Class | Ruote::Exp::CursorExpression |
In: |
lib/ruote/exp/fe_cursor.rb
|
Parent: | CommandedExpression |
This class implements the ‘cursor’ and the ‘repeat’ (loop) expressions.
The cursor expression is a kind of enhanced ‘sequence’. Like a sequence it will execute its child expression one by one, sequentially. Unlike a sequence though, it will obey ‘commands’.
cursor do author reviewer rewind :if => '${f:not_ok}' publisher end
In this simplistic example, the process will flow from author to reviewer and back until the reviewer sets the workitem field ‘not_ok’ to something else than the value ‘true’.
There are two ways to pass commands to a cursor either directly from the process definition with a cursor command expression, either via the workitem ‘command’ [special] field.
The commands that a cursor understands are listed here. The most powerful ones are ‘rewind’ and ‘jump’.
Rewinds the cursor up to its first child expression.
cursor do author reviewer rewind :if => '${f:not_ok}' publisher end
Whereas ‘rewind’ places the cursor back to the initial step with the current workitem, ‘reset’ will rewind it and start again but with the workitem as it was when it reached the cursor/repeat.
Exits the cursor.
cursor do author reviewer rewind :if => '${f:review} == fix' stop :if => '${f:review} == abort' publisher end
‘_break’ or ‘over’ can be used instead of ‘stop’.
Those two commands jump forth and back respectively. By default, they skip 1 child, but they accept a numeric parameter holding the number of children to skip.
cursor do author reviewer rewind :if => '${f:review} == fix' skip 2 :if => '${f:review} == publish' reviewer2 rewind :if => '${f:review} == fix' publisher end
Jump is probably the most powerful of the cursor commands. It allows to jump to a specified expression that is a direct child of the cursor.
cursor do author reviewer jump :to => 'author', :if => '${f:review} == fix' jump :to => 'publisher', :if => '${f:review} == publish' reviewer2 jump :to => 'author', :if => '${f:review} == fix' publisher end
Note that the :to accepts the name of an expression or the value of its :ref attribute or the value of its :tag attribute.
cursor do participant :ref => 'author' participant :ref => 'reviewer' jump :to => 'author', :if => '${f:review} == fix' participant :ref => 'publisher' end
It‘s OK to tag a cursor/repeat/loop with the :tag attribute and then point a command to it via :ref :
concurrence do cursor :tag => 'main' do author editor publisher end # meanwhile ... sequence do sponsor rewind :ref => 'main', :if => '${f:stop}' end end
This :ref technique may also be used with nested cursor/loop/iterator constructs :
cursor :tag => 'main' do cursor do author editor rewind :if => '${f:not_ok}' _break :ref => 'main', :if => '${f:abort_everything}' end head_of_edition rewind :if => '${f:not_ok}' publisher end
this example features two nested cursors. There is a "_break" in the inner cursor, but it will break the main ‘cursor’ (and thus break the whole review process).
The command expressions are merely setting the workitem field ‘command’ with an array value [ {command}, {arg} ].
For example,
jump :to => 'author' # is equivalent to set 'field:__command__' => 'author'
It is entirely OK to have a participant implementation that sets command by itself.
class Reviewer include Ruote::LocalParticipant def consume(workitem) # somehow review the book if review == 'bad' #workitem.fields['__command__'] = [ 'rewind' ] # old style workitem.command = 'rewind' # new style else # let it go end reply_to_engine(workitem) end def cancel(fei, flavour) # cancel if review is still going on... end end
This example uses the Ruote::Workitem#command= method which can be fed strings like ‘rewind’, ‘skip 2’, ‘jump to author’ or the equivalent arrays [ ‘rewind’ ], [ ‘skip’, 2 ], [ ‘jump’, ‘author’ ].
As an attribute of the cursor/repeat expression, you can set a :break_if. It tells the cursor (loop) if it has to break.
cursor :break_if => '${f:completed}' do participant 'alpha' participant 'bravo' participant 'charly' end
If alpha or bravo replies and the field ‘completed’ is set to true, this cursor will break.
:break_unless is accepted. :over_if and :over_unless are synonyms for :break_if and :break_unless respectively.
:rewind_if / :rewind_unless behave the same, but the cursor/loop, instead of breaking, is put back in its first step.
A ‘cursor’ expression exits implicitely as soon as its last child replies to it. a ‘repeat’ expression will apply (again) the first child after the last child replied. A ‘break’ cursor command might be necessary to exit the loop (or a cancel_process, but that exits the whole process instance).
sequence do repeat do author reviewer _break :if => '${f:review} == ok' end publisher end