Manipulating a non-existent field

[elavy-harris]

I've written the following function to ensure that fields don't get created in the XML out of order:

function padField(field, padLength) {
	const fieldName = field.name();
	for (component = 1; component <= padLength; component++) {
		if (!field[fieldName + '.' + component].toString()) {
			field[fieldName + '.' + component] = '';
		}
	}
}

I call it with something like padField(msg['PV1']['PV1.7'], 9).

This works fine most of the time, but if there is no PV1.7 (e.g. PV1 only has the first 6 fields), it will fail on the name() call with the error TypeError: name is not a function, it is xml.

I can avoid the error by inserting if (!field.toString()) return;, but I really want to create all the components.

For the record, if I pass in a newly-created segment instead of a non-existent field, toString() is false, but name() works, i.e.

	let pv1 = createSegmentAfter('PV1',  msg['PID']);
	padField(pv1, 45);

Is there any way for this function to know how to do its job?

[rjkroll]

You could try something like this, which includes a check at the beginning to see if the field exists. If it doesn't, it creates the field and initializes the specified number of components. This ensures that the function can handle cases where the field is missing.

function padField(segment, fieldName, padLength) {
    if (!segment || typeof fieldName !== 'string' || !Number.isInteger(padLength) || padLength < 1) {
        throw new Error('Invalid input to padField function');
    }

    // Extract the field number from the fieldName (e.g., '7' from 'PV1.7')
    const fieldNumber = fieldName.split('.')[1];

    // Check if the field exists, if not, create it
    if (!segment[fieldName] || segment[fieldName].toString() === '') {
        segment[fieldName] = ''; // Initialize the field
    }

    // Pad the field with empty components
    for (let component = 1; component <= padLength; component++) {
        const componentKey = fieldName + '.' + component;
        if (segment[componentKey] == null || segment[componentKey] === '') {
            segment[componentKey] = '';
        }
    }

    return segment[fieldName];
}

usage: padField(msg['PV1'], 'PV1.7', 9); <--- or whatever segment

• Takes three parameters: the segment object, the field name, and the desired padding length.
• Works with any segment and field
• Creates the field if it doesn't exist.
• Pads the field with empty components up to the specified length.

[tonygermano]

I can see how this would address my issue. I was hoping there was a way to derive fieldName reliably, without having to specify it explicitly.

When you pass it a field which does not exist, you are passing in an empty XMLList, and as far as I can tell there is no way to retrieve the original call path that resulted in the empty XMLList. Not only can you not call the .name() method, but field.length() is zero (coincidentally, that's what you should have been using instead of !field.toString() for your early return) and field.parent() is undefined. When you pass it an existing field, then field.parent() should return the segment.

[tonygermano]

I'm guessing AI wrote the function at the top of this thread because it had a ton of mistakes that wouldn't have allowed it to work. This is a mostly working version of it. It also shows an alternative for checking if something exists in xml. Instead of segment[fieldName].length() > 0 you can also check fieldName in segment. Just be aware that the in operator has really low precedence, which is why I needed to wrap it in parenthesis to get the "not" value.

function padField(segment, fieldName, padLength) {
    if (!segment || typeof fieldName !== 'string' || !Number.isInteger(padLength) || padLength < 1) {
        throw new Error('Invalid input to padField function');
    }

    // Check if the field exists, if not, create it
    if (!(fieldName in segment)) {
        segment[fieldName] = <{fieldName}/>; // Initialize the field (but we aren't checking for correct order here!)
    }

    // Pad the field with empty components
    for (var component = 1; component <= padLength; component++) {
        var componentKey = fieldName + '.' + component;
        if (!(componentKey in segment[fieldName])) {
            segment[fieldName][componentKey] = <{componentKey}/>;
        }
    }

    return segment[fieldName];
}

[elavy-harris]

Thanks, @tonygermano .

The function I posted originally was fine for me, until I ran into the situation where the field didn't exist yet. Passing in fieldName, instead of deriving it, seems to be an adequate (although not elegant) solution. I'll look into using in or length() === 0 in place of toString().

field.parent() is undefined

I found your statement to be true, but somehow the object is aware of its parentage anyway. I did the following

padTest(msg['PID']['PID.99'], 3, 'PID.99');
logger.info('pid.99=' + msg['PID']['PID.99'].toString());

function padTest(field, padLength, fieldName) {
	logger.info('toString=' + field.toString() + ', length=' + field.length() + ', parent=' + field.parent());
	for (component = 1; component <= padLength; component++) {
		if (!field[fieldName + '.' + component].toString()) {
			field[fieldName + '.' + component] = '';
		}
	}
	logger.info('toString=' + field.toString() + ', length=' + field.length() + ', parent=' + field.parent());
}

This code populates PID.99 successfully, without any initialization, and the logger.info at the bottom of the function displays the contents of the PID segment.

