silverstripe-blog/docs/en/configuring-large-websites.md

Configuring Blog for large user bases

By default the blog module user and author selection form fields include all users in your website as candidates for writers, editors and contributors. Additionally, when adding a blog post, again all users are selectable. This can cause issue with websites that store a large number of users in the database.

In this case you may need to restrict the number of user accounts that are elegable to be selected. The module has some useful configuration options for this that can be added to your projects config.yml

Restricting blog managers to a permission setting

Default is to list all users and when one is selected, they are added to a blog-users group with CMS_ACCESS_CMSMain permissions. To only include those already having these permissions you can set in your config.yml:

Blog:
  grant_user_access: false

Note: depending on the incusion order of your config.yml you may need to clear the condifg setting before updating it. In this case use the folling in yout mysite/_config.php:

Config::inst()->remove('Blog', 'grant_user_access');

If you create your own permission and want to ensure the pool of possible selectable users includes those with this permission you can set the checked permission in config.yml with:

Blog:
  grant_user_permission: SOME_PERMISSION_here

Restricting blog post authors selection to a known group

In a blog post when selecting an author it will default to you (the logged in person creating the post), however you may be posting on behalf of another person. In this case the slection form field will offer all users as potential blog authors. Again for large websites with many thousands of users this can cause the site to be slow or non-responsive. We can turn on a filter so that authors need to be in a defined user group to be able to be selected as an author.

Enable this in your config.yml by adding a group code:

BlogPost:
  restrict_authors_to_group: 'group_code'

Extension points in Blog and BlogPost users and how to use

Both Blog and BlogPost have methods which return the list of candidate users or authors. If the previously mentioned mothods of reducing this list are not suitable or you wish to roll your own, you can utilise a DataExtension to get the controll you require.

For example in BlogPost:

protected function getCandidateAuthors() {
		if($this->config()->get('restrict_authors_to_group')) {
			return Group::get()->filter('Code', $this->config()->get('restrict_authors_to_group'))->first()->Members();
		} else {
			$list = Member::get();
			$this->extend('updateCandidateAuthors', $list);
			return $list;
		}
	}

Note the line $this->extend('updateCandidateAuthors', $list); which allows you to call a updateCandidateAuthors method in a DataExtension to the Blog Post class if you have not set a restrict_authors_to_group config, further filter the passed in Member list before it gets sent back to the form field.

See the documentation on DataExtension for further implementation notes.