How to make an array available to all views

Hi,

I have an application layout that is used to create the general layout
for all pages.
However, I seem to struggle to find out how to declare variables like
arrays so that they are available everytime that layout or its related
partials are used.

Putting @myarray = MyArray.all into every action in every controller
doesn’t seem very dry, so I guess I’m just looking for a very simple
straighforward convention, but can’t seem to find it documented
anywhere or figure it out.

_caps

On Wed, Mar 10, 2010 at 9:54 AM, capsized [email protected]
wrote:

I have an application layout that is used to create the general layout
for all pages.
However, I seem to struggle to find out how to declare variables like
arrays so that they are available everytime that layout or its related
partials are used.

Putting @myarray = MyArray.all into every action in every controller
doesn’t seem very dry, so I guess I’m just looking for a very simple
straighforward convention, but can’t seem to find it documented
anywhere or figure it out.

Normally something like that goes into a high-level filter, like one
in ApplicationController.

Put a before_filter in your ApplicationController.

class ApplicationController
before_filter :set_my_array

private

def set_my_array
@myarray = MyArray.all
end
end

Cheers,

Andy


Andy J.
http://andyjeffries.co.uk/ #rubyonrails #mysql #jquery
Registered address: 64 Sish Lane, Stevenage, Herts, SG1 3LS
Company number: 5452840

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

It’s dirty, horrible, bad form, breaks the separation of layers…

Don’t call the model from the view!

Andy

On 10 March 2010 08:54, capsized [email protected] wrote:

straighforward convention, but can’t seem to find it documented
anywhere or figure it out.

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

Colin

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

It’s dirty, horrible, bad form, breaks the separation of layers…
Beware of the MVC police Colin, this suggestion will certanly not get
good housekeeping seal of approval :smiley:

I agree through. I’m not gonna add a before filter just to set
MyArray.all into a class variable. I’d rather call it directly and claim
to be pragmatic.

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

It’s dirty, horrible, bad form, breaks the separation of layers…
Beware of the MVC police Colin, this suggestion will certanly not get
good housekeeping seal of approval :smiley:

It’s not about MVC policing, I couldn’t give a monkey’s what you do in
your
app, but given that there is an easy way of handling it shouldn’t you
describe the correct method to any new developers.

I agree through. I’m not gonna add a before filter just to set
MyArray.all into a class variable. I’d rather call it directly and claim
to be pragmatic.

How do you work out duplicating a line of code in every action is being
“pragmatic”?

DRY mean anything to ya?

Cheers,

Andy

Sharagoz – wrote:

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

But you are wrong. The view should never, ever, ever touch the
database.

It’s dirty, horrible, bad form, breaks the separation of layers…
Beware of the MVC police Colin, this suggestion will certanly not get
good housekeeping seal of approval :smiley:

I agree through. I’m not gonna add a before filter just to set
MyArray.all into a class variable. I’d rather call it directly and claim
to be pragmatic.

Claim all you like. The fact is that in MVC architecture, database
queries don’t belong in the view. A before_filter is the proper place
for this.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

On 10 March 2010 15:15, Marnen Laibow-Koser [email protected]
wrote:

Sharagoz – wrote:

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

But you are wrong. The view should never, ever, ever touch the
database.

Is it considered ok to call model methods if they do not touch the db,
or are model methods forbidden also?

Colin

But you are wrong. The view should never, ever, ever touch the
database.

Is it considered ok to call model methods if they do not touch the db,
or are model methods forbidden also?

I would say the view can call instance methods of the model (attributes

real and virtual) but no class methods.

So:

<%= @user.name %>

is OK, but:

<% User.first.name %>

is not. It’s a bit of a contrived example, but there you go. Accessing
the
model through instance variables you’ve created is OK, going directly to
the
model bypassing the controller is not.

Cheers,

Andy

On 10 March 2010 17:19, Marnen Laibow-Koser [email protected]
wrote:

Is it considered ok to call model methods if they do not touch the db,
end

#my_action.html.erb
Good: <%= @person.name >

What about <%= @person.group_name %>
where Person belongs to Group and group_name is an instance method of
Person
def group_name
group.name if group
end

Bad: <% @person.save! =>

I would class the above as the unspeakable one actually.

