Simulate an inner join between two JSON responses of an API call

I have Googled and seen this: In PowerShell, what's the best way to join two tables into one?

However, how can I do the JOIN without having that? Because our PS does not come with it and I don’t think we have permission to install new commands and we are on 5.1 too. So it has to be something built-in.

Now the question:
I have two APIs that I call with Invoke-RestMethod and they send me a array of JSON response like so:

[
{ "FirstName" : "Hi",
"Code" : 123
},
{ "FirstName" : "Bye",
"Code" : 456
}
]

so let’s say we have $res1 and $res2 with some response like above in them and I want to do the JOIN on Code field.
How can I do this without using the Join-Object?

>Solution :

You can put your own simple Merge-Object command together like so:

function Merge-Object {
  param(
    [Parameter(Mandatory)]
    [array]$Left, 
    
    [Parameter(Mandatory)]
    [array]$Right, 
    
    [Parameter(Mandatory)]
    [string]$On)

  # create an index/correlation table from the right-hand collection
  # we'll use this to look up values based on the left-hand items' key property later
  $correlationTable = @{}
  $Right |ForEach-Object { 
    $key = $_.$On
    if ($null -ne $key) {
      $correlationTable[$key] = $_ 
    }
  }

  # iterate over the left-hand collection, try to correlate with right
  $Left |Where-Object {$null -ne ($key = $_.$On) -and $correlationTable.ContainsKey($key)} |ForEach-Object {
    # look up corresponding row in right-hand collection
    $correlated = $correlationTable[$_.$On]

    # extract property names from current object
    $existingNames = @($_.psobject.Properties.Name)

    # generate property selectors for non-overlapping property names on the right
    $selectors = $correlated.psobject.Properties.Name |Where-Object {$_ -notin $existingNames} |ForEach-Object {
      @{Name="$_"; Expression=[scriptblock]::Create("`$correlated.'$_'")}
    }

    # create new joined object
    $_ |Select-Object -Property @($existingNames;$selectors)
  }
}

Then use it like:

$res1 = @'
[
  {
    "FirstName": "Jane",
    "Code": 123
  },
  {
    "FirstName": "Robert",
    "Code": 456
  }
]
'@ |ConvertFrom-Json

$res2 = @'
[
  {
    "LastName": "Doe",
    "Code": 123
  },
  {
    "LastName": "Paulson",
    "Code": 456
  }
]
'@ |ConvertFrom-Json

Merge-Object -Left $res1 -Right $res2 -On Code |ConvertTo-Json

Which should give you:

[
  {
    "FirstName": "Jane",
    "Code": 123,
    "LastName": "Doe"
  },
  {
    "FirstName": "Robert",
    "Code": 456,
    "LastName": "Paulson"
  }
]