I have multiple models that need to have their history kept pretty much indefinitely or at least a very long time. The application I would keep track of daily attendance statistics for people in different organizations, and a couple of other similar associations. I've realized that I can't ever delete users due to the user not showing up in a query for attendance anytime before said user was deleted. The problem I'm having is finding a nice way of keep track of old associations as well as querying on those old associations.
If I have a connecting table between Users and Organizations, I could just add a new row with the new associations between a User and the Organization the user belongs to, and query on the old ones based on the date, but I really don't have any elegant way of doing this, everything just feels ugly. I was just wondering if anyone has dealt with anything like this before, and maybe had a solution they had already implemented. Thanks.
From a modeling point, the relationship sounds like the one between Employee and Employer, namely Employment. This would hold a reference to both Employee and Employer along with some notion of the TimePeriod (ie, startDate and end Date). If you wanted to query 'active' employees then they are all the ones with a startDate <= Now() && endDate >= Now(), 'terminated' employees have endDate < Now(), etc.
I can't tell in your case what the relationship is between Users and Organizations, and what makes the relationship start and end, but a concept similar to Employment, Membership, Enrollment or Contract is likely there. When you say daily attendance, is it not daily over a period of time? The time period is the basis for your queries.
Hope that helps,
Berryl
Create an is_deleted field so that you can still query those "deleted" users, but modify your code so that they will behave everywhere else as if they are deleted. Then you never need to actually delete the row and lose data.
There are a number of plugins that keep track of revisions to models, including their associations. Take a look at this search for revision-related plugins.
Related
I'm building a site that tracks donations and sales of items in a school auction.
Items can be sold individually or in lots, which are just groups of items bundled for sale as a single unit (like a gift certificate for a dinner Item bundled with a gift certificate for movie tickets Item).
Both of these things (Items and Lots) share fields like name, description, value. But Items have additional fields, like the donor, restrictions of use, type of item, etc.
I started by creating a table called Lot and an association table that lets Lots contain 1+ Items.
That works great for Lots. But that leaves me with a problem:
When Buyers win I need to record the win and the price. I'm doing that with a Win table that associates the Buyer with the Lot and the winning price.
But how do I deal with all the Items that aren't assigned to Lots? Should every item be in a Lot, just singly? That would make sense because it would work with the Win table scheme above, but I would need to automatically create a Lot for every Item that isn't already in another Lot. Which seems weird.
I'm sure this is a simple problem, but I can't figure it out!
Thanks!
Your approach of treating every item as a lot should be the winning one. It may sound weird, but it will make things way easier in the long run.
I have to deal on a daily base with a database where a similar problem was 'solved' the other way round, meaning keeping bundles of items and items apart and that proved to be a great pita (and for sure I'm not talking about a flat round bread here).
This database is both backbone for statistical evaluations and a bunch of (web) applications and on countless occasions I run into trouble when deciding which table to chose or how to level the differences between those two groups in querying and in coding.
So, even if your project will be rather small eventually, that is a good idea.
Yes, you need to provide a method to put every item in a lot, but this trouble is to be taken just once. On the other hand your queries wouldn't become significantly more complex because of that 'extra' table, so I'd definitely would chose this way.
It sounds like you have an Auction model that could have one or many Items. Then you could have two different types of Auctions, Auction::Single and Auction::Lot. Price would be a column on Auction. Auction has many Bids which is a join model between the Auction and the User (or Bidder). That join model would also store the bid price. When the Auction is over, you could create a separate Win record if you want, or just find the Winner through the highest Bid from Auction.
It would be helpful if you showed some code. But, what you want is a polymorphic association. So, something like:
class Item
has_one :win, as: :winnable
belongs_to :lot
end
class Lot
has_one :win, as: :winnable
has_many :items
end
class Win
belongs_to :buyer
belongs_to :winnable, polymorphic: true
end
This is probably quite simple but i'm having a little trouble getting this right.
I have a User model and Event model. Both have the usual created_at attribute. Users can have many events and an event belongs to a user.
What want to do is write something in active record to give me all users that have not created an event since a given date.
I have managed to do it with multiple loops but it's highly inefficient. Is it possible to do this efficiently with one statement or perhaps a named scope?
I have a named scope to count events by users:
scope :user_event_count,
select("users.id, count(events.id) AS events_count").
joins(:events).
group("users.id").
order("events_count DESC")
I'm wondering if similar is possible, but am having trouble working out how to find the last event a user submitted.
Can anyone point me in the right direction?
Here is a break up about how to achieve this.
Select all users for all events that were created since a given date
Select all users who are not in the above set
subquery = Event.select("user_id").where("created_at >= :start_date", {start_date: params[:start_date]}).to_sql;
User.where("id NOT IN (#{subquery})")
Hope this helps.
It sounds like what you want is the users for whom the maximum event creation date is prior to some time.
scope :user_event_count,
select("users.id, max(events.created_at) AS max_event_created_at").
joins(:events).
group("users.id").
having("max(events.created_at) < :start_date")
If you had a very large number of events it might be more efficient to structure it as a query where there exists an event prior to a particular time and there does not exist an event since that time.
This is what I want:
It is like an appointment system/personal schedule. For example, a doctor have 4 periods of working time(sessions) everyday, and in each session he will have some patient to meet(the number in the table field). So His schedule look like the picture above.
