Calculations Module

This module was created by the the concept and business logic where develop for that scope but the rules are used in other context such as the















remove acceptance criteria form FS

cleaning FS specifics

move calculation rules in a specific table

add filter based on type and sub-type



The rules for the the calculation of the policy value or payment to HF can be complex and evolving. Therefore, the solution should bring flexibility, to avoid complete redesign and databases change when a parameter to define the contribution value is changed.
To bring that flexibility, the solution described here uses a Calculation Rule (the Calculation Rules are defined in additional openIMIS modules extending the Calculation Module). This module is defining a framework to design calculations and to manage their activation and versioning in openIMIS. This

The value of the parameters will be saved as a JSON string in the json_ext field.

Later, this module could be used as a framework to create event-based actions

Business process: example of the formal sector

This module will use a "generic contribution" to get the required parameters and the json_ext database field will be used to save the parameters (generic backend feature). Finally, a signal will trigger the calculation action. 

The left part, if there is no reachable technical solution will be hardcoded by having the contribution “knowing“ which are the related class (e.g CPB for PH insuree and contract detail and calculation for Contribution)



This module will rely heavily on the django signals

In order to have a generic approach that will make the code more readable, one argument will be expected in the signal, this argument will be called obj and should contain the instance of the class sending his signal:

my_signal= dispatch.Signal(providing_args=["instance","user"])

Use cases (specific to formal sector)

UC14-1: add a new Calculation rule (needs to change the openimis.json).
UC14-2: use the contribution_fe to select a calculation rule.
UC14-3: use the contribution_fe to display the parameters required by multiple calculation for an object.
UC14-4: replace a calculation rule.
UC14-5: remove a calculation rule.

Detailed design

Calculations Backend Module

Backend management code

The backend management code will be used to register the calculation sub-module parameters, the sub-module status and the ReadUpdate right management on the database.
This code should have a function to clean the table from the remove calculation
This code should manage the uniqueness of the active version for a given UUID

A Custom signal class be created to add a priority of calculation

from django.dispatch import Signal as BaseSignal from django.dispatch.dispatcher import _make_id class Signal(BaseSignal): def connect(self, receiver, sender=None, weak=True, dispatch_uid=None, priority=50): if dispatch_uid is None: dispatch_uid = _make_id(receiver) inner_uid = '{0}{1}'.format(priority, dispatch_uid) super(Signal, self).connect(receiver, sender=sender, weak=weak, dispatch_uid=inner_uid) self.receivers.sort()

Source of the sub Signal class:

absCalculationRule class

The calculation module will be composed of an abstract class "absCalculation" that will have those methods and members.
This class should be imported as a module in the subclass definition (inside the "hat" modules)


static version
The version is used to keep track of the changes in the version of the calculation rule,
integer inactive, future, active, archived
static UUID
UUID to follow the version of the calculation

static CalculationRuleName

short name of the calculation rule

static description

description text of the calculation

list of impacted class and parameters

<list>JSONObject objects {class:"className"(to be compare with property name of the FE details object which is pulled from BE), 'parameters':['type':"int",'name':"example",'label':{'en':'DiplayName'},'rights':{'read':"readAuthority", ‘write':"writeAuthority"},relevance:"frontendjsdisplaylogic",condition:"frontendjsvalidationlogic",'optionSet’:[]]} // list of the parameters required on other object,


relevance and condition are Nice to have.

Abstract Methods defined in rules







Methods defined in abstract class


return UUID


return version


return calculation rule name

get_rule_name(cls, sender, class_name, **kwargs):

return rule object is classname is part of impacted class


return description


return impacted_class_parameter


For object in listObject

if object.class == classname

return object

get_paramteres(ClassName, instance)

#className is the class name of the object where the calculation param need to be added

#instance is where the link with a calculation need to be found, like the CPB in case of PH insuree or Contract Details

This function has two steps

1- getRuleDetails(className)

2- define if the calculation should be used

for each “eligible“ ruleDetails,

checkCalculation(instance) #check if the calculation is really concerning the class for that context

return a list only with rule details that matches step 1 and 2

run_calculation_rules(instance, context)

this function will be register to the module signal via the ready function if the rule is active

1- getRuleDetails(instance.__class__)

2 if activeForObject(instance)


run_convert(instance, from, to, **argv)

execute the conversion for the instance with the first rule that provide the conversion (see get_convert_from_to)


get the possible conversion, return [calc UUID, from, to]

Module function/Service



this function will send a signal and the rules will reply if they have object matching the classname in their list of object

listruledetails = []

for all calculation rules (send signal):

if result_signal != []

merge listruledetails and result_signal

return listruledetails

calculate(instance, context)

for all calculation rules (send signal):

runCalculationRules(instance, context)

no return

get_parameters(ClassName, instance)

#className is the class name of the object where the calculation param need to be added

#instance is where the link with a calculation need to be found, like the CPB in case of PH insuree or Contract Details

listparameters = []

for all calculation rules (send signal):

if result_signal != []

merge listparameters and result_signal

return the ruleDetails that are valid to classname and related to instance

get_linked_class(List[ClassName] = None)

#List[ClassName] is send from FE, by checking the class used in page where the user ave access if None (in case too difficult to do on the FE) all liked class will be retrieve

for all calculation rules (send signal):

returnListClass = []

if listClass == None

sendsignal getLinkedClass(none)

if result_signal != []

merge returnListClass and result_signal


for class in listclasss

sendsignal getLinkedClass(class)

if result_signal != []

merge returnListClass and result_signal



return all the returnListClass


Calculation (prefix 153)

  • search → 153 001

  • update → 153 003 (to activate or not)

Calculations Frontend Module

(NICE TO HAVE, or via Django Admin)Calculation management page

This page will show the calculation page and change the status/activate a given version
This page should group the calculation by UUID


Standard contributions should be available for most of the entities (claims, contribution, contribution collection, policies, insuree ....)

  • PH insuree

  • Contract details

  • ContributionPlan

  • All the other are NICE TO HaVE

Those contributions should get the parameters template from the backend and display the relevant ones. The values should be saved in the JsonExt fields

Ideally the contribution from the main calculation module should manage the contribution form the rules in order to avoid having the same parameters twice. For example , a single insuree can have 2 contributions plan using those two rule different rules based on the income

I see two possible ways (one must be selected)

  • either by wrapping the fe contribution from the rules in a “overall calculation fe contribution“ (this will require rebuilding the front end when adding a rule)

  • by managing all the rule fe contributions directly within the calculation fe contributions using the parameters defined in the rules (preferred solution)

    • only simple type should be supported:

      • Number (int. float …)

      • Select ( choice list key(int)-> value([lang-strings]))

      • checkbox

    • refresh logic should be based on the link between the entity having the contribution and the entity that hold the calculation

    • Appearance/logic of the data should be defined based:

      • on the entity

      • on the rules related to this entity (directly or not)

    • (nice to have) format should be based on the rule fields constraint (regex)

    • (nice to have) constraint/ validation should be based on the rule fileds constraint (js test function)

    • Overall the logic use in enketo could be reused

Nice to have

Formula parser


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