Unspeakable: <% @people = Person.all %>

Colin

Colin L. wrote:

On 10 March 2010 15:15, Marnen Laibow-Koser [email protected]
wrote:

Sharagoz – wrote:

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

But you are wrong. �The view should never, ever, ever touch the
database.

Is it considered ok to call model methods if they do not touch the db,
or are model methods forbidden also?

I think it is appropriate for the view to call methods on the objects
passed in by the controller, provided that these methods do not change
the model or touch the database.

Example:

controller

def my_action
@person = Person.find(params[:id])
end

#my_action.html.erb
Good: <%= @person.name >
Bad: <% @person.save! =>
Unspeakable: <% @people = Person.all %>

Colin

Best,

Marnen Laibow-Koser
http://www.marnen.org
r[email protected]

Marnen Laibow-Koser wrote:

Example:

controller

def my_action
@person = Person.find(params[:id])
end

#my_action.html.erb
Good: <%= @person.name >
Bad: <% @person.save! =>
Unspeakable: <% @people = Person.all %>

Good example. I just want to throw in a couple more twists and see what
you think.

  1. What about methods on models that change themselves in some way?

<%= @post.last_viewed_at %>

Suppose the last_viewed_at method returned a previously stored time,
then updated the model to store a new current time. Maybe a bad example,
but I hope you get my meaning.

  1. What about aggregating class methods like count, sum or avg?

<%= Person.count %>

Obviously a class methods and does touch the database. I assume it would
be better to let the controller deal with stuff like this.

Controller
@person_count = Person.count

View
<%= @person_count %>

Thoughts anyone?

It’s dirty, horrible, bad form, breaks the separation of layers…

I don’t know what you mean by dirty, it saves several lines of code
and when looking at the view code it is easier to see what is
happening than to see a variable that has to be hunted for in a filter
somewhere to find out what it is.

It saves 4 lines of code, but breaks one of the principles of MVC
layered
separation. I’d say the 4 lines is worth it for keeping the application
clean.

Don’t call the model from the view!

@person.name is a model call from the view

I clarified my thoughts on this in a later post (10 March 2010 15:28),
might
I recommend reading that.

Cheers,

Andy

On 10 March 2010 12:10, Andy J. [email protected] wrote:

If it is literally something as simple as MyArray.all I believe there
is nothing wrong with calling the model direct from the view.

It’s dirty, horrible, bad form, breaks the separation of layers…

I don’t know what you mean by dirty, it saves several lines of code
and when looking at the view code it is easier to see what is
happening than to see a variable that has to be hunted for in a filter
somewhere to find out what it is.

It does not break the separation of layers any more than calling an
instance method of a model does when using something like
<%= @person.name %>

Don’t call the model from the view!

@person.name is a model call from the view

Colin

On Wed, Mar 10, 2010 at 11:48 AM, Robert W.
[email protected]wrote:

  1. What about methods on models that change themselves in some way?

<%= @post.last_viewed_at %>

Suppose the last_viewed_at method returned a previously stored time,
then updated the model to store a new current time. Maybe a bad example,
but I hope you get my meaning.

Don’t worry about it. What the method does itself shouldn’t be your
concern,
in the view. You want your code to be orthogonal, it shouldn’t matter
how
the variable returns returns the date, or what it does when you request
it,
that is the model’s prerogative. Trying to keep track all over your
application of what your model methods are doing requires you to know
and
consider their internal plumbing, this couples your code that you write
to
the model’s implementation. Something that won’t bite you on a small
app,
but will likely turn into a nightmare on a large app.

If your view has some object that the controller gave you, just consider
it
as an object you can access in whatever way that is necessary to perform
the
responsibilities of the view. Saving data is not a responsibility of the
view, so that should not happen there. Displaying the date it was
modified
may possibly be a responsibility of the view, so you can display that.
If
the model decides that it needs to do something every time someone asks
when
it was saved, your view shouldn’t know or care or change it’s behaviour
accordingly.

