%OnAddToSaveSet - what has changed

Question

Question

Jiri Svoboda · May 21, 2018

Hi community,

what is the best way to determine if a certain property got changed between %OpenId and %Save? Preferably in the %OnAddToSaveSet method.

Thanks,

Jiri

Discussion (7)0

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Robert Cemper · May 21, 2018

If you look for a dedicated Property You may use <propertyname>GetStored(id) to compare against the object in memory

e.g.

set id=22 set old=##class(Sample.Person).SSNGetStored(id)

so you bypass also the case when a value is written back finally unchanged (false modified)

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score 0 · Answer 1 · 2018-05-21T13:28:00-04:00

I know of i%PropName

where is m%PropName documented?

all I found is:

Internally, Caché also uses additional instance variables with names such as r%PropName and m%PropName,
but these are not supported for direct use.

And no hint how they could be used.

score 0 · Answer 2 · 2018-05-21T09:49:50-04:00

You can determine that in run time with:

$system.CLS.GetModified(oref) to ger if oref was modified
m%property to get if property changed

Here's a simple example of how it all works

 Class User.Person Extends (%Persistent)
{

Property Name As %String(DISPLAYNAME = "Name");

Property Age As %Integer(DISPLAYNAME = "Age");

/// Create one user
ClassMethod Recreate() As %Status
{
  do ..%KillExtent()
  set person = ..%New()
  set person.Age = $random(100)
  set person.Name = $random(100) 
  quit person.%Save()
}

/// do ##class(User.Person).Test()
ClassMethod Test()
{
  $$$QuitOnError(..Recreate())

  set person = ..%OpenId(1)
  do person.ModificationState()

  set person.Age = $random(100)
  do person.ModificationState()

  set person.Name = $random(100)
  do person.ModificationState()
}

/// Show current object state
Method ModificationState()
{
  write "Object modified: ", $system.CLS.GetModified(), !
  write "Name prop modified: ", ..IsNameModified(), !, !
}

/// Get name property modification status
Method IsNameModified() As %Boolean
{
  quit m%Name
}

}

Executing in terminal:

>do ##class(User.Person).Test()
Object modified: 0
Name prop modified: 0
 
Object modified: 1
Name prop modified: 0
 
Object modified: 1
Name prop modified: 1

Note that changing value back would still mark property as modified.

score 0 · Answer 3 · 2018-05-21T13:47:00-04:00

Eduard Lebedyuk May 21, 2018 to Robert Cemper

m%PropName returns 1 if the property value was modified, 0 if not.

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score 0 · Answer 4 · 2018-05-21T14:09:00-04:00

do you have any indication if this is just isModified()

or if new content is checked against old content

Reason: in past isModified () just checked write access, not the content.
So a change from TRUE to FALSE and back to TRUE between %OpenId() and %Save() was marked as change (false positive)

so this was finally dropped in favor of GetStored()

score 0 · Answer 5 · 2018-05-21T14:15:14-04:00

As I originally said

Note that changing value back would still mark property as modified.

Any change (except immediate same value) would set m%PropName to 1.

I think that checking m%PropName and only if it equals one additionally checking GetStored would work faster.

score 0 · Answer 6 · 2018-05-21T14:45:00-04:00

An interesting combination!

But (from Sample.Person):

zNameGetStored(id) public { Quit $Select(id'="":$listget($g(^Sample.PersonD(id)),2),1:"") }

there isn't that much to win.
If it then ends with %Save() it is kind of a prefetch of the global buffer.

I saw it mostly used instead of %Open() loading / swizzling the whole object in memory
if just 1 specific property was required.
(A kind of direct global access in disguise)