Q:

Get blog post custom field in template head - Sitefinity

I need to set several meta tag values in my page head to values set in blog post custom fields.  
How do I access the blog item viewmodel from the head?  
I've created a separate MVC view snippet for my custom head and referenced it in my template's layout, that much works.  
Tried
I grab some of the same custom field values inside my blog template via references like Model. Item. Fields. MyFieldName. Fields. Title.  
Adding this same line to the head template throws a 
System. Web. HttpCompileException with little useful information attached.  I somewhat expected this, as I suspect that viewmodel for the blog post only exists in the context of the blog widget.  
Ends up that I need to rebuild after every change to the head cshtml file or I get this error.  Seeing as this is about a four-minute process with Sitefinity (15 seconds to build, 3:45 to do whatever Sitefinity does for about four minutes), this is a gruelingly horrid thing to have to do. 
However the Model is null at this level.  
Also tried 
Per the ever-helpful and highly knowledgeable @Veselin Vasilev, I looked into passing the data up via MetaDataFields.  I didn't see these options in my admin section for the widget.  To clarify, I'm using the built-in "Blog posts" widget with a customized view file.  

But if it's possible to do this, it gives me hope that there's a way to pass more data up, even if it's going to take some work. 

A:

EDIT: Sitefinity v.10.2 and above:
There is an easier way to achieve what you are trying - in Page edit mode, in the Blog Posts widget click Edit and then Advanced.  Then you should see a MetaDataFields button.  Click it and you should see several meta data related fields.  
In the MetaTitle field put the name of your custom field and save.  
Also, from the docs:

If you leave MetaTitle field empty, Sitefinity CMS adds takes its value from the Title field of the static content item or from the identifier field of a dynamic content item.  Otherwise, the  tag is populated with the contents of the field that you have entered in MetaTitle field. 

More details here:
https://docs.sitefinity.com/configure-meta-title-and-meta-description-on-widget-level
Sitefinity 10.1 and below:
Check this article 
Basically, in your view you get a reference to the Page object and then update its Header with the meta data you need.