Getting the PbiServiceModelId so we can change the dataset against a report (pbix file).

Currently there is no straight forward approach to retrieve PbiServiceModelId(numeric digit) using API. 

There are multiple workarounds you could try to do the automation. I have followed below mentioned approach. 

1. Deploy Model.pbix to pbi service. 

2. Login to powerbi.com to grab the PbiServiceModelId.  After logging in navigate to any workspaces, it makes a call to SharedDatasets to fetch all datasets.  You could grab the right one. 

3. You can use below ZipUnZip function to update the connection.

function Set-DatasetId([string] $directoryPath, [string] $reportName)
{

$zipFileName = "$($directoryPath)\$($reportName).zip"
$pbiFileName = "$($directoryPath)\$($reportName).pbix"
Copy-Item $pbiFileName $zipFileName -Force

$unZippedirname = "$($directoryPath)\$($reportName)"
Expand-Archive -Path $zipFileName -DestinationPath $unZippedirname -Force -Verbose
Write-Host "$($directoryPath)\$($reportName)"
$securityBindingsFileName = "$($unZippedirname)\SecurityBindings"
Remove-Item -Path $securityBindingsFileName -Force -ErrorAction SilentlyContinue

$connectionFileName = "$($unZippedirname)\Connections"
$fileContent = (Get-Content -Raw $connectionFileName) -replace $global:orgdatasetId, $global:PPACModelDatasetId
$fileContent = $fileContent -replace $global:orgModelId , $PpacModelId
$Utf8NoBomEncoding = New-Object System.Text.UTF8Encoding $False
[System.IO.File]::WriteAllLines($connectionFileName, $fileContent, $Utf8NoBomEncoding)

$contentTypesFileName = "$($unZippedirname)"
Get-ChildItem "$contentTypesFileName" -Filter *.xml | Sort-Object -desc |
Foreach-Object {
$contentTypeorg= $_.Name
$filenameExracted= $_.Name.Replace("[","``[").Replace("]","``]")

if ($filenameExracted -eq "``[Content_Types``].xml")
{
$filenameExracted= $contentTypesFileName+'\'+ $filenameExracted
$fileContent = (Get-Content -Raw $filenameExracted) -replace '<Override PartName="/SecurityBindings" ContentType="" />', ''
$Utf8NoBomEncoding = New-Object System.Text.UTF8Encoding $False
#[System.IO.File]::WriteAllLines($_.FullName, $fileContent, $Utf8NoBomEncoding)
}
}

$ZipDirName = "$($unZippedirname)\*"
Compress-Archive -Path $ZipDirName -DestinationPath $zipFileName -Update -Verbose
Remove-Item -Path $pbiFileName -Force -ErrorAction SilentlyContinue -Verbose
Copy-Item $zipFileName $pbiFileName -Force -Verbose
Write-Host "PowerBI file $($reportName) are updated with dataset"
}