Hi, Today, I got a talk with Nicolas about the relevance of the workflow engine in Tryton. We came to the conclusion that it will be perhaps better to drop it. So here are the arguments:
- The Subflow which is indeed a key feature in the design of workflow is
never used in Tryton because by experience (on OpenERP) we knew that
it doesn't allow enough flexibillity. Most of the time, you need to
trigger the workflow in some other activities then the starting/ending
one.
- The flexibility. Normally the workflow engine must provide
flexibility but in the reallity, we have most of the time more
difficulty to modify it through modules (any standard module does it).
So we manage it by inheriting some methods.
- Simplicity. Just looking at the workflow of sale and you understand
that when you try to modelise complet life cycle of a document, the
workflow becomes very complex. But we can print a picture of it.
- Misunderstanding, most of the developpers (and users) think that the
workflow is linked to the status of the document but because of the
nature of the engine, it is not. And you can have inconsistency
between both.
- Speed, it is well know that the workflow engine is not very fast. Does
it deserve this sacrifice?
- Security, this is a point where it is good. The access right to go
througth a transition works well.
So by what could we replace the workflow engine?
The idea will be to have just simple method calls. Those methods will
replace the activities. The transitions will be replaced by different
way:
- buttons which are linked to methods
- methods that call other methods
- triggers? (not sure because they can be heavy)
The security will be replaced by capacities. So some method will be able
to check (via decorator?) if the user has a specific capacity to run the
method. The capacities will be defined in XML and they will be linked to
groups.
The workflow trigger will be replaced by overriding the right method of
the target model (it is already done like that with model without
workflow).
Optional advantage of such design is the traceback of calls will be more
clear.
So what do you think?
--
Cédric Krier
B2CK SPRL
Rue de Rotterdam, 4
4000 Liège
Belgium
Tel: +32 472 54 46 59
Email/Jabber: cedric.kr...@b2ck.com
Website: http://www.b2ck.com/
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