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DBCacheContrib

Reusable code that treats TWiki forms as if they were table rows in 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 the metadata from the topic (see TWikiMetaData)

  • name - name of the topic
  • parent - name of parent topic
  • _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 type
  • form name - e.g. if a "MyForm" is attached, this will be MyForm. This is a reference to a Map containing a key for each field in the form. Each key maps to the value in the form data for that key. The Map will also have an _up reference to the Map for the topic.
  • text - raw text of the topic)

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 the plugin that is using the DBCache for more details.

The cache

To achieve best perfomance the plugin caches the database read from the TWiki topics. The cache is stored in the work area for the DBCacheContrib (see {RCS}{WorkAreaDir} in configure). 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 CPAN: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::DBCacheContrib class. The following POD documentation describes the methods of this class and the various other classes provided by the plugin..

class DBCacheContrib

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::DBCacheContrib;

  $db = new TWiki::Contrib::DBCacheContrib( $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($web, $cacheName)

  • $web name of web to create the object for.
  • $cacheName name of cache file (default "_DBCache")

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( [updateCache] ) -> ($readFromCache, $readFromFile, $removed)

Load the web into the database. Returns a list 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.

if $TWiki::cfg{DBCache}{AlwaysUpdateCache} is set to FALSE (defaults to TRUE for compatibility) then avoid calling _updateCache unless requested. DBCachePlugin now only asked for it from the afterSaveHandler and from the new REST updateCache handler

package TWiki::Contrib::DBCacheContrib::Search

Search operators work on the fields of a TWiki::Contrib::DBCacheContrib::Map.

Fields are given by name, and values by strings or numbers. Strings should always be surrounded by 'single-quotes'. Strings which are regular expressions (RHS of , ~ operators) use 'perl' regular expression syntax (google for =perlre for help). Numbers can be signed integers or decimals. Single quotes in values may be escaped using backslash (\).

The following operators are available:

Operator Result Meaning
= Boolean LHS exactly matches the regular expression on the RHS. The expression must match the whole string.
!= Boolean Inverse of =
=~ Boolean LHS contains RHS i.e. the RHS is found somewhere in the field value.
< Boolean Numeric <
> Boolean Numeric >
>= Boolean Numeric >=
<= Boolean Numeric <=
lc String Unary lower case
uc String Unary UPPER CASE
EARLIER_THAN BOOLEAN Date is earlier than the given date
LATER_THAN Boolean LHS is later than the given date (string containing a date e.g. '1 Apr 2003')
WITHIN_DAYS Boolean Date (which must be in the future) is within n working days of todays date
! Boolean Unary NOT
AND Boolean AND
OR Boolean OR
() any Bracketed subexpression

Dates for EARLIER_THAN, LATER_THAN and WITHIN_DAYS must be dates in the format expected by Time::ParseDate (like the ActionTrackerPlugin). WITHIN_DAYS works out the number of working days (i.e. excluding Saturday and Sunday). Apologies in advance if your weekend is offset ± a day! Integers will automatically be converted to dates, by assuming they represent a number of seconds since midnight GMT on 1st January 1970.

Example

Get a list of attachments that have a date earlier than 1st January 2000
  $db = new TWiki::Contrib::DBCacheContrib::DBCache( $web ); # always done
  $db->load();
  my $search = new TWiki::Contrib::DBCacheContrib::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";
       }
     }
  }

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

new($string)

  • $string - string containing an expression to parse
Construct a new search node by parsing the passed expression.

toString() -> string

Generates a string representation of the object.

--+++ =addOperator(%oper) Add an operator to the parser

%oper is a hash, containing the following fields:

  • name - operator string
  • prec - operator precedence, positive non-zero integer. Larger number => higher precedence.
  • arity - set to 1 if this operator is unary, 2 for binary. Arity 0 is legal, should you ever need it.
  • exec - the handler to implement the new operator

package TWiki::Contrib::DBCacheContrib::FileTime

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

read()

TWiki::Contrib::DBCacheContrib::Archive hook

package TWiki::Contrib::DBCacheContrib::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(".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::DBCacheContrib::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) -> search result

  • $search - TWiki::Contrib::DBCacheContrib::Search object to use in the search
Search the array for matches with the given object. values. Return a TWiki::Contrib::DBCacheContrib::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::DBCacheContrib::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::DBCacheContrib::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.

package TWiki::Contrib::DBCacheContrib::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.
  • get("[X]",$r) = will get the subfield named =X (so X[Y] and X.Y are synonymous)..
  • # means "reset to root". So get("#.Y", $r) will return the subfield =Y of $r (assuming $r is a map!), as will get("#[Y]".

