6 A workflow is a directed graph where the nodes are called "activities" and the
7 arcs are called "transitions".
9 - Activities define work that should be done within the OpenERP server, such as
10 changing the state of some records, or sending mails.
12 - Transitions control how the workflow will go from activities to activities.
14 When defining a workflow, one can attach conditions, signals, and triggers to
15 transitions, so that the behavior of the workflow can depend on user actions
16 (such as clicking on a button), changes to records, or arbitrary Python code.
21 Defining a workflow with data files is straightforward: a record "workflow" is
22 needed together with records for the activities and the transitions. For
23 instance here is a simple sequence of two activities defined in XML::
25 <record id="test_workflow" model="workflow">
26 <field name="name">test.workflow</field>
27 <field name="osv">test.workflow.model</field>
28 <field name="on_create">True</field>
31 <record id="activity_a" model="workflow.activity">
32 <field name="wkf_id" ref="test_workflow"/>
33 <field name="flow_start">True</field>
34 <field name="name">a</field>
35 <field name="kind">function</field>
36 <field name="action">print_a()</field>
38 <record id="activity_b" model="workflow.activity">
39 <field name="wkf_id" ref="test_workflow"/>
40 <field name="flow_stop">True</field>
41 <field name="name">b</field>
42 <field name="kind">function</field>
43 <field name="action">print_b()</field>
46 <record id="trans_a_b" model="workflow.transition">
47 <field name="act_from" ref="activity_a"/>
48 <field name="act_to" ref="activity_b"/>
51 A worfklow is always defined with respect to a particular model (the model is
52 given through the ``osv`` attribute on the ``workflow`` model). Methods
53 specified in the activities or transitions will be called on that model.
55 In the example code above, a workflow called "test_workflow" is created. It is
56 made up of two activies, named "a" and "b", and one transition, going from "a"
59 The first activity has its ``flow_start`` attribute set to True so that OpenERP
60 knows where to start the workflow when it is instanciated. Because
61 ``on_create`` is set to True on the workflow record, the workflow is
62 instanciated for each newly created record. (Otherwise, the workflow should be
63 created by other means, such as from some module Python code.)
65 When the workflow is instanciated, it will start by the "a" activity. That
66 activity is of kind ``function`` which means the action ``print_a()`` is a
67 method to be called on the ``test.workflow`` model (the usual ``cr, uid, ids,
68 context`` arguments are passed for you).
70 The transition between "a" and "b" does not specify any conditions. This means
71 the workflow instance will immediately progress from "a" to "b" (after "a" has
72 been processed), and thus also process the "b" activity.
77 Transitions provide the control structures to orchestrate a workflow. When an
78 activity is completed, the workflow engine will try to get across transitions
79 departing from the completed activity, towards the next activities. In their
80 simplest form they just link activities from one to the others (as in the
81 example above), and activities are processed as soon as the activities
82 preceding them are completed.
84 But instead of running all activities in one fell swoop, it is also possible to
85 block on transitions, going through them only when some criteria are met. Such
86 criteria are the conditions, the signals, and the triggers. They are detailed
92 When an activity has been completed, its outgoing transitions will be inspected
93 to see if it is possible for the workflow instance to proceed through them and
94 reach the next activities. When only a condition is defined (i.e. no signal or
95 trigger is defined), the condition is evaluated by OpenERP, and if it evaluates
96 to ``True``, the worklfow instance will go through.
98 By default, the ``condition`` attribute (i.e. the expression to be evaluated)
99 is just "True", which will trivially evaluate to ``True``.
101 Actually, the condition can be several lines long, and the value of the last
102 one will be used to test if the transition can be taken.
104 In the condition evaluation environment, several symbols are conveniently
107 - The database cursor (``cr``),
108 - the user ID (``uid``), the record ID tied to the workflow instance (``id``),
109 - the user ID wrapped in a list (``ids``),
110 - the model name (``model``),
111 - the model instance (``obj``),
112 - all the model column names,
113 - and all the record (the one obtained by browsing the provided ID) attributes.
118 In addition of a condition, a transition can specify a signal name. When such
119 signal name is present, the transition will not be taken directly (even if the
120 condition evaluates to true). Instead the transition will block, waiting to be
123 To wake up a transition with a defined signal name, the signal must be sent to
124 the workflow. A common way to send a signal is to use a button in the web
125 interface, using the ``<button/>`` element with the signal name as the ``name``
126 attribute of the button.
128 .. note:: The condition is still evaluated when the signal is sent to the
134 With conditions that evaluate to false, transitions are not taken (and thus the
135 activity it leads to will not be processed). Still, the workflow instance can
136 get new chances to progress across that transition by providing so-called
137 triggers. The idea is that when the condition fails, triggers are recorded in
138 database. Later, it is possible to wake-up specifically the workflow instances
139 that installed those triggers, offering them a new chance to evaluation their
140 transition conditions. This mechnism makes it cheaper to wake-up workflow
141 instances by targetting just a few of them (those that have installed the
142 triggers) instead of all of them.
144 Triggers are recorded in database as record IDs (together with the model name)
145 and refer to the workflow instance waiting for them. The transition definition
146 can thus provide a Python expression (using the ``trigger_model`` attribute)
147 that when evaluated will return the record IDs. Unlike the other expressions
148 defined on the workflow, this one is evaluated with respect to a model that can
149 be chosen on a per-transition basis with the ``trigger_expression`` attribute.
151 .. note:: Note that triggers are not re-installed whenever the transition is
157 While the transitions can be seen as the control structure of the workflows,
158 activities are the place where everything happen, from changing record states
161 Different kind of activities exist: ``Dummy``, ``Function``, ``Subflow``, and
162 ``Stop all``; different kind of activities can do different and they are
165 In addition to the activity kind, activies have some properties, detailed in
168 Flow start and flow stop
169 ''''''''''''''''''''''''
171 The ``flow_start`` attribute is a boolean value specifying if the activity
172 starts the workflow. Multiple activities can have the ``flow_start`` attribute
173 set to ``True`` and when instanciating a workflow for a record, OpenERP will
174 simply process all of them, and try all their outgoing transitions afterwards.
176 The ``flow_stop`` attribute is also a boolean value, specifying if the activity
177 ends the workflow. A workflow is considered to be completed when all its
178 activities with the ``flow_stop`` attribute set to ``True`` are completed.
180 It is important for OpenERP to know when a workflow instance is completed: a
181 workflow can have an activity that is actually another workflow (called a
182 subflow) and that activity will be completed only when the subflow is
188 An activity can embed a complete workflow, called a subflow (the embedding
189 workflow is called the parent workflow). The workflow to instanciate is
190 specified by the ``subflow_id`` attribute.
192 .. note:: In the GUI, that attribute can not be set unless the kind of the
193 activity is ``Subflow``.
195 The activity will be completed (and its outgoing transitions will be tried)
196 when the subflow is completed (see the ``flow_stop`` attribute above to read
197 about when a workflow is considered completed by OpenERP).
199 Sending a signal from a subflow
200 '''''''''''''''''''''''''''''''
202 When a workflow is used (as a sublfow) in the activity of a (parent) workflow,
203 the sublow can send a signal from its own activities to the parent by specifying a
204 signal name in the ``signal_send`` attribute. OpenERP will process those
205 activities normally and send to the parent workflow instance a signal with
206 ``signal_send`` value prefixed with ``subflow.``.
208 In other words, it is possible to react and take transitions in the parent
209 workflow as activities are executed in the sublow.