Do-untill loop getting error (powershell) - json

Question

Try to convert a web request from JSON but always get the below error:
Method invocation failed because [Microsoft.PowerShell.Commands.BasicHtmlWebResponseObject] does not contain a method named 'op_Addition'.
At C:\Users\gmicskei\Desktop\lastlogin_users_azureAD.ps1:39 char:17
+ $QueryResults += $Results
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (op_Addition:String) [], RuntimeException
+ FullyQualifiedErrorId : MethodNotFound
Here is my code:
do {
$Results = Invoke-WebRequest -Headers $authHeader1 -Uri $Uri -UseBasicParsing -Method "get" -ContentType "application/json"
if ($Results.value) {
$QueryResults += $Results.value
} else {
$QueryResults += $Results
}
$uri = $Results.'#odata.nextlink'
} until (!($uri))
$QueryResultsjson = $QueryResults | ConvertFrom-Json
Can you please advise?
Thanks,
Gabor

Answer 1

The objects returned by Invoke-WebRequest -UseBasicParsing are of type Microsoft.PowerShell.Commands.BasicHtmlWebResponseObject:
This type has no .Value property.
Using it as-is, which your code therefore does, is the source of the problem:
In the first loop iteration, $QueryResults += $Results stores the $Results variable as-is.
In subsequent loop iterations, += tries to "add" to an instance, but no such operation is defined for this type.
As an aside: In order to collect the $Results values in an array, $QueryResults would have to be initialized as an array before entering the loop, but note that building an array iteratively with += should be avoided, due to its inefficency - see this answer.
You can solve all problems by using Invoke-RestMethod instead, which automatically parses JSON responses into objects ([pscustomobject] instances):
$results = do {
# Calls the web service and automatically parse its JSON output
# into an object ([pscustomobject] instance).
$result = Invoke-RestMethod -Headers $authHeader1 -Uri $Uri -Method "get" -ContentType "application/json"
# Output the result at hand, to be collected across all
# iterations in the $results variable being assigned to.
# (.value is assumed to be a top-level property in the JSON data received).
$result.value
# Determine the next URI, if any.
# Since $result is now an *object*, property access should work.
$uri = $result.'#odata.nextlink'
} while ($uri)