# Sending Datasets through Messages

**URL:** <https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188>\
**Category:** Ignition\
**Created:** [November 17, 2021, 3:22pm UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188 "2021-11-17T15:22:51Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![bradbarbin](https://avatars.discourse-cdn.com/v4/letter/b/ee59a6/32.png) [@bradbarbin](https://forum.inductiveautomation.com/u/bradbarbin)\
**Post date:** [November 17, 2021, 3:22pm UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188/1 "2021-11-17T15:22:51Z")

</div>

I’m using `system.util.sendRequest` to call functionality in one project (call it A) from another (call it B) and running into some strange behavior. Would appreciate some advice.

In project B, I have some code like this:

```python
def GetSomething(id):
	payload = {
		'id': id,
	}
	
	result = system.util.sendRequest(
		project='A', 
		messageHandler='GetSomething',
		payload=payload, 
		remoteServer=ENTERPRISE_SERVER
	)
									
	return result

```

In project B, I have code like this:

```python
def GetSomething(id):
	
	try:
		namedQuery = 'GetSomething'
		data = system.db.runNamedQuery(namedQuery, {'id': id})
		return data
	except:
		return system.dataset.toDataSet([],[])

```

This works, which tells me that the message handler is configured correctly.

**HOWEVER** , when I try to send return a `dict` that contains the dataset, I get a bunch of weird behavior (connection timeouts). This is basically what causes the errors:

```python
def GetSomething(id):
	
	try:
		namedQuery = 'GetSomething'
		data = system.db.runNamedQuery(namedQuery, {'id': id})
		return {
			'error': False,
			'data': data
		}
	except:
		return {
			'error': True,
			'message': 'Descriptive error message'
		}

```

What’s going on here? I know I can send `dict`s through messages. Why can’t I send a `dict` with a dataset as a value through a message? Am I missing something?

---

<div class="post-metadata">

**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [November 17, 2021, 3:55pm UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188/2 "2021-11-17T15:55:49Z")

</div>

It’s a bug.

If you wrap your dataset in a BasicDataset by importing  
`com.inductiveautomation.ignition.common.BasicDataset`, then construct it from your `runNamedQuery` return object:  
`'data': BasicDataset(data)`  
It should send over the wire okay.

I believe this bug is on track to be fixed in 8.1.13 or so.

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [November 18, 2021, 12:14am UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188/5 "2021-11-18T00:14:23Z")

</div>

Python dictionaries explicitly disclaim any ordering of keys. Makes it very hard to truly “restore” a dataset from a dictionary. Just wrap in the BasicDataset. It serializes very efficiently.

---

<div class="post-metadata">

**Author:** ![bradbarbin](https://avatars.discourse-cdn.com/v4/letter/b/ee59a6/32.png) [@bradbarbin](https://forum.inductiveautomation.com/u/bradbarbin)\
**Post date:** [November 18, 2021, 8:50pm UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188/6 "2021-11-18T20:50:41Z")

</div>

Thanks guys.

@pturmel not sure what you mean by “explicitly disclaim order of keys”, but I think I see what you’re getting at with in that an decoded-and-then-encoded dataset wouldn’t always have the same ordering of rows or columns. It’s a good point.

I agree that the `BasicDataset` wrapper solves the problem. But I’m also glad to have discovered some helper methods in the process. Personally, I’m from the JSON data school. And I really like the ability to be able to work with datasets like this:

```auto
results = ConvertDatasetToListOfDicts(dataset)
for row in results:
    row['NEWCOLUMN'] = row['COLUMNNAME'] + 5
dataset = ConvertListOfDictsToDataset(results)

```

And for anyone who wants to turn python datasets into a `list` of `dict`'s (like JSON), here some utility methods for that:

```python
def ConvertDatasetToListOfDicts(dataset):
	data = system.dataset.toPyDataSet(dataset)
	return [
		{
			colName: value
			for colName, value in zip(data.columnNames, list(row))
		} for i, row in enumerate(data) 
	]	    

def ConvertListOfDictsToDataset(data):
	# assumes the dicts are only one level deep (i.e. no nested dicts)
	# assumes that data is similarly shaped in each object
	
	headers = []
	rows = []
	
	if len(data) != 0:
		prototype = data[0]
		for key in prototype:
			headers.append(key)
		
		for row in data:
			values = []
			for column in headers:
				values.append(row[column])			
			rows.append(values)
	
	return system.dataset.toDataSet(headers,rows)

```

Hope someone is able to get some use out of that code. Thanks again for the workaround guys!

---

<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [November 18, 2021, 9:03pm UTC](https://forum.inductiveautomation.com/t/sending-datasets-through-messages/53188/7 "2021-11-18T21:03:13Z")

</div>

> [@bradbarbin](#):
>
> not sure what you mean by “explicitly disclaim order of keys”

Python's (and Jython's) docs point out that dictionaries are implemented with hash tables that do not retain the order that key/value pairs were inserted. You get back whatever key order the hash table implementation pleases. The only guarantee is that the order of keys and values will correspond if there hasn't been any changes between accesses.