How to create a multi-level xml file using Powershell

Question

I planed to created config xml file for my small powershell application. To do this, I create an initialization procedure that polls the user and then generates a configuration file based on the data entered by him. The main program will take data from it, and not every time it starts. The procedure should create a file with something like this structure:

<CamInfoSettings>
  <Application>
    <AppFolder>C:\Temp\01</AppFolder>
    <PictureFolder>images</PictureFolder>
    <LogFiles>CamInfo.log</LogFiles>
  </Application>
  <Sections>
    <Count>1</Count>
    <Section id="1">
      <Name>FirstSection Name</Name>
      <Description>FirstSection Description</Description>
      <SectionNetworksCount>2</SectionNetworksCount>
      <FileName>C:\Temp\01\Section1.config</FileName>
      <SectionIpNetworks>
          <SectionIpNetwork id="1">
              <Network>192.168.12.</Network>
              <StartIp>22</StartIp>
              <FinishIp>99<FinishIp>
          <SectionIpNetwork id="2">
              <Network>192.168.13.</Network>
              <StartIp>1</StartIp>
              <FinishIp>254<FinishIp>
      </SectionIpNetworks>
    </Section>

I learned how to create xml using examples from this site, or from the Internet, but I got stuck on the part where I need to create several child elements in the SectionIpNetworks section. Since there are many networks that can be used with the main program, I would like to create a file with exactly this structure. I settled on the fact that I can create one or more networks, but I cannot assign them the "id" attribute and create children within each network.

I ask you to help with a small example. my procedure code asks the user for the number of networks, and then in a loop he must add items. Below is an example of code that creates branches, but further work stalled. Most likely I am making some kind of global mistake, which I have not been able to figure out for several days. My code:

$SectionEnumber = [int]$Configfile.CamInfoSettings.Sections.Count + 1
$Configfile.SelectSingleNode("CamInfoSettings/Sections/Count").InnerText = $SectionEnumber       
$newSectionNode = $Configfile.CamInfoSettings.Sections.AppendChild($Configfile.CreateElement("Section"))
$newSectionNode.SetAttribute("id",$SectionEnumber)
$newSectionName = $newSectionNode.AppendChild($Configfile.CreateElement("Name"))
$newSectionName.AppendChild($Configfile.CreateTextNode($SectionName)) | Out-Null
$newDescription = $newSectionNode.AppendChild($Configfile.CreateElement("Description"))
$newDescription.AppendChild($Configfile.CreateTextNode($SectionDescription)) | Out-Null
$newSegmentsCount = $newSectionNode.AppendChild($Configfile.CreateElement("SectionNetworksCount"))
$newSegmentsCount.AppendChild($Configfile.CreateTextNode($SectionNetworksCount)) | Out-Null
$newFileName = $newSectionNode.AppendChild($Configfile.CreateElement("FileName"))
$newFileName.AppendChild($Configfile.CreateTextNode($WritePath + "\" + "Section$SectionEnumber.config")) | Out-Null
$newSectionNode.AppendChild($Configfile.CreateElement("SectionNetworks")) | Out-Null
$newNetworksNode =  $Configfile.SelectSingleNode("CamInfoSettings/Sections/Section[@id=$SectionEnumber]/SectionNetworks")
$newNetworksNode.SetAttribute("count",$SectionNetworksCount)
foreach ($item in 1..$SectionNetworksCount) {
$newNetworksNode.AppendChild($Configfile.CreateElement("SectionNetwork")) |Out-Null

Here i must create Elements for SectionIpNetwork and set attruibute id=$item
}

"I planed to create a config xml file for my small powershell application" - might I suggest using JSON as a config file format instead? JSON would be much easier to build and much easier to maintain. — Tomalak
– Tomalak, Commented Oct 17, 2021 at 15:11
my main application will use api requests for equipment, and they all return in xml, which is why I wanted to use xml. certainly there is no difference in what format the config file will be, and whether it has a structure. But if I left the structure as described above, it would be more readable. — Владимир Костяник
– Владимир Костяник, Commented Oct 17, 2021 at 15:43
"More readable" compared to what? (You need to think of your code's readability, too, and that's already off to a bad start.) — Tomalak
– Tomalak, Commented Oct 17, 2021 at 15:49

Tomalak · Accepted Answer · 2021-10-17 16:20:04Z

2

I think you are in for a lot of hurt when you try to keep XML as your config format. I recommend switching to JSON.

This is the equivalent of your config structure.

{
    "Application": {
        "AppFolder": "C:\\Temp\\01",
        "PictureFolder": "images",
        "LogFiles": "CamInfo.log"
    },
    "Sections": [{
        "id": 1,
        "Name": "FirstSection Name",
        "Description": "FirstSection Description",
        "FileName": "C:\\Temp\\01\\Section1.config",
        "SectionIpNetworks": [{
                "id": 1,
                "Network": "192.168.12.",
                "StartIp": 22,
                "FinishIp": 99
            },
            {
                "id": 2,
                "Network": "192.168.13.",
                "StartIp": 1,
                "FinishIp": 254
            }
        ]
    }]
}

Reading it is straightforward:

$config = Get-Content config.json -Raw -Encoding UTF8 | ConvertFrom-Json

Accessing it is straightforward⁽¹⁾:

$appFolder = $config.Application.AppFolder

$section = $config.Sections | Where id -eq 1

Changing it is straightforward⁽²⁾:

# adding an array entry
$section.SectionIpNetworks += [pscustomobject]@{
    id = 3
    Network = "192.168.14."
    StartIp = 1
    FinishIp = 254
}

# removing an array entry
$section.SectionIpNetworks = $section.SectionIpNetworks | Where id -ne 1

Writing it is straightforward⁽³⁾:

$config | ConvertTo-Json -Depth 10 | Set-Content config.json -Encoding UTF8

⁽¹⁾ That part actually works exactly the same for both XML and JSON in this case.

⁽²⁾ The cast from PowerShell hash (@{}) to [pscustomobject] is necessary here. But you can see how easily native PowerShell data structures convert to JSON.

⁽³⁾ The -Depth parameter is important. Also, PowerShell has a slightly unconventional idea of how to format JSON, but it's manageable.

As a general tip: Don't store self-evident things as config options. You don't need a value storing the section count or the network count. If you need to know how many there are, count them:

$numSections = $config.Sections.Length

Storing these things only leads to bugs once they get out of sync with reality for whatever reason.

edited Oct 17, 2021 at 16:20

answered Oct 17, 2021 at 15:40

Tomalak

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4 Comments

Владимир Костяник Over a year ago

I think you are right, i reorganize my config to JSON.

Tomalak Over a year ago

@ВладимирКостяник There is one small cotcha that you need to be aware of - it's not straightforward to add new keys to an object. When you have $test = '{"a": 1}' | ConvertFrom-Json , trying $test.b = 2, will fail with a "The property 'b' cannot be found on this object." error. Use $test | Add-Member NoteProperty -Name "b" -Value 2 for this. (Then again, config files tend to have a predefined, fixed structure - you should not often need to add new properties dynamically.)

Владимир Костяник Over a year ago

Thank you, @Tomalak! Your advice is really cool. My code for xml contain 20 string, for JSON - 5. Thank you

Tomalak Over a year ago

@ВладимирКостяник You're welcome! Glad to hear it worked out so well!

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