PowerShell – Create collections of custom objects

Background

Today a colleague asked my how he could store object collections in memory (a PowerShell variable) instead of writing and reading to/from CSV files. While searching for it he found tons of examples but most were written specifically for one target, he needed something more basic and flexible. He asked me if I already had a topic about it on my blog. Sadly I had to disappoint him, it wasn’t on my blog, yet. However I knew the answer and I will now also share this on my blog.

Creating the collection

Lets start of with creating an ArrayList in PowerShell:

Done. This is our generic collection, it can contain any PowerShell (.NET) object.

Before adding items to the collection be very aware that the fields of the first item added dictate which fields the collection will have.

For example take object $A and object $B.
Object $A has two string fields: “fieldA” and “fieldB”
Object $B also has two string fields: “fieldB” and “fieldC”
If object $A is added to our new empty collection, the collection would then have two fields: “fieldA” and “fieldB”.
If we would then add $B to the same collection the item in the collection would have an empty value in the field “fieldA” and no field “fieldC” (fieldB would be added normally to the list).
Keep this in mind when adding different types of objects to a collection.

Creating a custom object

Creating a custom object is easy:

This creates an empty System.Object object. This Object has no fields and only has four methods:
bool Equals(System.Object obj)
int GetHashCode()
type GetType()
string ToString()

This makes it an ideal object to start with as we can manually define every field.

So how do we add fields to our empty object?

Like this:

This example create a field named “Field1” with the value “value”, you can also pass a variable as value or even a field of a different object. For adding multiple field just repeat the line with different “Name” values.

This method can also be used to add fields to existing objects. For example you can read a csv file, add fields (for example a calculated field based on values of other fields) to the objects and then add all of those to a new (empty) collection which you can then write to a csv again or process further.

Adding the custom object to the ArrayList

We now have an ArrayList and need to put our custom object in it.

For people who are used to .NET and the way the lists work the method will be mostly unsurprising. There is only one thing to keep in mind, the Add method returns the index for the new item in the array. If you do not need this (and don’t want a series of indexes appearing on the console) you could output the result to null as in below example:

This will add the custom object to our ArrayList and will ignore the returned value.

Putting it all together

For this example I add ten objects to an ArrayList; the ten objects are the same but you can modify this to your own specific situation.

If I would then call $collectionWithItems it will return the collection. This is what the output is of $collectionWithItems when called after the for loop:

Update (2017-06-13): Quicker/dirtier way to create objects with certain fields

Another way (though less pretty) is to do a select statement on any object, this will create a PSCustomObject with only the selected properties. Instead of the above example where it took 4 lines to create an object with 3 properties, this object can be created with all three fields in 1 line. However adding the contents to the fields might still require some additional lines which makes it also end up with 4 lines to create and fill the object.

 

Collect site collection information from Office 365

Collecting users and groups from Office 365 is a relatively long running script (as mentioned in my previous post). Fortunately collection more general site collection information is easier. There is not very much data that can be collected, this is because a limitation in PowerShell’s access to SharePoint Online (before the upgrade to SharePoint 2013 this was not possible at all for SharePoint Online).

This script is a fairly short one but can be expanded in several ways (of which I will offer a few suggestions).

What it all comes down to can be summarized in this one-liner (don’t forget you will need to be connected to the Office 365 Service and the SharePoint Online service before running the scripts on this post):

In this case you may replace the variable $outputPath with the path where you want to have the results written to.

The following example is what I use at a client to monitor site collection storage quota’s (among with a few other things):

Now compared to the one-liner it may seem a bit overwhelming, but the output will be more relevant then before (where all values of all sites where returned).

For example if you pass the parameter -selectSites you will be able to select the sites from which you want to collect data (which I personally find the easiest way to choose which sites I want to receive details about), another option would be to replace the Out-GridView by a Where-Object and filter the results in that way.

In lines 25 through 28 I calculate the percentage of the assigned stored that is in use. If you are not interested in this number you can simply remove this from the script (in this casealso remove line 37 which will try to write the percentage), however I think that in most cases this is relevant and useful information. You could also add other calculations (for example a percentage of used Resources or the ammount of sub webs).

The part from line 30 through 38 does nothing more than adding only the data that is relevant for my report to the output. If you want to collect additional information (like Resource usage etc.) you can add this to the $temp object just like the other properties are added.