How to efficiently store historical data, similar to current data, without mixing physical storage ?
Let's consider you would like to efficiently store your historical data in a similar structure than the one used for your current data, but without sharing the same physical storage (ie : not in the same global). What is the most efficient way to do it ?
Below a simple class of your current data :
Class data.current.person Extends (%Persistent, %Populate) { Parameter DEFAULTGLOBAL = "^on.person"; Property name As %String; Property dob As %Date(FORMAT = 4); Property activ As %Boolean [ InitialExpression = 1 ]; Property created As %TimeStamp [ InitialExpression = {$zdt($h,3)} ];
Storage Default { <Data name="personDefaultData"> <Value name="1"> <Value>%%CLASSNAME</Value> </Value> <Value name="2"> <Value>name</Value> </Value> <Value name="3"> <Value>dob</Value> </Value> <Value name="4"> <Value>activ</Value> </Value> <Value name="5"> <Value>created</Value> </Value> </Data> <DataLocation>^on.personD</DataLocation> <DefaultData>personDefaultData</DefaultData> <IdLocation>^on.personD</IdLocation> <IndexLocation>^on.personI</IndexLocation> <StreamLocation>^on.personS</StreamLocation> <Type>%Storage.Persistent</Type> } }
NB : you can omit the DEFAULTGLOBAL parameter if you're happy with the one automatically generated (which is the case, most of the time) ; I use it in my example to emphasize the separation of globals in current and archive classes.
First approach
You could first think about creating 2 persistent classes and copy the same definition in both classes (except the Storage clause which will be recreated at the first compilation) :
Class data.current.person Extends %Persistent {}
Class data.archive.person Extends %Persistent {}
But this approach will rapidly reveal itself disastrous in terms of maintenance, for obvious reason of duplicating the code/definitions.
Second approach
Another idea could be to create a common class with ClassType = "" in order to not create the storage definition at its level. Then, you can make archive and current classes inherit from this common class and add %Persistent inheritance in both subclasses.
Class data.common.person Extends %Persistent [ ClassType = "" ] {}
Class data.current.person Extends (%Persistent,data.common.person) [ClassType = persistent ] {}
Class data.archive.person Extends (%Persistent,data.common.person) [ ClassType = persistent ] {}
This way, you solve the question and get separate globals for each persistent class with a unique class to store all the definition.
But, this is not really convenient to manage 3 classes instead of 2 and to have to maintain the definition in the common class ; neither to be obliged to open the common class to get the detail of the definition of the current class.
Third approach
Well, a third solution could be to return to a very simple approach : just create an archive class which inherits from the current data class...
Class data.current.person Extends %Persistent {}
Class data.archive.person Extends data.current.person {}
In that case, current and historical data will share the same storage definition and, as a result, their data will be stored in the same globals, which is not really convenient to physically separate both kind of data and thus not answering to our need.
A simpler approach
You can obtain a similar structure in archive class which inherits from current, without inheriting from its storage, by simply adding %Persistent inheritance before the class you want to inherit from.
In this case, even if the super class already contains a storage class with DataLocation (because of its persistent type), at compile time, the inheritance precedence will force the generation of a new storage clause based on the subclass definition, with its own storage for DataLocation, IdLocation, IndexLocation, StreamLocation.
Class data.archive.person Extends (%Persistent, data.current.person) { Parameter DEFAULTGLOBAL = "^off.person";
Storage Default { <Data name="personDefaultData"> <Value name="1"> <Value>%%CLASSNAME</Value> </Value> <Value name="2"> <Value>name</Value> </Value> <Value name="3"> <Value>dob</Value> </Value> <Value name="4"> <Value>activ</Value> </Value> <Value name="5"> <Value>created</Value> </Value> </Data> <DataLocation>^off.personD</DataLocation> <DefaultData>personDefaultData</DefaultData> <IdLocation>^off.personD</IdLocation> <IndexLocation>^off.personI</IndexLocation> <StreamLocation>^off.personS</StreamLocation> <Type>%Storage.Persistent</Type> } }
Other ideas ?
If you have other ways to address this question, please share your ideas and comments.
You can find the full definitions of current and archive classes on Github.
I'm using a modified second approach.
1. Create a base abstract class with all properties:
2. Create persistent class:
Utils.Copyable allows easy copy/compare.
3. Create snapshot class:
And done.
This way you can add a snapshot of object at any point of time and by calling compareTo calculate a diff between any two versions.
There's also a hash function you can use to calculate hash from some or all object properties to speed up equivalence checks.
Thanks Eduard for sharing your code implementing a very powerful approach of data snapshot.
You have a lucky design without indices. That makes life with 2 distinct globals easy.
The archiving action maintaining the original ID could be achieved by a simple
MERGE from ^source to ^archive. maintenance of indices could be slightly
effort requiring class methods.
Thanks Robert for your comment.
Merging globals is exactly what the toArchive method does here :
Okay, why would you want to index active versions and old versions together?
In my design I explicitly create indices for the active version only. Old versions are only indexed on the parent field.
Why together ? ? ? Who wants that ? ? ? Where ? ? ?
A simple MERGE ^archive(....)=^source(....) just doesn't maintain any index.
this was my message
I though you have a common index for current and archive versions. I guess I misunderstood your point.
I think the biggest issue is that it can store only one (previous) version. Or if you merge:
you'll need a custom storage for a composite id key.
YEAH! A history track makes it definitely more complex
Social networks
InterSystems resources
Log in or sign up
Log in or create a new account to continue
Log in or sign up
Log in or create a new account to continue
Log in or sign up
Log in or create a new account to continue