The topic of for/while loop performance in Caché ObjectScript came up in discussion recently, and I'd like to share some thoughts/best practices with the rest of the community. While this is a basic topic in itself, it's easy to overlook the performance implications of otherwise-reasonable approaches.

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Pravin Barton · Mar 28, 2019 2m read
ObjectScript error handling snippets

ObjectScript has at least three ways of handling errors (status codes, exceptions, SQLCODE, etc.). Most of the system code uses statuses but exceptions are easier to handle for a number of reasons. Working with legacy code you spend some time translating between the different techniques. I use these snippets a lot for reference. Hopefully they're useful to others as well.

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Date range queries going too slow for you? SQL Performance got you down? I have one weird trick that might just help you out! (SQL Developers hate this!)*

If you have a class that records timestamps when the data is added, then that data will be in sequence with your IDKEY values - that is, TimeStamp1 < TimeStamp2 if and only if ID1 < ID2 for all IDs and TimeStamp values in table - then you can use this knowledge to increase performance for queries against TimeStamp ranges. Consider the following table:

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Robert Cemper · Jun 10, 2019 1m read
A more useFull Object Dump

During testing your code you are often confronted with the need to examine
the actual content of an object. Either using ZWRITE or $system.OBJ.Dump()
you get a picture of simple properties as "--- attribute values ---"
while "--- swizzled references ---" are more confusing than informative
and with "--- calculated references ---" you are just left in the lurch.

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Timothy Leavitt · Mar 17, 2021 3m read
Making the most of $Query

I ran into an interesting ObjectScript use case today with a general solution that I wanted to share.

Use case:

I have a JSON array (specifically, in my case, an array of issues from Jira) that I want to aggregate over a few fields - say, category, priority, and issue type. I then want to flatten the aggregates into a simple list with the total for each of the groups. Of course, for the aggregation, it makes sense to use a local array in the form:

agg(category, priority, type) = total

Such that for each record in the input array I can just:

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This article will describe and include an example of how to embed an external PDF file into an HL7 segment, specifically ADT_A01:2.3.1 OBX(). This can be useful when attempting to insert pictures or other external data into an HL7 message. In this example, the name of the PDF file to be embedded is provided in the incoming HL7 message in OBX(1):ObservationValue field.

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Cache tricks

Several years ago, long before Developer Community Portal was launched, I published a series of Caché tricks at one of Czech web sites. In this article, I’m posting translated version of one of them.

Capturing output of someone else’s methods or routines

Suppose you, or someone else created a useful method or routine, that was producing some computation that you’d like to benefit from, but the routine was writing output to process principal device.

You would like to use the data, but you need it not written to a device, but assigned to a variable. And, for any reason, you can’t modify the code. What can you do?

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Robert Cemper · Apr 25, 2020 2m read
Semi-Persistent Classes and Tables

If you define a Persistent Class / Table the class compiler generates for you an appropriate Storage definition.
A different option is to define a SQL mapping for an already existing Global storage. This has been excellently
explained already in a different series of articles. The Art of Mapping Globals to Classes 1 of 3

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What if you could serialize/deserialize objects in whatever format: JSON, XML, CSV,...; attending different criteria: export/import some properties and not others, transform values in this or that way before exporting/importing,...; and all of this without having to change the class definition? Wouldn't that be great??

Well, perhaps it's a goal too ambitious to reach 100% but, exploring this idea, I've developed a bunch of classes that I thought it was good to share. If you want to test, change, modify or improve the code, or just take a look at it, you can do it here. There you'll find a more detailed explanation (see

Be aware, this is a proof of concept for myself done in spare times, sure it's not robust enough or it can be done much better... but, I was just playing...ok, I could just wait to the new JSON Adaptor (coming soon!) that sure is going to resolve much more scenarios in a cleaner way, but... meanwhile... :-) ...

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A quine is a computer program which takes no input and produces a copy of its own source code as its only output.


How about a fun challenge?

The task is to write a quine in InterSystems ObjectScript. It can be a class, or a method, or a routine, or just a line to be executed in a terminal. You decide!

Here's some resources you might consider useful:

Hard mode: do not use source code access functions.

Here's my (extremely uninspired, I know) attempt:

Class User.Quine

/// do ##class(User.Quine).Test()
ClassMethod Test()
    set sc = ##class(%Compiler.UDL.TextServices).GetTextAsString($namespace, $classname(), .str)
    write str


It produces this output:

How many different ways of producing a quine are there in ObjectScript?

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Robert Cemper · Feb 8, 2021 3m read
WebSocket Client with embedded Python

This is a demo to make use of a simple WebSocket Client with Embedded Python in IRIS.

To continue my series of WebSocket Client I have added an example written in Python.
The most impressive experience was how easy the writing and testing of the client was
which happened total offline from IRIS.
Embedding, running and feeding the client with data from IRIS was also incredibly simple.

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DTL Transformations and GetValueAt/SetValueAt calls on HL7 messages will truncate any fields longer than 32K. To avoid this, the methods GetFieldStreamRaw and StoreFieldStreamRaw must be used when dealing with fields that might be larger than 32K. OBX:5 is a frequent example. These methods have some subtleties and must be used carefully.

This can't be done by simply dragging from left to right in a DTL. It must be done with a code action. Also, the StoreFieldStreamRaw call must be the last edit made to the segment because the segment becomes immutable after that.

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Lexi Hayden · Jul 18, 2017 2m read
Old/New Dynamic SQL Cheat Sheet

The newer dynamic SQL classes (%SQL.Statement and %StatementResult) perform better than %ResultSet, but I did not adopt them for some time because I had learned how to use %ResultSet. Finally, I made a cheat sheet, which I find useful when writing new code or rewriting old code. I thought other people might find it useful.

First, here is a somewhat more verbose adaptation of my cheat sheet:

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Timur Safin · Jul 18, 2016 15m read
Remote proxy objects via dynamic dispatch

This article created as side effect of preparations to the longer set of articles about simple, but still handy MapReduce implementation in Caché. I was looking for relatively easy way to pass arguments to (potentially) multiple targets via remote calling facilities. And after several attempts I have realized that we do have very powerful mechanism in the Caché ObjectScript which might be of particular help here – dynamic dispatch for methods and properties.

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A feature I recently used in working on ISC internal applications is the ability to send emails on behalf of someone. This is useful when generating system notifications from an application when you want some of them to show up as being from a specific person, perhaps posting comments on a work ticket.

In my case I was updating our facilities work order system for tracking requests. Normally all notification emails are sent from the same noreply email address. I wanted to change that so comments added from the original requester would show up as being from them and stand out.

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David Crawford · Jul 26, 2019 3m read
Dynamic SQL to Dynamic Object

Hello community! I have to work with queries using all kinds of methods like embedded sql and class queries. But my favorite is dynamic sql, simply because of how easy it is to manipulate them at runtime. The downside to writing a lot of these is the maintenance of the code and interacting with the output in a meaningful way.

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NOTE: This content was originally presented at the InterSystems Global Summit in 2014, however related topics often come up on the Developer Community so I have decided to turn this into an article for easier reference and discussion. However, much of the content was pulled directly from the presentation slides so the article format resembles that of a PPT deck more than paragraphs.

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Two fairly common requests we receive from HL7 customers are (1) how to remove all trailing delimiters for fields and segments in HL7 messages and (2) how to "find and replace" for an entire HL7 message (as opposed to one segment/field at a time). The code sample below shows a custom function that solves for item 1 and by extension item 2 above. In other words the same approach can be used for finding/replacing any sequence of chars in an entire HL7 message, with some tweaks to the custom function.

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