At first thought, it looks like: Every day has many sessions. And a session contains some other information like the number of patients, etc. (and do not need to set its specific time period. )
The problem is how to set this up? I just have no clue about what the model should like. How should Session relates to Time/Day? And it seems Day and Session are already created.
I feel this could just be done with Session model, the model could contain some time attribute to sort them like the mock-up above.
I have checked some calender gem/plugin( e.g fullcalender), but they does not seem to help this problem.
This could easily be done with a Sessions model with enough logic to enforce your rules. You will probably want to associate a Doctors model with a Patients model through Sessions, but I don't know enough about your needs to be sure.
You should review the Rails Guide on ActiveRecord Associations for details on how to create associations and for ideas that may help you. One of the examples (2.4 The has_many :through Association) involves doctors and patients and is similar to what you describe.
I am considering developing an application using Ruby on Rails that is a planner of sorts. I would like to give a user the ability to see a list of days, click a particular day, and then add things like: Meals, Expenses, Events, Todos, and Exercises. Really I am doing this for me and my growing family.
I am curious with how best to implement this. I can certainly see that Meals, Expenses, etc. need to belong_to :user but I am curious how to implement the belongs_to :day or something like that. Using the created_at or updated_at wouldn't necessarily allow me to provide views for future dates.
I can see how if I created a Days table and then added days through a time and date field that this would work but seems a little strange to ask people to create the actual days.
Or perhaps instead of that I could just create links to variables that search for #today, #tomorrow, but that would get messy.
I have browsed for gems/plugins but can't find one that works. Ideally a person would be able.
Anyone have any thoughts on how to implement something like this?
There are a number of existing Rails calendars, such as http://github.com/elevation/event_calendar or http://github.com/topfunky/calendar%5Fhelper.
However, to answer your specific question about dates: I don't think there's any need to have Day as a model; simply give each event a start date and time, and an end date and time. Remember that Ruby makes it easy to search based on ranges, so "give me all of the events next week" is a cinch if each event has dates and times associated with it.
I'll give it a shot...
Two tables; users and events. A user has many events and an event belongs to a user. Meal, Expenses, etc. are various types of Event. Within events, you can have fields for start and end time of the events. If needed (lets say an events last over multiple days), you could remove the day/time when events occurs into it's own table.
This way, when displaying the calendar for a user, you can find all the events for that date. If none are found, then display nothing.
What do you think?
I would add a model called "Events" and have a properties of the model to represent start date/time, end date/time. I do not think you need a Days model, you can generate your calendar view from the Date class built into ruby.
I have done same kind of project for the Event management in training institute. At there I used event_calender plug in with rails. (enter link description here)
In there we just need to create Event model only. Then we can easily work with that.
Does anyone know of any method in Rails by which an associated object may be frozen. The problem I am having is that I have an order model with many line items which in turn belong to a product or service. When the order is paid for, I need to freeze the details of the ordered items so that when the price is changed, the order's totals are preserved.
I worked on an online purchase system before. What you want to do is have an Order class and a LineItem class. LineItems store product details like price, quantity, and maybe some other information you need to keep for records. It's more complicated but it's the only way I know to lock in the details.
An Order is simply made up of LineItems and probably contains shipping and billing addresses. The total price of the Order can be calculated by adding up the LineItems.
Basically, you freeze the data before the person makes the purchase. When they are added to an order, the data is frozen because LineItems duplicate nessacary product information. This way when a product is removed from your system, you can still make sense of old orders.
You may want to look at a rails plugin call 'AASM' (formerly, acts as state machine) to handle the state of an order.
Edit: AASM can be found here http://github.com/rubyist/aasm/tree/master
A few options:
1) Add a version number to your model. At the day job we do course scheduling. A particular course might be updated occasionally but, for business rule reasons, its important to know what it looked like on the day you signed up. Add :version_number to model and find_latest_course(course_id), alter code as appropriate, stir a bit. In this case you don't "edit" models so much as you do a new save of the new, updated version. (Then, obviously, your LineItems carry a item_id and an item_version_number.)
This generic pattern can be extended to cover, shudder, audit trails.
2) Copy data into LineItem objects at LineItem creation time. Just because you can slap has_a on anything, doesn't mean you should. If a 'LineItem' is supposed to hold a constant record of one item which appeared on an invoice, then make the LineItem hold a constant record of one item which appeared on an invoice. You can then update InventoryItem#current_price at will without affecting your previously saved LineItems.
3) If you're lazy, just freeze the price on the order object. Not really much to recommend this but, hey, it works in a pinch. You're probably just delaying the day of reckoning though.
"I ordered from you 6 months ago and now am doing my taxes. Why won't your bookstore show me half of the books I ordered? What do you mean their IDs were purged when you stopped selling them?! I need to know which I can get deductions for!"
Shouldn't the prices already be frozen when the items are added to the order? Say I put a widget into my shopping basket thinking it costs $1 and by the time I'm at the register, it costs $5 because you changed the price.
Back to your problem: I don't think it's a language issue, but a functional one. Instead of associating the prices with items, you need to copy the prices. If every item in the order has it's own version of a price, future price changes won't effect it, you can add discounts, etc.
Actually, to be clean you need to add versioning to your prices. When an item's price changes, you don't overwrite the price, you add a newer version. The line items in your order will still be associated with the old price.