Computation Field API

Responsible for preforming the calculation.

ReportField Basic Structure:

Earlier in he docs you saw the computation fields '__total__quantity__' Let’s see how it’s written in slick_reporting.fields

from slick_reporting.fields import ComputationField
from slick_reporting.decorators import report_field_register


@report_field_register
class TotalQTYReportField(ComputationField):

    # The name to use when using this field in the generator
    name = '__total_quantity__'

    # the field we want to compute on
    calculation_field = 'quantity'

    # What method we want
    calculation_method = Sum  # the default

    # A verbose name
    verbose name = 'Total quantity'

If you want AVG to the field price then the ReportField would look like this

from django.db.models import Avg

@report_field_register
class TotalQTYReportField(ComputationField):

    name = '__avg_price__'
    calculation_field = 'price'
    calculation_method = Avg
    verbose name = 'Avg. Price'

How it works ?

The ReportGenerator is initialized with the needed configuration, it generates a list of the needed fields to be displayed and computed. For each computation field, it’s given the filters needed and asked to get all the results prepared. The preparation is a duty of the ReportField anyway, then for each report_model record, the ReportGenerator again asks each ComputationField to get the data it has for each record and map it where it belongs.

Bundled Report Fields

• __total__ : Sum of the field names value
• __total_quantity__ :Sum of the field names ‘quantity’
• __fb__ : Sum of the field value on the start date (or the start date of the active time series window)
• __balance__: Compound some of the field value .

Difference between total and balance is:

The field __total__ will return that client 1 bought 10 in Jan, 12 in Feb , 13 in March. while __balance__ will report client compound buy: 10 in Jan, 22 in Feb and 35 in March

Registering Report Field

To make this ReportField class available to the report, it has to be registered via report_field_register

Say you want to further customize your calculation, maybe you need to run a complex query

You can override both of those method and control the calculation

Calculation Flow:

ReportGenerator call

1. prepare
2. resolve

Two side calculation

# todo: # Document how a single field can be computed like a debit and credit.

ComputationField API

class slick_reporting.fields.ComputationField(plus_side_q=None, minus_side_q=None, report_model=None, queryset=None, calculation_field=None, calculation_method=None, date_field='', group_by=None, group_by_custom_querysets=None)

Computation field responsible for making the calculation unit

name = ''

The name to be used in the ReportGenerator

calculation_field = 'value'

the Field to compute on

calculation_method = <class 'django.db.models.aggregates.Sum'>

The computation Method

verbose_name = None

Verbose name to be used in front end when needed

requires = None

This can be a list of sibling classes, they will be asked to compute and their value would be available to you in the resolve method requires = [BasicCalculationA, BasicCalculationB]

type = 'number'

Just a string describing what this computation field return, usually passed to frontend

Below are some data passed by the ReportGenerator, for extra manipulation, you can change them

report_model = None

The model on which the computation would occur

group_by = None

plus_side_q = None

minus_side_q = None

You can customize those methods for maximum control where you can do pretty much whatever you want.

prepare(q_filters=None, kwargs_filters=None, queryset=None, **kwargs)

This is the first hook where you can customize the calculation away from the Django Query aggregation method This method et called with all available parameters , so you can prepare the results for the whole set and save it in a local cache (like self._cache) . The flow will later call the method resolve, giving you the id, for you to return it respective calculation

Parameters:

• q_filters –
• kwargs_filters –
• kwargs –

Returns:

resolve(current_obj, current_row=None)

Reponsible for getting the exact data from the prepared value :param cached: the returned data from prepare :param current_obj: he value of group by id :param current_row: the row in iteration :return: a solid number or value

get_dependency_value(current_obj, name=None)

Get the values of the ReportFields specified in requires

Parameters:

• current_obj – the current object which we want the calculation for
• name – Optional, the name of the specific dependency you want.

Returns:

a dict containing dependencies names as keys and their calculation as values or a specific value if name is specified.