Why does powershell give different result in one-liner than two-liner when converting JSON?

user_7432 0
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Overview

From a powershell 3 prompt,, I want to call a RESTful service, get some JSON, and pretty-print it. I discovered that if I convert the data to a powershell object, and then convert the powershell object back to json, I get back a nice pretty-printed string. However, if I combine the two conversions into a one-liner with a pipe I will get a different result.

TL;DR: this:

PS> $psobj = $orig | ConvertFrom-JSON
PS> $psobj | ConvertTo-JSON

... gives me different result than this:

PS> $orig | ConvertFrom-JSON | ConvertTo-JSON

Original data

[
  {
    "Type": "1",
    "Name": "QA"
  },
  {
    "Type": "2",
    "Name": "whatver"
  }
]

Doing the conversion in two steps

I'm going to remove the whitespace (so it fits on one line...), convert it to a powershell object, and then convert it back to JSON. This works well, and gives me back the correct data:

PS> $orig = '[{"Type": "1","Name": "QA"},{"Type": "2","Name": "DEV"}]'
PS> $psobj = $orig | ConvertFrom-JSON
PS> $psobj | ConvertTo-JSON
[
    {
        "Type":  "1",
        "Name":  "QA"
    },
    {
        "Type":  "2",
        "Name":  "DEV"
    }
]

Combining the two steps with a pipe

However, if I combine those last two statements into a one-liner, I get a different result:

PS> $orig | ConvertFrom-JSON | ConvertTo-JSON
{
    "value":  [
                  {
                      "Type":  "1",
                      "Name":  "QA"
                  },
                  {
                      "Type":  "2",
                      "Name":  "DEV"
                  }
              ],
    "Count":  2
}

Notice the addition of the keys "value" and "Count". Why is there a difference? I'm sure it has something to do with the desire to return JSON object rather than a JSON array, but I don't understand why the way I do the conversion affects the end result.

powershell json
4 Answers

I've encountered the same problem here. I was able to resolve it by using a ForEach-Object and a PSCustomObject. Hope it helps you.

'' | ForEach-Object { [PSCustomObject]@{ prop= @( 1, 2 ) }} | ConvertTo-Json

It gives this, which is the expected behavior and using cleaner approach:

{
  "prop": [
        1,
        2
  ]
}
user_93032040
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