How to use 'previousRawValue' and 'previousBlockResults' in a Custom Tag History Aggregate function

Ignition
1

blockContext.previousRawValue and blockContext.previousBlockResults as described in the Custom Tag History Aggregates documentation are actually bound functions and must be utilized with parentheses to get the expected return value/object. Perhaps that is obvious to others but it took quite a bit of tinkering to figure that out and thought I’d share as there is very little mention of those in the forums.

Example Usage:

	print "blockContext.previousRawValue: {}".format(blockContext.previousRawValue) #  - QualifiedValue, the previous non-interpolated value received before this window
	print "blockContext.previousBlockResults: {}".format(blockContext.previousBlockResults) #  - QualifiedValue[], the results of the previous window.
	print "blockContext.previousRawValue(): {}".format(blockContext.previousRawValue()) #  - QualifiedValue, the previous non-interpolated value received before this window
	print "blockContext.previousBlockResults(): {}".format(blockContext.previousBlockResults()) #  - QualifiedValue[], the results of the previous window.

Results:

INFO   | jvm 2    | 2022/09/07 18:14:09 | blockContext.previousRawValue: bound method com.inductiveautomation.ignition.gateway.sqltags.history.query.processing.BlockContext.previousRawValue of {u'count': 1}
INFO   | jvm 2    | 2022/09/07 18:14:09 | blockContext.previousBlockResults: bound method com.inductiveautomation.ignition.gateway.sqltags.history.query.processing.BlockContext.previousBlockResults of {u'count': 1}
INFO   | jvm 2    | 2022/09/07 18:14:09 | blockContext.previousRawValue(): {v=43.54100036621094, q=Good, ts=Wed Sep 07 18:14:01 CDT 2022, intrp=false}
INFO   | jvm 2    | 2022/09/07 18:14:09 | blockContext.previousBlockResults(): array(com.inductiveautomation.ignition.common.model.values.QualifiedValue, [[-88, Good, Wed Sep 07 18:04:08 CDT 2022 (1662591848114)]])

@Colby.Clegg This is/was not clear in the documentation (to me), I suggest updating the documentation text and examples. I directed that comment at you solely because you provided the earliest reference to the documentation that I could find in the forums. Thanks.

Ignition v8.1.19

2

Specifically, the objects in question are a BlockContext and a QueryContext. We can definitely get the manual updated with more information.

1 Like
3

A few other items that I discovered with testing and are covered in the documentation but are easy to miss…

  • You can write your own key/value pairs to the blockContext dictionary and these persist across evaluation of samples within a given time window (block), blockContext is reset for each time window (block).
  • You can write your own key/value pairs to the queryContext dictionary and these persist across evaluation of remaining samples for all blocks (does not reset).
    Example Usage:
def print2log(qval, interpolated, finished, blockContext, queryContext):
	blockContextCount = int(blockContext.getOrDefault('count',0)) + 1
	blockContext['count'] = blockContextCount
	
	queryContextCount = int(queryContext.getOrDefault('count',0)) + 1
	queryContext['count'] = queryContextCount

	print '--- Query Sample: {} | Block ID: {} | Block Sample: {} ---'.format(queryContextCount, blockContext.blockId, blockContextCount)

	if finished:
		print '----------'
		return "Output to wrapper.log"

Results:

INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 1 | Block ID: 0 | Block Sample: 1 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 2 | Block ID: 0 | Block Sample: 2 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | ----------
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 3 | Block ID: 0 | Block Sample: 1 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 4 | Block ID: 0 | Block Sample: 2 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 5 | Block ID: 0 | Block Sample: 3 ---
...
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 53 | Block ID: 0 | Block Sample: 51 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 54 | Block ID: 0 | Block Sample: 52 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | ----------
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 55 | Block ID: 1 | Block Sample: 1 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 56 | Block ID: 1 | Block Sample: 2 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 57 | Block ID: 1 | Block Sample: 3 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 58 | Block ID: 1 | Block Sample: 4 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | ----------
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 59 | Block ID: 2 | Block Sample: 1 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 60 | Block ID: 2 | Block Sample: 2 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 61 | Block ID: 2 | Block Sample: 3 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 62 | Block ID: 2 | Block Sample: 4 ---
INFO   | jvm 2    | 2022/09/07 19:02:05 | ----------
INFO   | jvm 2    | 2022/09/07 19:02:05 | --- Query Sample: 63 | Block ID: 3 | Block Sample: 1 ---

@PGriffith I noticed that the Block ID of 0 (zero) is used for two different blocks, not sure if that is a bug. I’ll investigate further.

4

It's entirely possible it's a bug. As you may have noticed, this feature hasn't gotten much attention since it was first implemented.