Question 286771 in Json Question posted in
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ms powershell: how to handle json- objects?

I have a file with content

{
  "Names" : {"first" : "Chuck", "second" : "Norris"},
  "Numbers" : {"one" : "1", "two" : "2"}
}

I can read/write and convert it with ConvertFrom-Json and ConvertTo-Json, this is no problem. And I can change f.e. "Chuck" into "Carlos Ray".
But how can I

  • add a new tuple like f.e. Months ("1st" : "January" …)
  • add a row inside an existing tuple, f.e. "Numbers" -> "three" : 3
  • delete a row
  • delete a tuple

? That means: I want to read the file and convert it into $variable, modify the $variable and convert and write the file.

Thank you very much

Tags:

2

Answers


  1. 0 
    $json = @'
{
  "Names" : {"first" : "Chuck", "second" : "Norris"},
  "Numbers" : {"one" : "1", "two" : "2"}
}
'@ | ConvertFrom-Json

    Add a new tuple like f.e. Months ("1st" : "January" …)

    $json.PSObject.Properties.Add(
    [psnoteproperty]::new(
        'Months',
        [pscustomobject]@{ '1st' = 'January' }))
$json | ConvertTo-Json

    Add a row inside an existing tuple, f.e. "Numbers" -> "three" : 3

    $json.Numbers.PSObject.Properties.Add(
    [psnoteproperty]::new('three', '3'))
$json | ConvertTo-Json

    Delete a row

    Removing the added Months property from 1st example.

    $json.PSObject.Properties.Remove('Months')
$json | ConvertTo-Json

    Delete a tuple

    Removing the added three object.

    $json.Numbers.PSObject.Properties.Remove('three')
$json | ConvertTo-Json
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  2. 0

    To complement Santiago Squarzon’s helpful answer:

    ConvertFrom-Json is PowerShell’s cmdlet for parsing JSON text into object graphs.

    • In Windows PowerShell, you invariably get [pscustomobject] graphs, and Santiago’s answer shows you how to work with those.

    • In PowerShell (Core) 7+, you have the option to get (ordered) [hashtable] graphs, using the -AsHashTable switch.

    Hashtable-based object graphs are generally lighter-weight and better suited to later modification, such as in your case:

    # PS 7+ ONLY
$fromJson = @'
{
  "Names" : {"first" : "Chuck", "second" : "Norris"},
  "Numbers" : {"one" : "1", "two" : "2"}
}
'@ | ConvertFrom-Json -AsHashtable

# --- UDPATE / ADDITION operations

# Update a nested entry.
$fromJson.Names.first = 'Carlos Ray'

# Add a new top-level entry
$fromJson.Months = [ordered] @{ '1st' = 'January'}

# Add a new nested entry
$fromJson.Numbers.three = 3

# Print the state of the hahstable now.
$fromJson | Out-Host

# --- REMOVAL operations

# Remove a top-level entry
$fromJson.Remove('Names')

# Remove a nested entry
$fromJson.Numbers.Remove('two')

$fromJson | Out-Host

    Output:

    # After entry updates / additions.
Name                           Value
----                           -----
Names                          {[first, Carlos Ray], [second, Norris]}
Numbers                        {[one, 1], [two, 2], [three, 3]}
Months                         {[1st, January]}


# After entry removals.
Name                           Value
----                           -----
Numbers                        {[one, 1], [three, 3]}
Months                         {[1st, January]}

    Note:

    • In PowerShell 7.3+, -AsHashtable returns a graph of [System.Management.Automation.OrderedHashtable] instances, which preserve the entry-definition order, just like PowerShell’s [ordered] @{ ... } hashtables[1]; in v7.2-, they were regular [System.Collections.Hashtable] instances.

    • Either way, however, in order to be JSON-compliant, the hashtables returned by ConvertFrom-Json are case-sensitive with respect to key lookups, unlike PowerShell’s regular hashtables (@{ ... }, [ordered] @{ ... }).

    • Choosing whether to use -AsHashTable or not:

      • While using hashtable object graphs is generally preferable (lighter-weight, easier to modify), there are situations where obtaining [pscustomobject] graphs is still a must, given that hashtables and objects aren’t fully interchangeable.

      • Conversely, if your JSON contains object with property names that are mere case variations of each other, -AsHashTable is a must, given that true property access in PowerShell is inherently case-insensitive; e.g.:

        # !! FAILS, because a [pscustomobject] instance cannot
# !! have property names that differ in case only.
'{ "foo": 1, "FOO": 2 }' | ConvertFrom-Json

# OK - the hashtable returned is case-sensitive.
'{ "foo": 1, "FOO": 2 }' | ConvertFrom-Json -AsHashTable

    [1] These literals become [System.Collections.Specialized.OrderedDictionary] instances, which, in fact, the OrderedHashtable implementation uses behind the scenes as well, albeot case-sensitively.

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