Converting a Datarow to a JSON object with PowerShell

This is just a quick post. As is frequent with these they are as much for me to refer to in the future and also because the very act of writing it down will aid me in remembering. I encourage you to do the same. Share what you learn because it will help you as well as helping others.

Anyway, I was writing some Pester tests for a module that I was writing when I needed some sample data. I have written before about using Json for this purpose This function required some data from a database so I wrote the query to get the data and used dbatools to run the query against the database using Get-DbaDatabase

Simple enough. I wanted to be able to Mock $variable. I wrapped the code above in a function, let’s call it Run-Query

Which meant that I could easily separate it for mocking in my test. I ran the code and investigated the $variable variable to ensure it had what I wanted for my test and then decided to convert it into JSON using ConvertTo-Json

Lets show what happens with an example using WideWorldImporters and a query I found on Kendra Littles blogpost about deadlocks

If I investigate the $variable variable I get

data results

The results were just what I wanted so I thought I will just convert them to JSON and save them in a file and bingo I have some test data in a mock to ensure my code is doing what I expect. However, when I run

I get

json error.png

and thats just for one row!

The way to resolve this is to only select the data that we need. The easiest way to do this is to exclude the properties that we don’t need

which gave me what I needed and a good use case for -ExcludeProperty

json fixed.png

Max Length of a column in a DataTable in PowerShell

Whilst I was writing my Test-DbaLastBackup Posts I ran into a common error I get when importing datatables into a database

I was using this table

01 - table

and when I tried to add the results of the Test-DbaLastBackup I got this

02 -error.PNG

Exception calling “WriteToServer” with “1” argument(s): “The given value of type String from the data source cannot be converted to type nvarchar of the
specified target column.”
At line:356 char:4
+             $bulkCopy.WriteToServer($InputObject)
+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : InvalidOperationException

Hmm, it says that it can’t convert a string to a nvarchar, that doesn’t sound right.To find out what was happening I used a little bit of code that I use every single day

All errors from your current session are stored in the $error array so [0] accesses the most recent one and fl is an alias for Format-List and the force switch expands the object. This is what I saw

03 expanded error.PNG

System.Management.Automation.MethodInvocationException: Exception calling “WriteToServer” with “1” argument(s): “The given value of
type String from the data source cannot be converted to type nvarchar of the specified target column.” —>
System.InvalidOperationException: The given value of type String from the data source cannot be converted to type nvarchar of the
specified target column. —> System.InvalidOperationException: String or binary data would be truncated.

String or binary data would be truncated. OK that makes sense, one of my columns has larger data than the destination column but which one? Lets take a look at some of the data

SourceServer  : SQL2016N3
TestServer    : SQL2016N1
Database      : RidetheLightning
FileExists    : Skipped
RestoreResult : Restore not located on shared location
DbccResult    : Skipped
SizeMB        : 4.08
BackupTaken   : 3/19/2017 12:00:03 AM
BackupFiles   : C:\MSSQL\Backup\SQL2016N3\RidetheLightning\FULL\SQL2016N3_RidetheLightning_FULL_20170319_000003.bak

SourceServer  : SQL2016N3
TestServer    : SQL2016N1
Database      : TheCallofKtulu
FileExists    : Skipped
RestoreResult : Restore not located on shared location
DbccResult    : Skipped
SizeMB        : 4.08
BackupTaken   : 3/19/2017 12:00:04 AM
BackupFiles   : C:\MSSQL\Backup\SQL2016N3\TheCallofKtulu\FULL\SQL2016N3_TheCallofKtulu_FULL_20170319_000004.bak

SourceServer  : SQL2016N3
TestServer    : SQL2016N1
Database      : TrappedUnderIce
FileExists    : Skipped
RestoreResult : Restore not located on shared location
DbccResult    : Skipped
SizeMB        : 4.08
BackupTaken   : 3/19/2017 12:00:04 AM
BackupFiles   : C:\MSSQL\Backup\SQL2016N3\TrappedUnderIce\FULL\SQL2016N3_TrappedUnderIce_FULL_20170319_000004.bak

Hmm, its not going to be easy to work out which bit of data is too big here.

All I need to know is the maximum length of the columns in the datatable though so I have a little snippet that will do that for me

and the output looks like this

04 - max length.PNG

So we can quickly see that the backupfiles property is too big and change the table accordingly and no more error.

Its pretty quick too, scanning 105 rows in 56 milliseconds in this example
05 - how long.PNG

I keep this little snippet in my snippets list for PowerShell ISE which you can find here

Here is the code to add this as a snippet to ISE
and if you want to add it to your VSCode snippets then you need to edit the PowerShell.json file which is located in your user home AppData folder ‘C:\Users\User\AppData\Roaming\Code\User\snippets\powershell.json’ or by clicking File –> Preferences –> User Snippets and typing PowerShell
04 user snippets.gif

Then you can add this bit of json inside the curly braces


 

and you have your snippet ready for use

07 - snippet in vscode.gif

Happy Automating