Robert Cemper · Apr 27, 2020 4m read

Multidimensional Property Persistence - Part 1 (Classic)

As you know in Caché / IRIS you have the possibility to define a property as Multidimensional as documented here:
and the explanation of how to use it

Though the access is quite comfortable (in traditional COS sense) there are 2 main restrictions that hurt:

#1) It is not saved to disk unless your application includes code to save it specifically.
#2) It cannot be stored in or exposed through SQL tables
   there are some more
I'll show how to overcome these limits

#1)  Let's take this simple class as example:

Class DC.Multi Extends (%Persistent, %Populate) [ Final ]
    Property Name As %String;
    Property DOB As %Date;
    Property Multi As %String [ MultiDimensional 
] ;

The storage map already shows issue #1 no place for "Multi"

Storage Default
  <Data name="MultiDefaultData">
    <Value name="1">
    <Value name="2">

so we add 2 Methods:

/// save Multidimensional property
Method %OnAfterSave(insert As %Boolean) As %Status [ Private, ServerOnly = 1 ]
{    Merge ^(..%Id(),"Multi")=i%Multi quit $$$OK   }

/// load Multidimensional property
Method %OnOpen() As %Status [ Private, ServerOnly = 1 ]
{   Merge i%Multi=^(..%Id(),"Multi") quit $$$OK  }

we just attach the orphaned structure to our actual object.

To be honest:
This is not my invention, but the (simplified) approach that was used
in class %CSP.Session when it was written around the start of the millennium.


With the next simple add-on your multidimensional structure becomes persistent.

The object in memory looks like this:

CACHE>zw o2
o2=3@DC.Multi  ; <OREF>
+----------------- general information ---------------
|      oref value: 3
|      class name: DC.Multi
|           %%OID: $lb("2","DC.Multi")
| reference count: 2
+----------------- attribute values ------------------
|       %Concurrency = 1  <Set>
|                DOB = 62459
|         Multi("a") = 1
|     Multi("rob",1) = "rcc"
|     Multi("rob",2) = 2222
|               Name = "Klingman,Uma C."

and that's the related storage, a nice multidimensional global:

CACHE>zw ^DC.MultiD(2)
^DC.MultiD(2)=$lb("Klingman,Uma C.",62459)

OK so far:

#2) SELECT * from DC.Multi
has no idea what a column "Multi" might be.

so we add an SQLfriedly calculated property and some appropriate styling.

Property SqlMulti As %String(MAXLEN = "") [ Calculated, SqlComputed,
= { set {*}= ##class(DC.Multi).ShowMulti({ID}) } ];
ClassMethod ShowMulti(id) As %String(MAXLEN="")
{  set res="{"
   if $isobject(obj) {
      set qry=$query(obj.Multi(""),1,value)
      while qry'="" {
         set res=res_$piece(qry,".",2,99)_"="_value_","
     set $extract(res,*)=""
   quit res_"}"   

And it looks like this

No need to say that the design is totally in your hands.

As there is evident progress from the past the next article will show
you a solution more appropriate to the new century.


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