How to compare JSON in powershell

Question

I have a requirement where I need to compare JSON object from a file to the JSON message which comes into Anypoint MQ queue. I am able to get the message from the queue. I have used below script but it is not working. I did both -eq and Compare-Object but they are not working.

$po_ps_output = $filemessagecontent | ConvertFrom-Json
$po_python_output = $mqmessagecontent.body | ConvertFrom-Json
$result = $po_ps_output -eq $po_python_output

Unanimity

Answer 1

If you just want to know if the two JSON-originated objects differ, without needing to know how:

$contentEqual = ($po_ps_output | ConvertTo-Json -Compress) -eq 
                ($po_python_output | ConvertTo-Json -Compress)

Note:

• ConvertTo-Json defaults to a serialization depth of 2 - use -Depth <n> if your data is more deeply nested to avoid truncation (potentiall data loss) - see this post.

• Converting back to JSON may seem like an unnecessary step, but the -Compress standardizes the output formatting to a single line with no extra whitespace, which ensures that incidental variations in formatting in the input (if you had used the input JSON text directly) are ignored.

---

If you want to know how the two JSON-originated objects differ:

Note: The following is only useful in the following, limited scenario - a generic, robust solution would require much more effort:

• The inputs have the same structure and differ only in property names / values.

• The ordering of (equivalent) properties is the same.

Compare-Object (($po_ps_output | ConvertTo-Json) -split '\r?\n') `
               (($po_python_output | ConvertTo-Json) -split '\r?\n')

The output will show the lines that differ, each representing a single property or primitive value; e.g.:

InputObject                   SideIndicator
-----------                   -------------
      "DOB":  "12-03-1994"    =>
      "DOB":  "12-03-1999"    <=

Note:

• => / <= indicate that the line is unique to the RHS / LHS.

• Again, the explicit reconversion to JSON is done to ensure uniform formatting; in this case, a line-oriented pretty-printed format that enables property-by-property comparison.

• Again, you may have to use -Depth to prevent truncation of data.

• For interactive inspection of differences, you can try a difference-visualization tool, such as the one built into Visual Studio Code, by passing the two JSON strings in pretty-printed form via files to
  code --diff <file1> <file2>.

---

As for what you tried:

ConvertFrom-Json creates [pscustomobject] instances, so you're comparing two instances of that type:

• If you use -eq, reference equality is tested for, because [pscustomobject] is a reference type and doesn't implement custom equality comparison.

  • Therefore, $po_ps_output -eq $po_python_output will only be $true if the two variables point to the very same object in memory - which is clearly not the case here, so you'll always get $false.

• If you use Compare-Object, the two instances are compared by their .ToString() values.

  • As of PowerShell Core 7.0.0-preview.4, regrettably, calling .ToString() on an instance of [pscustomobject] yields the empty string (''), which should be considered a bug - see this GitHub issue.

  • Therefore, Compare-Object $po_ps_output $po_python_output (unhelpfully) considers the two instances equal and returns nothing, since equal objects are by default not output (use -IncludeEqual to include them).

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