Derived settable attributes
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* Derived attributes use an OCL expression to calculate the presentation of another attribute.
* Derived attributes use an OCL expression to calculate the presentation of another attribute.


* Derived '''settable''' attributes use EAL to do the reverse, i.e. setting the source attribute from the entered value. The user input is in the vInputParameter variable.
* Derived '''settable''' attributes use EAL to do the reverse, i.e. setting the source attribute from the entered value. The user input is in the '''vInputParameter''' variable.
This opens up special handling of user input and "user shortcuts" in the UI. For example accepting only a number as a time entry.
This opens up special handling of user input and "user shortcuts" in the UI. For example accepting only a number as a time entry.



Revision as of 19:08, 17 September 2018

What is this?

  • Derived attributes use an OCL expression to calculate the presentation of another attribute.
  • Derived settable attributes use EAL to do the reverse, i.e. setting the source attribute from the entered value. The user input is in the vInputParameter variable.

This opens up special handling of user input and "user shortcuts" in the UI. For example accepting only a number as a time entry.

Example with Time (DateTime) and Decimal

This example uses FromTimeText, HoursText and ToTimeText for user input, but only FromTime and Hours for storing information in the database.

This special handling makes user input much simpler because it handles the users need to change any of the three values, updating the others behind the scenes.

TimeSpent class example.png

/Date is a derived attribute for easy access to a neighboring class' containing the date in DateTime format.

/EffectiveToTime is a derived attribute used a companion to the FromTime, again for symmetry in access the information.

Support function StringToTime()

To help the other function with conversion, a help function like this was created

if aText.length <= 2 then
  DateTime.Parse('1900-01-01 ' + aText + ':00')
else
  DateTime.Parse('1900-01-01 ' + aText)
endif

Note the addition of :00 to the text if it is short, this help the user out if entering just the hour part.

'1900-01-01' is an ugly hack to prevent storing the current date as part of the time entry. It would work anyhow, but this is slightly better.

Property inspector

Below is the property inspector setting for an derived settable attribute. Note the AttributeMode and then the Ocl and OclSet code.

DerivedSettable property inspector.png
/FromTimeText: String?

OCL

if self.FromTime.notNull then
  self.FromTime.formatDateTime('HH:mm')
else
  String.nullValue
endif

EAL (OclSet)

self.FromTime := self.StringToTime(vInputParameter)

/HoursText: String?

OCL

In Sweden we use comma, not the dot as a decimal separator. Hard coded replacement.

self.Hours.ToString('N2').Replace('.', ',')

EAL (OclSet)

Enable use of both comma and dot as decimal separator. Round to 2 decimals.

self.Hours := Decimal.Parse(vInputParameter.Replace(',', '.')).Round(2)

/ToTimeText: String?

The to-time is all calculated and only exist when showing and entering values.

OCL

if self.FromTime.notNull then
  self.FromTime.AddHours(self.Hours.Value.ToDouble).formatDateTime('HH:mm')
else
  String.nullValue
endif

EAL (OclSet)

Handle both setting Hours or FromTime based on what information is already present.

if self.FromTime.notNull then
  self.Hours := Decimal.Create(self.StringToTime(vInputParameter).Subtract(self.FromTime).TotalHours)
else
  self.FromTime := self.StringToTime(vInputParameter).AddHours(-self.Hours.ToDouble);
  0
endif
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