I'm trying to look up 1 instance of a model via a slug, which I can do via
#project = Project.where(:slug => params[:id]).first
But once I get the instance I want to find the next and previous instances of the model from a order of a column called publish which is a date.
how would I get the slug only of the previous and next instance of my arbitrary order by column?
::Edit::
Adding this to my modeled worked.
def previous(offset = 0)
self.class.select('slug').first(:conditions => ['published < ?', self.id], :limit => 1, :offset => offset, :order => "published DESC")
end
def next(offset = 0)
self.class.select('slug').first(:conditions => ['published > ?', self.id], :limit => 1, :offset => offset, :order => "published ASC")
end
I found this solution at Next, Previous Records Using Named Scope
Assuming your publish dates are unique something like this ought to work:
#project = Project.where(:slug => params[:id]).first
#prev_project = Project.where( "publish < ?", #project.publish ).
order( "publish DESC" ).
first
#next_project = Project.where( "publish > ?", #project.publish ).
order( "publish" ).
first
For #prev_project the where clause indicates all Projects before #project, the order lists them latest first (which puts the one right before #project at the top) and first limits the query to one result, i.e. the previous Project. The query for #next_project is the same but reversed. If publish isn't unique you'll have to sort on a second criterium as well.
However, you may want to consider not reinventing the wheel and using the very common gem acts_as_list, which would make this as simple as #project.higher_item and #project.lower_item.
Related
I have two models, post and comment. Posts has many comments and comments belongs to posts.
What I'm trying to do, is to have a list of posts that is ordered by creation date, unless it has comments. Then it needs to take the creation date of the latest comment.
Now I know that I can include associations like this:
Post.find(:all, :include => [:comments], :order => "comments.created_at DESC, posts.created_at DESC")
But this will order all posts with comments first and then the posts without comments. I don't want either ones ordered separately, but combined.
The solution also needs to be compatible with a paginate gem like will_paginate.
Edit
I have it now working with the following code:
posts_controller.rb
#posts = Post.order('updated_at DESC').page(params[:page]).per_page(10)
comments_controller.rb
#post = Post.find(params[:post_id])
#post.update_attributes!(:updated_at => Time.now)
I'd recommend:
Add a last_commented_at date field to your Post model. Whenever someone comments on the post update that field. It de-normalizes your db structure a bit, but your query will be faster and more strait-forward.
Postgres
Post.paginate(:include => [:comments],
:order => "COALESCE(comments.created_at, posts.created_at)",
:page => 1, :per_page => 10)
MySQL
Post.paginate(:include => [:comments],
:order => "IFNULL(comments.created_at, posts.created_at)",
:page => 1, :per_page => 10)
I'm trying to do something along the following lines:
if start_date?
query = where("datetime > :start_date", :start_date => start_date)
end
if end_date?
query = where("datetime <= :end_date", :end_date => end_date)
end
if client
query = where("client.name LIKE :client", :client => client)
end
if staff
query = where("staff.name LIKE :staff", :staff => staff)
end
paginate :per_page => 20, :page => page,
:conditions => query,
:order => 'datetime'
I can't find any examples though of how to build up a query and use it along with paginate plugin. Of course the query isn't correct yet as I've got to figure out how to do the joins so I can query against the other properties in other tables, but other than that, how do you build up queries to use in the conditions?
You want to put the .paginate call on the end of the chain of where calls, like this (all one line, split up for readability)
SomeClass.where("datetime > :start_date", :start_date=>start_date).
where("datetime < :end_date", :end_date=>end_date).
paginate(:per_page=>20,:page=>page)
If you want to conditionally add the conditions, you can do that too, like:
x = SomeClass
x = x.where("datetime > :start_date", :start_date=>start_date) if start_date
x = x.where("datetime < :end_date", :end_date=>end_date) if end_date
x.paginate(:per_page=>20,:page=>page)
You can try this if you installed kaminari gem :
ModelName.where( your_query ).page(params[:page]).per(50)
.where() returns ActiveRecord::Relation
.paginate()'s :conditions parameter has to be an array of conditions as if it was an argument of .where().
You should fix your code as next:
if start_date?
query = ["datetime > :start_date", :start_date => start_date]
end
etc.
ActiveRecord Relation doesn't have paginate method
Say I have simply ran rails g scaffold book name:string about:text On the 'show' view, how would I implement a button to go to the next item in the model.
