HABTM relation find all records, excluding some based on association

Question

I\'ve looked at some of the similar SO posts relating to this but I\'m struggling to get my head around it.

I have a habtm relation between Projects and Users. I\'m tryi

Answer 1

You can place a scope in your Project model like so:

scope :not_belonging_to, lambda {|user| joins(:projects_users).where('projects_users.user_id <> ?', user.id) }}

This assumes your join table name matches rails convention for HABTM associations

To then get projects that a user doesn't belong to, first find your user, then pass them to the scope like so:

@user = User.find(params[:id]) # example
@unowned_projects = Project.not_belonging_to(@user)

On reflection, that scope won't work as it will find projects that have more than one developer, if one of those is your guy.

Instead, use the following:

scope :not_belonging_to, lambda {|user| where('id NOT IN (?)', user.projects.empty? ? '' : user.projects) }

Answer 2

From Matt's reply above, which was extremely helpful.

I had trouble with this for a while. I attempted to use the following:

scope :not_belonging_to, lambda {|developer| where('id NOT IN (?)', developer.projects.empty? ? '' : developer.projects) }

But I received the following error:

SQLite3::SQLException: only a single result allowed for a SELECT that is part of an expression:

I found I needed to update the scope, adding .ids on the end. See below:

scope :not_belonging_to, lambda {|developer| where('id NOT IN (?)', developer.projects.empty? ? '' : developer.projects.ids) }