In thinking about how to build web applications that scale, where
workitems get dispatched to people or groups, I found the stores
scheme to be a bit unwieldy. My thinking is as follows:
- Work items can be dispatched to a person.
- Work items can be dispatched to a group.
- I should not need to iterate over the work items in a store or all
relevant stores
looking at parameters in each work item to select workitems meant to
be acted
on by a user or group.. that's what databases are good at.
I've made a few slight extensions to the ActiveWorkItem that may be of
interest to people that have similar needs. The idea is that each
workitem, by convention has 'target' parameter.
e.g. consider a process for handling travel requests; where we have
defined the todo and approval stores to handle participants of the
form: todo.* and approval.* respectively.
A user creates a travel request. It must be approved by the person's
manager and
the person who holds the budget on which the travel will be re-
imbursed (may or may not be the same person). Then someone in our
travel group must fill in a form expected by our parent organization
(we are a laboratory at a university).
class Travel < OpenWFE::ProcessDefinition
set :v => "linemanager", :value => "approval_linemanager"
set :v => "budget", :value => "approval_budgetsupervisor"
set :v => "msuform", :value => "todo.msutravelform"
set :f => "recordid", :value => "#{$processInfo['recordid']}"
set :f => "requestor", :value => "#{$processInfo['requestor']}"
set :f => "type", :value => "#{$processInfo['type']}"
sequence do
concurrence do
linemanager :target =>
"user:#{$processInfo['linemanager']}"
budget :target =>
"user:#{$processInfo['budgetmanager']}"
end
msuform :target => "group:travel"
end
end
and where $processInfo is setup by the application to be a hash that
parameterizes the process instance. The modifications consist of
adding a key field to the ActiveRecordParticipant, target which is set
if the attribute['params'] hash has a key 'target'. showing these
changes:
class OwfeTables < ActiveRecord::Migration
def self.up
create_table :workitems do |t|
t.column :fei, :string
t.column :wfid, :string
t.column :wf_name, :string
t.column :wf_revision, :string
t.column :participant_name, :string
t.column :store_name, :string
t.column :dispatch_time, :timestamp
t.column :last_modified, :timestamp
t.column :target, :string #
<---- new field
end
add_index :workitems, :target, :unique => false # <---
an index
Making the target field an index should make these searches scalable
with
performance O(log(n)) where n is the number of in flight workitems for
most
decent database engines.
and this field gets set a bit later in the file in:
def Workitem.from_owfe_workitem (wi, store_name=nil)
i = nil
MUTEX.synchronize do
i = Workitem.new
i.fei = wi.fei.to_s
i.wfid = wi.fei.wfid
i.wf_name = wi.fei.workflow_definition_name
i.wf_revision = wi.fei.workflow_definition_revision
i.participant_name = wi.participant_name
i.dispatch_time = wi.dispatch_time
i.last_modified = nil
i.store_name = store_name
# If there is a target set that field as well...
<----- additions starts here.
if wi.attributes['params']
parameter_hash = wi.attributes['params']
if parameter_hash['target']
i.target = parameter_hash['target']
end
end
# <----- additions end here.
...
Now I can do things like fill the dashboard for a user by
@my_items =
Workitem.find_all_by_target("user:#{someusername}"}
and I can iterate over the groups the user is a member of doing
@my_items[thisgroup] =
Workitem.find_all_by_target("group:#{thisgroup}")
If it meets your needs, have fun with it... however the usual
disclaimers of merchantability and fitness apply ;-).
Ron.
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