I can't simply do #next = #book.id + 1 because if #book.id = 2 (for example) and I clicked destroy on the book with an id of 3. It would result in a broken page.
You can do:
#next = Book.first(:conditions => ['id > ?', #book.id], :order => 'id ASC')
Remember to check whever #next is not nil
To be even cooler, you can create a method in your model like so:
def next
Book.first(:conditions => ['id > ?', self.id], :order => 'id ASC')
end
then if you have #book you should be able to invoke it like
#book.next
haven't written anything in RoR recently but this looks reasonable to me;)
In my application, Annotations are considered "accepted" if either:
They have been explicitly marked "accepted" (i.e., their state == 'accepted')
They were last updated by a user who has the "editor" role
My question is how to find all accepted explanations with a single DB query. Basically I'm looking for the database-driven version of
Annotation.all.select do |a|
a.last_updated_by.roles.map(&:name).include?('editor') or a.state == 'accepted'
end
My first attempt was
Annotation.all(:joins => {:last_updated_by => :roles}, :conditions => ['roles.name = ? or annotations.state = ?', 'editor', 'accepted'])
But this returns a bunch of duplicate records (adding a .uniq makes it work though)
Changing :joins to :include works, but this makes the query way too slow
Are the results of your first attempt just wrong or do they only need an ".uniq"?
Have you tried
:include => {:last_updated_by => [:roles]}
instead of the join?
or making two queries
#ids = Editor.all(:conditions => ["role = 'editor'"], :select => ["id"]).map{|e|e.id}
Annotation.all(:conditions => ["last_updated_by in (?) or state = ?", #ids.join(","), "accepted"]
is that any faster?
I have a model for which I want to retrieve the next record(s) and previous record(s). I want to do this via a named_scope on the model, and also pass in as an argument the X number of next/previous records to return.
For example, let's say I have 5 records:
Record1
Record2
Record3
Record4
Record5
I want to be able to call Model.previous or Model.previous(1) to return Record2. Similarly, I want to be able to call Model.next or Model.next(1) to return Record4. As another example I want to be able to call Model.previous(2) to return Record3. I think you get the idea.
How can I accomplish this?
To implement something like 'Model.previous', the class itself would have to have a 'current' state. That would make sense if the 'current' record (perhaps in a publishing scheduling system?) was Record3 in your example, but your example doesn't suggest this.
If you want to take an instance of a model and get the next or previous record, the following is a simple example:
class Page < ActiveRecord::Base
def previous(offset = 0)
self.class.first(:conditions => ['id < ?', self.id], :limit => 1, :offset => offset, :order => "id DESC")
end
def next(offset = 0)
self.class.first(:conditions => ['id > ?', self.id], :limit => 1, :offset => offset, :order => "id ASC")
end
end
If so you could do something like:
#page = Page.find(4)
#page.previous
Also working would be:
#page.previous(1)
#page.next
#page.next(1)
Obviously, this assumes that the idea of 'next' and 'previous' is by the 'id' field, which probably wouldn't extend very well over the life of an application.
If you did want to use this on the class, you could perhaps extend this into a named scope that takes the 'current' record as an argument. Something like this:
named_scope :previous, lambda { |current, offset| { :conditions => ['id < ?', current], :limit => 1, :offset => offset, :order => "id DESC" }}
Which means you could call:
Page.previous(4,1)
Where '4' is the id of the record you want to start on, and 1 is the number you want to navigate back.
I added this feature into my gem by_star last month. It may have some other features you're interested in, so check it out.
It works by you having an existing record and then calling previous or next on that:
Page.find(:last).previous
I wrote a gem for doing this for arbitrary order conditions, order_query:
class Issue < ActiveRecord::Base
include OrderQuery
order_query :order_display, [
[:priority, %w(high medium low)],
[:valid_votes_count, :desc, sql: '(votes - suspicious_votes)'],
[:updated_at, :desc],
[:id, :desc]
]
def valid_votes_count
votes - suspicious_votes
end
end
Issue.order_display #=> ActiveRecord::Relation<...>
Issue.reverse_order_display #=> ActiveRecord::Relation<...>
# get the order object, scope default: Post.all
p = Issue.find(31).order_list(scope) #=> OrderQuery::RelativeOrder<...>
p.before #=> ActiveRecord::Relation<...>
p.previous #=> Issue<...>
p.position #=> 5
p.next #=> Issue<...>
p.after #=> ActiveRecord::Relation<...>