How to Retrieve the Instrument Tag of a PI Point Using AF SDK: Understanding Lazy Loading

When working with OSIsoft PI and the Asset Framework (AF) SDK, it's common to need access to PI Point attributes, such as the Instrument Tag. However, new users may encounter a frustrating issue: the Instrument Tag appears in PI SMT (System Management Tools), but an attempt to access it via the AF SDK throws an error indicating that the attribute was not found.

Let's explore why this happens and how to resolve it.

The Challenge: Missing Instrument Tag in AF SDK

Suppose you're iterating over a list of PI Points and want to retrieve the Instrument Tag using code like this:

string instrumentTag = piPoint.GetAttribute(PICommonPointAttributes.InstrumentTag) as string;

Yet you receive an error or find the value is missing, even though PI SMT clearly shows the Instrument Tag is set.

The Solution: Explicitly Load Attributes

AF SDK employs a lazy loading strategy. This means that certain properties and attributes of objects, such as PI Points, are not fetched from the server until explicitly requested. This design pattern improves performance and responsiveness in client applications like PI System Explorer.

However, if you try to access an attribute that hasn't been loaded yet, you'll get an error. To remedy this, you should explicitly load the required attributes:

// Load the Instrument Tag attribute before accessing it
piPoint.LoadAttributes(PICommonPointAttributes.InstrumentTag);

string instrumentTag = piPoint.GetAttribute(PICommonPointAttributes.InstrumentTag) as string;

Why Lazy Loading?

Lazy loading optimizes network traffic and resource consumption. By default, AF SDK only fetches data from the PI Data Archive or AF Server when needed. This model is excellent for interactive applications but requires developers to be deliberate about preloading data.

Bulk Loading Strategies

When processing many PI Points, consider bulk loading to enhance performance. Rather than sequentially loading attributes for each point, you can use methods that retrieve attributes for multiple points at once, reducing the number of roundtrips to the server.

Takeaway

When accessing PI Point attributes like Instrument Tag via AF SDK, always remember to explicitly load those attributes before trying to use them. Understanding and leveraging lazy loading and bulk loading techniques will help your PI System applications perform efficiently and reliably.

Further Reading:

• AF SDK PI Point Attributes Documentation
• Best Practices for AF SDK Development