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comp.lang.ruby

Accessing a YAML loaded object without the object's definition?

Steve Litt

9/29/2008 6:05:00 PM

Hi all,

In Ruby, I have a fairly complex nested object structure that I serialize to a
yaml file. Then, in another program, I read it into a varaible like this:

obj = YAML::load_file("myfile.yaml");

I can see all objects and names in obj within irb, but I can't access them
individually. For instance, in the original native that created the yaml,
there's this:

obj.customer.city

You cannot access that from the object read in with load_file. It creates an
error condition.

What DOES work is:

obj = Purchase.new(nil, nil)
obj = YAML::load_file("myfile.yaml");

puts obj.customer.city

That prints "Apopka".

A sample program is at the bottom of this email. As long as the classes are
defined in the program, they can be accessed. But if an object is created via
YAML::load_file(), I'm not able to access its data members.

Is there any way I can do it without including the class definition in the
code?

Thanks

SteveT

Steve Litt
Recession Relief Package
http://www.recession...

############ SAMPLE PROGRAM ###################
#!/usr/bin/ruby -w

require "yaml"

class Address
attr_accessor :street, :city, :state, :zip
def initialize(street, city, state, zip)
@street = street
@city = city
@state = state
@zip=zip
end
end

class Customer
attr_accessor :fname, :lname, :address
def initialize( fname, lname, address)
@fname = fname
@lname = lname
@address = address
end
end


class Item
attr_accessor :quantity, :priceper, :name
def initialize(name, quantity, priceper)
@name = name
@quantity = quantity
@priceper = priceper
end
end

class Purchase
attr_accessor :customer
attr_reader :amount
attr_accessor :date
attr_reader :items

def initialize(customer, date)
@customer = customer
@amount = amount
@date = date
@items = Array.new()
end
def additem(item)
@items.push(item)
end
def update_amount()
@amount = 0
@items.each do
|item|
@amount += (item.quantity.to_f * item.priceper.to_f)
end
end
end

#### MAIN ROUTINE
#### Load objects
address = Address.new(["121 Main Street", "Suite
201"], "Apopka", "FL", "33333");

customer = Customer.new("Steve", "Litt", address)

purchase = Purchase.new(customer, "3/3/2033")
purchase.additem(Item.new("Widget", 1, 1.00));
purchase.additem(Item.new("Gadget", 2, 2.00));
purchase.additem(Item.new("Left handed smoke bender", 3, 3.00));
purchase.update_amount()

#### Write out YAML to junk.yaml
ouf = File.new("./junk.yaml", "w");
ouf.write(YAML::dump(purchase))
ouf.close()

#### WRITE REPORT
#### Read YAML file and load into Purchase object p
p=Purchase.new(nil, nil)
p=YAML::load_file("./junk.yaml");

#### Date and total
printf "Purchase on %s, total cost $%0.2f\n", p.date, p.amount

#### Customer data
printf "\nCUSTOMER DATA:\n"
printf "%s %s\n", p.customer.fname, p.customer.lname
p.customer.address.street.each {|i| puts i}
printf "%s, %s, %s\n", p.customer.address.city, p.customer.address.state,
p.customer.address.zip

#### Items
printf "\nITEMS PURCHASED\n"
printf "%30s %10s %10s %10s\n", "ITEM NAME", "QUANTITY", "@", "TOTAL"
p.items.each do
|item|
printf "%30s %10d %10.2f %10.2f\n", item.name, item.quantity, item.priceper,
item.quantity * item.priceper

end
printf "%30s %10s %10s %10s\n", " ", " ", " ", "----------"
printf "%30s %10s %10s %10.2f\n", "TOTAL", " ", " ", p.amount

############ END OF SAMPLE PROGRAM ###################
2 Answers

Justin Collins

9/29/2008 8:24:00 PM

0

Steve Litt wrote:
> Hi all,
>
> In Ruby, I have a fairly complex nested object structure that I serialize to a
> yaml file. Then, in another program, I read it into a varaible like this:
>
> obj = YAML::load_file("myfile.yaml");
>
> I can see all objects and names in obj within irb, but I can't access them
> individually. For instance, in the original native that created the yaml,
> there's this:
>
> obj.customer.city
>
> You cannot access that from the object read in with load_file. It creates an
> error condition.
>
> What DOES work is:
>
> obj = Purchase.new(nil, nil)
>

That line is unnecessary (I tried your code and commented out that line,
worked fine.)

> obj = YAML::load_file("myfile.yaml");
>
> puts obj.customer.city
>
> That prints "Apopka".
>
> A sample program is at the bottom of this email. As long as the classes are
> defined in the program, they can be accessed. But if an object is created via
> YAML::load_file(), I'm not able to access its data members.
>
> Is there any way I can do it without including the class definition in the
> code?
>

Not really. It cannot generate the classes out of thin air and the YAML
files just store the name of the class. But you could put the class
definitions in separate files so they can be 'required' anywhere you
need them.

