descendent model belongs to parents models in TREE structure RAILS 4 - ruby-on-rails

I want to setup a work order system in a tree structure like so
so the workorder belongs to a tenant, but also belongs to the property he/she lives in, and belongs to the landlord.
I know I can't have belongs_to :through. I want to be able to see all of the work order submitted by each tenant, and see all work order per property, and per landlord.
so if a landlord click on an work order, it will say which house it is for, and which tenant submitted this order.
So what is the best way to model this? polymorphic? or just straight up, belongs to?

Work orders belong to tenants, properties, and landlords. A work order must have all of those set when it is created. Landlords have many properties. Properties have many tenants, tenants have many work orders.
To see all work orders submitted by a tenant just do tenant.workorders. To see all he work orders per property per landlord you need to get all of the landlord's properties and then get all of the work orders for each of those properties.

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associations in ruby on rails - user creates courses

I am currently trying to create a system which allows for specific users to create a Course record which can be enrolled in by many other users. I've tried a few association techniques such as has_and_belong_to_many, has_many :through and number of other setups but have been unable to get it right.
Basically all that I need is the following:
Course belongs to (is created by) a single User (foreign_id => admin_id).
Course has many enrolled Users (Join Table?).
User has many created Courses.
User can belong to many Courses.
If you have any idea how this would be accomplished I would greatly appreciate your input.
A pretty good design is Canvas LMS.
In short:
A User is just a user.
A Course is just a course.
An Enrollment is an association between a user and a course. An enrollment has a type, which is either a student, a teacher, a TA or an observer. Each type has its own set of permissions.
So, if a user is not in any course, he/she is nothing but a user. A user can at the same time be a teacher in course A and a student in course B. Also, he/she can be both a student and a TA in the same course.
You can add your own enrollment types in your application, such as creator.

Single model reading and writing to several tables in Rails

When registering to my website, users have to specify which company or group they are working for and then all the users are placed in one db table called users. I was wondering if it's possible to create a new table for every single company that registers and then put all users from that company to that one specific table while still having a single user model and a single controller.
I think you need multi-tenant application.
Here Each company/group can act as a tenant - all users are members of the tenant.
A simple library for this purpose is Milia
Please check the documentation and use accordingly.
It will save all companies users to the same table - But while retrieving apply the scope to find users of a particular tenant.
You don't need to create a table for each company. You need to create tables called Companies and Users that are in relation with each other. So User belongs_to company. Then when you are creating a user you pass company_id to that user. You can read more about it here: http://guides.rubyonrails.org/association_basics.html

How can I model the association in the following situation.?

I have the following association between entities in the system:
Store
Vendor
and User
store can have many vendors,
vendor can belong to multiple stores.
A user can have multiple stores, but if its a user who is related to vendor, say a person who works for that vendor, then the behavior of that user changes.
Also, for a store there can be multiple roles.
I tried polymorphic association, but since the behavior of the user changes depending on roles and whether he is a store user or a vendor user, I cannot use that.
STI can also not be used since a vast amount of columns will differ. Any ideas will be helpful.
If I'm understanding your requirements accurately you want to model:
A vendor can have many stores
A store can have many vendors
A vendor can have many users
A store can have many users
That would require a has_and_belongs_to_many relationship between vendor and store. It would also require a polymorphic association between user and vendor/store. You should be able to use a polymorphic association. That way you could manage system behaviour for each user by checking their roles and associations. If you created a polymorphic association named userable for example, you could user user.userable to get either the vendor or the store and vendor.users or store.users to access users for those instances.
For your user model, regarding this line in your question:
"but if its a user who is related to vendor, say a person who works for that vendor, then the behavior of that user changes"
I would add a column to my user table called user_type and create some user types that you can use to filter out and assign privileges to. The user_type column could be a string field and explicitly named something like related and not_related, simply an integer 1 or 2, or more, or even a boolean field if there aren't going to be too many user_types.

Rails Devise users with multiple types - perhaps STI?

I have an application where there are users, which are managed by Devise. The application's actual users will add people as "friends" and one other type, lets call them "workers". The "friends" and "workers" are, or I would like them to be, all of type User, at the end of the day.
The catch is that there is a need for a User to be able to have a single person (User) in the system that is both a "friend" and a "worker" for them. There is also a need for non-duplication of Users by their unique id's, which in this case would be mobile phone number. If a given user adds another user as a "friend", and then subsequently adds them as a "worker", for example, it should simply be an association of some sort, and not a new User in the system.
I know how I would handle this in a traditional sense, but I'm sure there is some clever way with either STI or polymorphic associations to handle this in rails.
Any thoughts? It's worth noting that the various user types all have virtually identical fields (or will) associated with them - pretty straightforward id, name, mobile, etc.
I guess the trick is that any of the Users need to be able to have either or both of the "friend" or "worker" types associated to them, and each of those types should be able to have combinations of the other two associated with them.
It sounds to me like the whether someone is a friend or a worker should be an attribute of the join model between the two people rather than an attribute of either person.
That way a person can be a friend of one person and another person's worker.

Is this the right way to associate models in a domain with multiple users per account?

Using Rails and am new to it (and RDBMs). Have read lots of posts and articles on modeling and associations, but could really use a reality check on what I'm thinking for my particular case.
I have 3 main models: users, accounts, plans. The accounts are multi-user, with plans worked on by all users attached to the account (with varying privileges). If the account is destroyed I’ll also take down its users and plans.
Looks like the basic associations would be as follows. Is this correct?
users
belongs to - >
< - has many
accounts
has many ->
<- belongs to
plans
Is there any value in associating users with plans with “has many through”? I see that it would allow access like #user.plans and #plan.user[1], but can’t I access each via accounts, as in #user.account.plan?
Is it the case that with “has many through” the middle model simply belongs to the other two? All the examples I’ve seen show that. In my case, that would be inappropriate, since account actually owns the other two.
Is there a better way to model this (multiple users of an organization working on a set of one or more plans)?
Input is very much appreciated.
Your design is correct. The belongs_to terminology can indeed be a bit strange, but is proper. Use "has many through" if it makes your code more readable and obvious. (In other words, if the notion of a user having a plan makes sense, and is needed, go ahead and create the relationship. If it is more clear to conceive of the plan belonging to an account, then stick with user.account.plans.)
Your design should be sufficient so long as you don't need to restrict a user to a subsets of the plans belonging to an account, and so long as a user only belongs to a single account.

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