Really, your view shouldn’t even know it is an ActiveRecord object, it
should just be some object that has the information necessary to get
things
done. Then you can swap it out with other variables later, maybe a
struct or
an object pulled from a yaml file, or whatever.

  1. What about aggregating class methods like count, sum or avg?

<%= @person_count %>

Thoughts anyone?

A variable is better here, because your view shouldn’t know how to
tabulate
the size, that is business logic. What happens if you later add another
another type of user, and it should treat them as the same? What happens
if
different controllers want to render that same view to show their data?
Your
view knows too much about the data it is serving, it works for
Person.all,
but what if you add another type of person with different attributes,
stored
in the model OtherPerson ? Then you cant use that view (or you will have
to
change it, and change the controller for it).

To keep your code robust, keep your views stupid. To keep them stupid,
make
sure they are agnostic towards the implementation of displaying the
data.
Let the controller worry about that, that is why the controller exists.

http://www.youtube.com/watch?v=ku3QkWcPSEw

On Wed, Mar 10, 2010 at 4:36 PM, Andy J.
[email protected]wrote:

clean.

But think how many lines of code you are going to have to go edit when
you
realize that you need to change it.

Also, I wouldn’t consider Person.all to be more clean than @people. What
if
you need to exclude some? Person.all :conditions => {whatever}, if you
are
just using a before filter, it is easy to override, you can override it
for
any given controller, and for any given controller method. If it’s hard
coded into the view, then that view has to serve everybody’s wishes, it
ends
up having to know how it is to be used, and having lots of brittle
conditional code for each of these situations.

This is why the controller must be responsible for supplying the
appropriate
data to the view, not the view being responsible for creating it’s own
data.

It might start as innocently as Person.all, it can easily turn into
if this
Person.all
elsif that
OtherPerson.all
else
Person.all + OtherPerson.all
end

separation. I’d say the 4 lines is worth it for keeping the application
clean.

But think how many lines of code you are going to have to go edit when you
realize that you need to change it.

Did you misunderstand my post? I was arguing for putting it in a filter
rather than in the view (hence saying the 4 lines of before_filter,
private,
def and end was worth it).

It sounds like - when you start with “But” - that you disagree, but the
rest
of your post seems to be arguing from the same side as my posts.

Cheers,

Andy

On 10 March 2010 23:33, Josh C. [email protected] wrote:

If your view has some object that the controller gave you, just consider it
done. Then you can swap it out with other variables later, maybe a struct or

@person_count = Person.count
view knows too much about the data it is serving, it works for Person.all,
On Wed, Mar 10, 2010 at 4:36 PM, Andy J. [email protected]
separation. I’d say the 4 lines is worth it for keeping the application
up having to know how it is to be used, and having lots of brittle
else
Person.all + OtherPerson.all
end

An excellent post if I may say so that brings out the salient points I
think. Can the issues be summarised as follows?

  1. The controller should provide all the data that the view should
    display in instance variables (@person for example).
  2. The view is expected to understand the structure of the objects and
    so can access attributes (virtual or otherwise) of the objects.
  3. If the model needs to access the db in order to provide an
    attribute value, or accessing the attribute has some side effect that
    affects the db, then this is ok, providing the view does not ‘know’
    that the side effect or db access is happening. (Not very well written
    but I hope you know what I mean).
  4. The view must not call any method of the model who’s purpose is to
    perform an action rather than return a value.
  5. The view should not make any explicit use of model classes. For
    example there should be no reference to Person or any other model
    class

Colin

Huh :slight_smile:
Very nice debate and good conclusion. I think i should document it!

On Fri, Mar 12, 2010 at 11:35 PM, Josh C. [email protected]
wrote:

It saves 4 lines of code, but breaks one of the principles of MVC
def and end was worth it).


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On Fri, Mar 12, 2010 at 2:59 AM, Andy J.
[email protected]wrote:

clean.
It sounds like - when you start with “But” - that you disagree, but the
rest of your post seems to be arguing from the same side as my posts.

Cheers,

Yeah, I thought you were saying that not using a filter saves 4 lines of
code, and is therefore cleaner, and thus worth it. Seemed to be a weird
position to take, glad it was just a misunderstanding.

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