While there's redundancy here (saying 'PID.99' twice), I think I prefer it in this case over passing in the parent and name. In addition to using the method for creating components in a field, I also use it for creating fields in a segment. That segment COULD be one of a repetition, so the parent is msg, but I might need to be referencing msg['PV1'][2].

[tonygermano]

Three main points -

1. I think the simplest solution is to use the code template I mentioned in my other answer.
2. You mentioned padding fields in a segment as well as components in a field. I think if you don't use option 1, then you should do this by default so that,
   • fields are created in the correct order, and
   • you don't need to worry about a field not existing when go to add components
3. You made an interesting discovery, but I don't know if that's how e4x is supposed to work or it's just a quirk of the current Rhino implementation. I personally would not rely on it, but it turns out you can get the fieldName without passing it in separately. I think something like this is closer to what you originally were trying to do.

function padTest(parent, padLength) {
    // create parent node if it does not exist in the current document
    if (parent.length() === 0) {
        parent.@temp = ''
        delete parent.@temp
    }

    const parentName = parent.localName()

    for (childId = 1; childId <= padLength; childId++) {
        var childName = parentName + '.' + childId
        if (!(childName in parent)) {
            parent[childName] = <{childName}/>;
        }
    }
}

However, this still has a problem that would be solved by using option 1. Presumably this could occur because you check if a child already exists before creating it. For example,

• Your newly created field, PID-99, already has components 1 and 3 defined.
• You call padTest(msg['PID']['PID.99'], 4)
• The field will create components 2 and 4 after the third component.

Finally, a minor point, I've been using parent[childName] = <{childName}/> instead of parent[childName] = ''. Both of them will replace existing child elements of the parent if they already exist or create a new child at the end of the list if not. The former will assign a truly empty element. The latter will assign a new element with a child text node containing an empty string. To illustrate,

js> var x = <xml/>
js> x.a = <a/>
js> x.b = ''
js> x.a['a.1'] = 'a.1'
a.1
js> x.b['b.1'] = 'b.1'
b.1
js> x.toString()
<xml><a><a.1>a.1</a.1></a><b><b.1>b.1</b.1></b></xml>
js> x.a.children().length()
1
js> x.b.children().length() // still contains the empty string text node
2

[elavy-harris]

@tonygermano For the question I was asking, I'm going to mark your prior comment as the answer, specifically for this chunk of code:

if (parent.length() === 0) {
  parent.@temp = ''
  delete parent.@temp
}

I had to modify it to use parent.temp instead of parent.@temp, because our linter doesn't like the "@". Since we've already determined that parent is empty, I don't think it matters what temp field we create and destroy.

I'll consider adopting your code template. For the record, I've got other use cases besides padField() that can also benefit from the "temp" logic, e.g. a function that processes provider fields so might be passed msg['PV1']['PV1.7'][i] or msg['PV1']['PV1.8'][i] or ....

Some questions, though:

1. What's the difference between name() and localName()? For my HL7 content, they both seem to return the same value.
2. Is there a significant difference between field.length()===0 and !field.toString()?
3. How did you get a command-line environment that would correspond with Mirth's Rhino?

Other comments:

1. I don't know how it works, but the E4X behavior I described seems essential. Really, there's no difference between msg['PID']['PID.99']['PID.99.1']='x' and let a=msg['PID']['PID.99'];a['PID.99.1']='x'. We know the former works as desired. Based on prior discussion, if we were to evaluate a in the middle of the latter, we'd find no apparent connection to msg['PID'].

[elavy-harris]

My linter also doesn't like <{childName}/>. Is new XML('<' + childName + '/>') equivalent?

[pacmano1]

Don't use your linter? (and what linter are you using?)

[elavy-harris]

Don't use your linter? (and what linter are you using?)

JAVASCRIPT_ES

[tonygermano]

This doesn't directly answer your question, but if you plan on adding fields out of order, I'd take a look at this code template. You can add fields or components in any order you want and have it clean up for you at the end of the transformer.

https://github.com/nextgenhealthcare/connect-examples/tree/master/Code%20Templates/Fix%20HL7%20Node%20Order