can also do this step manually.
• Alternatively, manually make sure the dependencies listed in the table below are resolved.

Contrib Info

Author:	TWiki:Main/CrawfordCurrie, TWiki:Main/ThomasWeigert
Copyright ©:	This code is based on an original development of Motorola Inc. and is protected by the following copyrights: Copyright © 2002-2003, 2005 Motorola Inc. All Rights Reserved. Portions copyright © 2004. Crawford Currie http://www.c-dot.co.uk
License:	As required for the publication of all extensions to TWiki, this software is published under the terms of the GNU General Public License. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details, published at http://www.gnu.org/copyleft/gpl.html
Version:	1.002
Change History:	9 Jul 2005: Fixed updating of parents when reloading from m cache. 4 Jul 2005: Replaced date operators by the ability to leverage the SpreadSheetPlugin. 10 Jun 2005: Replaced parser with LALR-1 table driven parser. Store web information in cache. Fix summing of subfields, expansion of fields, [? search ] syntax, array notation. Empty search matches the whole data base (consistent with %SEARCH%).
	8 Jul 2004: Initial version, split out from FormQueryPlugin
Dependencies:	Name Version Description TWiki::Contrib::Attrs >=1.000 Required. Download and install from the TWiki:Plugins/AttrsContrib code library. TWiki::Plugins::SpreadSheetPlugin   Required. Download and install TWiki:Plugins/SpreadSheetPlugin Storable >=2.07 Recommended; accelerates cache handling. Available from CPAN
Perl Version:	5.0
Plugin Home:	http://TWiki.org/cgi-bin/view/Plugins/DBCacheContrib
Feedback:	http://TWiki.org/cgi-bin/view/Plugins/DBCacheContribDev
Demo URL:

-- TWiki:Main/ThomasWeigert - 09 Jul 2005