-Justin

Dejan Dimic

9/29/2008 8:32:00 PM

0

On Sep 29, 8:05 pm, Steve Litt <sl...@troubleshooters.com> wrote:
> Hi all,
>
> In Ruby, I have a fairly complex nested object structure that I serialize to a
> yaml file. Then, in another program, I read it into a varaible like this:
>
> obj = YAML::load_file("myfile.yaml");
>
> I can see all objects and names in obj within irb, but I can't access them
> individually. For instance, in the original native that created the yaml,
> there's this:
>
> obj.customer.city
>
> You cannot access that from the object read in with load_file. It creates an
> error condition.
>
> What DOES work is:
>
> obj = Purchase.new(nil, nil)
> obj = YAML::load_file("myfile.yaml");
>
> puts obj.customer.city
>
> That prints "Apopka".
>
> A sample program is at the bottom of this email. As long as the classes are
> defined in the program, they can be accessed. But if an object is created via
> YAML::load_file(), I'm not able to access its data members.
>
> Is there any way I can do it without including the class definition in the
> code?
>
> Thanks
>
> SteveT
>
> Steve Litt
> Recession Relief Packagehttp://www.recession...
>
> ############ SAMPLE PROGRAM ###################
> #!/usr/bin/ruby -w
>
> require "yaml"
>
> class Address
>         attr_accessor :street, :city, :state, :zip
>         def initialize(street, city, state, zip)
>                 @street = street
>                 @city = city
>                 @state = state
>                 @zip=zip
>         end
> end
>
> class Customer
>         attr_accessor :fname, :lname, :address
>         def initialize( fname, lname, address)
>                 @fname = fname
>                 @lname = lname
>                 @address = address
>         end
> end
>
> class Item
>         attr_accessor :quantity, :priceper, :name
>         def initialize(name, quantity, priceper)
>                 @name = name
>                 @quantity = quantity
>                 @priceper = priceper
>         end
> end
>
> class Purchase
>         attr_accessor :customer
>         attr_reader :amount
>         attr_accessor :date
>         attr_reader :items
>
>         def initialize(customer, date)
>                 @customer = customer
>                 @amount = amount
>                 @date = date
>                 @items = Array.new()
>         end
>         def additem(item)
>                 @items.push(item)
>         end
>         def update_amount()
>                 @amount = 0
>                 @items.each do
>                         |item|
>                         @amount += (item.quantity.to_f * item.priceper.to_f)
>                 end
>         end
> end
>
> #### MAIN ROUTINE
> #### Load objects
> address = Address.new(["121 Main Street", "Suite
> 201"], "Apopka", "FL", "33333");
>
> customer = Customer.new("Steve", "Litt", address)
>
> purchase = Purchase.new(customer, "3/3/2033")
> purchase.additem(Item.new("Widget", 1, 1.00));
> purchase.additem(Item.new("Gadget", 2, 2.00));
> purchase.additem(Item.new("Left handed smoke bender", 3, 3.00));
> purchase.update_amount()
>
> #### Write out YAML to junk.yaml
> ouf = File.new("./junk.yaml", "w");
> ouf.write(YAML::dump(purchase))
> ouf.close()
>
> #### WRITE REPORT
> #### Read YAML file and load into Purchase object p
> p=Purchase.new(nil, nil)
> p=YAML::load_file("./junk.yaml");
>
> #### Date and total
> printf "Purchase on %s, total cost $%0.2f\n", p.date, p.amount
>
> #### Customer data
> printf "\nCUSTOMER DATA:\n"
> printf "%s %s\n", p.customer.fname, p.customer.lname
> p.customer.address.street.each {|i| puts i}
> printf "%s, %s, %s\n", p.customer.address.city, p.customer.address.state,
> p.customer.address.zip
>
> #### Items
> printf "\nITEMS PURCHASED\n"
> printf "%30s %10s %10s %10s\n", "ITEM NAME", "QUANTITY", "@", "TOTAL"
> p.items.each do
>         |item|
>         printf "%30s %10d %10.2f %10.2f\n", item.name, item.quantity, item.priceper,
> item.quantity * item.priceper
>
> end
> printf "%30s %10s %10s %10s\n", " ", " ", " ", "----------"
> printf "%30s %10s %10s %10.2f\n", "TOTAL", " ", " ", p.amount
>
> ############ END OF SAMPLE PROGRAM ###################

take look at: http://yaml4r.sourceforge.net/doc/page/type_fa...