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::DBCacheContrib::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) -> search result

  • $search - TWiki::Contrib::DBCacheContrib::Search object to use in the search
Search the map for keys that match with the given object. values. Return a TWiki::Contrib::DBCacheContrib::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::DBCacheContrib::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::DBCacheContrib::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.

Installation Instructions

{DBCache}{AlwaysUpdateCache}

If $TWiki::cfg{DBCache}{AlwaysUpdateCache} is set to FALSE (defaults to TRUE for compatibility) then DBCacheContrib will avoid calling _updateCache unless requested. _updateCache accesses every topic file in the web, so its an unnecessary performance hit. DBCacePlugin now only requests _updateCache from the afterSaveHandler and from the new REST updateCache handler.

You do not need to install anything in the browser to use this extension. The following instructions are for the administrator who installs the extension on the server where TWiki is running.

Like many other TWiki extensions, this module is shipped with a fully automatic installer script written using the BuildContrib.

  • If you have TWiki 4.2 or later, you can install from the configure interface (Go to Plugins->Find More Extensions)
  • If you have any problems, then you can still install manually from the command-line:
    1. Download one of the .zip or .tgz archives
    2. Unpack the archive in the root directory of your TWiki installation.
    3. Run the installer script ( perl <module>_installer )
    4. Run configure and enable the module, if it is a plugin.
    5. Repeat for any missing dependencies.
  • If you are still having problems, then instead of running the installer script:
    1. Make sure that the file permissions allow the webserver user to access all files.
    2. Check in any installed files that have existing ,v files in your existing install (take care not to lock the files when you check in)
    3. Manually edit LocalSite.cfg to set any configuration variables.

Contrib Info

Author: TWiki:Main.CrawfordCurrie
Copyright: This code is based on an original development of Motorola Inc. and is protected by the following copyrights:
© 2002-2003 Motorola Inc. All Rights Reserved.
Portions copyright © 2004. Crawford Currie http://www.c-dot.co.uk
© 2004-2011, TWiki:TWiki.TWikiContributor
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.
Version: 21578 (2011-07-07)
Change History:  
2011-07-07: TWikibug:Item6711: Small doc fix in Config.spec
2010-04-29: TWikibug:Item6433: Doc improvements
16347 remove META data from text hash; include META data in all hash. TWiki:Main/MichaelDaum
16346 caching all topic elements to an all field to allow th search in all of the text and the formfields like the normal grep-based SEARCH does. TWiki:Main/MichaelDaum
15868 fixed WITHIN_DAYS and EARLIER_THAN. TWiki:Main/MichaelDaum
15583 made query parser pluggable so that other plugins can implement their own predicates. TWiki:Main/MichaelDaum
15019 added {DBCache}{AlwaysUpdateCache} to remove the updateCache from every operation. TWiki:Main/SvenDowideit
13562 Bugs:Item3985 - fixed failures with hierarchical webs
13527 Moved the cache into the extensions work areas, instead of the web directory
12943 Bugs:Item3659: added automatic conversion of integers to dates
12923 added REF operator; added link to web object to hashes; fixed parent relation to end in WebHome; added "web" property to topic hashes; caching META:PREFERENCES now
11537 Added lc and uc operators for case-insensitive searches
9303 TWikibug:Item1844 - don't die on broken symlinks
8682 TWikibug:Item1580 - one-char fix that makes the difference
8110 TWikibug:Item663 - formatting and text fixes
7552 TWikibug:Item997 - test update
7274 TWikibug:Item719 - onReload() is not a static method.
7262 TWikibug:Item719 - MichaelDaum's patch (almost) to correct parameters to onReload
7260 TWikibug:Item727 - made it clean the form name using normaliseWebTopicName
6353 TWikibug:Item380 - do as the man says; make all $/ local
5720 Updated tests
5719 Fix for correct handling of parent relations
5229 Small improvement to the way it handles errors from Storable and Archive
5223 Documentation fixes, adding gifs.
5048 Cairo readiness
5036 Split from SharedCode
5031 Moving to new name
5030 About to rename
5019 Improved topic data model, cleaned up tests
5008 Added extended access syntax, [?], [*] etc.
5006 Doc fixes
5005 Poddified documentation
5003 Initial version
8 Jul 2004 Initial version, split out from FormQueryPlugin
Dependencies:
NameVersionDescription
Time::ParseDate>=2003.0211Required. Available from CPAN.
Storable>=2.07Recommended; 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
Appraisal: http://TWiki.org/cgi-bin/view/Plugins/DBCacheContribAppraisal

Related Topics: DBCachePlugin, DeveloperDocumentationCategory, AdminDocumentationCategory, TWikiPreferences

Topic attachments
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Topic revision: r35 - 2013-10-16 - PeterThoeny
 
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