Mass Assignment on Clas

[Pete Moran]

Hi there,

I am a total newbie to Ruby, so please bare with me.

I want to be able to be able to initialise a Class with a hash. For
instance If I have the class

class Vehicle
attr_accessor :vtype, :description, :vehicle, :capacity
end

I want to be able to do

Vehicle.newvtype => 'ECAR', :description => 'Great Car', :vehicle =>
'Ford Focus', :capacity => '10');

Now I could do something like

def initialize(items)
@vtype = items[:vtype]
@description = items[:description]
@vehicle = items[:vehicle]
@capacity = items[:capacity]
# puts items.inspect
end

But I was wondering if there was a more generic way of doing this
without specifically defining each variable in initialize? I think
ActiveRecord does something similar!

Many thanks for your assist!

 

[David A. Black]

Hi --

Hi there,

I am a total newbie to Ruby, so please bare with me.

I want to be able to be able to initialise a Class with a hash. For
instance If I have the class

class Vehicle
attr_accessor :vtype, :description, :vehicle, :capacity
end

I want to be able to do

Vehicle.newvtype => 'ECAR', :description => 'Great Car', :vehicle =>
'Ford Focus', :capacity => '10');

Now I could do something like

def initialize(items)
@vtype = items[:vtype]
@description = items[:description]
@vehicle = items[:vehicle]
@capacity = items[:capacity]
# puts items.inspect
end

But I was wondering if there was a more generic way of doing this
without specifically defining each variable in initialize? I think
ActiveRecord does something similar!

How about:

def initialize(items)
items.each do |key,value|
instance_variable_set("@#{key}", value)
end
end

(possible with some checking to make sure they're what you want).


David

--
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Q: What's the best way to get a really solid knowledge of Ruby?
A: Come to our Ruby training in Edison, New Jersey, September 14-17!
Instructors: David A. Black and Erik Kastner
More info and registration: http://rubyurl.com/vmzN

 

[7stud --]

Hi there,

I am a total newbie to Ruby, so please bare with me.

I want to be able to be able to initialise a Class with a hash. For
instance If I have the class

class Vehicle
attr_accessor :vtype, :description, :vehicle, :capacity
end

I want to be able to do

Vehicle.newvtype => 'ECAR', :description => 'Great Car', :vehicle =>
'Ford Focus', :capacity => '10');

Now I could do something like

def initialize(items)
@vtype = items[:vtype]
@description = items[:description]
@vehicle = items[:vehicle]
@capacity = items[:capacity]
# puts items.inspect
end

But I was wondering if there was a more generic way of doing this
without specifically defining each variable in initialize? I think
ActiveRecord does something similar!

Many thanks for your assist!

class X

attr_reader :vtype, :description

def initialize(items)
self.vtype = items[:vtype]
self.description = items[:description]
end

def vtype=(val)
if ["Ecar", "Fcar", "Gcar"].include? val
@vtype = val
else
puts "Error"
@vtype = nil
end
end

def description=(descr)
if descr.length > 20
puts "Error"
else
@description = descr
end
end
end

x = X.newvtype => "Ecar", :description => "Great Car")
puts x.vtype
puts x.description

 

[Rick DeNatale]

I am a total newbie to Ruby, so please bare with me.

Averting my eyes, I'd prefer to keep my clothes on myself! In other
words I'll grin and BEAR it! <G>

Seriously, David Black already gave you pretty much the response I
would have, although my first steps in refining it a bit might be to
make the hash arg optional:

def initialize(items={}
items.each do |key,value|
instance_variable_set("@#{key}", value)
end
end

Another thing variation would be to use those accessors so as to not
add 'accidental' instance variables

def initialize(items={}
items.each do |key,value|
send("#{key}=", value) rescue raise "unknown attribute #{key}"
end
end

And as the King of Siam said, etcetera, etcetera, etcetera!

--
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

 

[Rick DeNatale]

Another thing variation would be to use those accessors so as to not
add 'accidental' instance variables

Why do I always see typos just AFTER I hit send????? s/thing //

--
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

 

[David A. Black]

Hi --

Why do I always see typos just AFTER I hit send????? s/thing //

Run your code through Ruby and you'll see another


David

--
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Q: What's the best way to get a really solid knowledge of Ruby?
A: Come to our Ruby training in Edison, New Jersey, September 14-17!
Instructors: David A. Black and Erik Kastner
More info and registration: http://rubyurl.com/vmzN

 

[Rick DeNatale]

Hi --



Run your code through Ruby and you'll see another

Actually two.

Balancing parentheses is the hobgoblin of little minds! <G>


--=20
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale

 

[Pete Moran]

Hi --



Run your code through Ruby and you'll see another


David

Thanks for your responses - much appreciated!

Is this the David A. Black who wrote Ruby for Rails? if so wow a real
honour! I recently finished your book (and enjoyed it).

Coming from a Perl backgrounds its been interesting getting up to speed
with Ruby/Rails although I think I am just at the beginning of the
journey.. so much to learn!

 

[7stud --]

Is this the David A. Black who wrote Ruby for Rails? if so wow a real
honour! I recently finished your book (and enjoyed it).

Yes, as well as the recently published "The Well Grounded Rubyist".

 

[David A. Black]

Hi --

Thanks for your responses - much appreciated!

Is this the David A. Black who wrote Ruby for Rails? if so wow a real
honour! I recently finished your book (and enjoyed it).

The hono(u)r is all mine I'm glad you liked the book. It has been,
to use the only word I've been able to think of to describe the
process, "repurposed" into a just-Ruby book, The Well-Grounded
Rubyist, which you might also like.

Coming from a Perl backgrounds its been interesting getting up to speed
with Ruby/Rails although I think I am just at the beginning of the
journey.. so much to learn!

I'm not at the beginning of the journey but after the beginning it's
all middle -- so I'm somewhere in the middle, and enjoying it greatly.


David

--
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Ruby/Rails training, mentoring, consulting, code-review
Latest book: The Well-Grounded Rubyist (http://www.manning.com/black2)

September Ruby training in NJ has been POSTPONED. Details to follow.

 

[Gordon Thiesfeld]

Hi there,

I am a total newbie to Ruby, so please bare with me.

I want to be able to be able to initialise a Class with a hash. =A0For
instance If I have the class

class Vehicle
=A0attr_accessor :vtype, :description, :vehicle, :capacity
end

I want to be able to do

Vehicle.newvtype =3D> 'ECAR', :description =3D> 'Great Car', :vehicle = =3D>
'Ford Focus', :capacity =3D> '10');

Now I could do something like

def initialize(items)
=A0 =A0 @vtype =3D items[:vtype]
=A0 =A0 @description =3D items[:description]
=A0 =A0 @vehicle =3D items[:vehicle]
=A0 =A0 @capacity =3D items[:capacity]
# =A0 =A0 puts items.inspect
=A0 end

But I was wondering if there was a more generic way of doing this
without specifically defining each variable in initialize? I think
ActiveRecord does something similar!

Many thanks for your assist!

Just playing devil's advocate, what about using OpenStruct?

require 'ostruct'

class Vehicle < OpenStruct

end

v1 =3D Vehicle.newvtype =3D> 'ECAR', :description =3D> 'Great Car', :vehi=
cle =3D>
'Ford Focus', :capacity =3D> '10')

I guess the concern would be the possibility of adding additional
accessors. Using attr_accessor inside the class seems to keep me from
updating the variables.