I have an attribute coming back from Active Record that is a Big Decimal. The database column's data is numeric(18,0) and I'm not authorized to change it. i would like to be able to convert the attribute into an Integer with no decimal precision, but i'm not having any luck. I know that I can convert the value into something else by using big_decimal.to_i, however I am hoping there is a way to handle this within the Active Record Model possibly after_initialize so that I don't have to worry about conversion anywhere else in my code. Any help would be appreciated, thanks.
If you're stuck with a legacy schema you can always work around that by adding a wrapper method:
class MyModel < ActiveRecord::Base
def int_column
value = read_attribute(:big_decimal)
# Preserve `nil` values and avoid converting to zero.
value and value.to_i
end
def int_column=(value)
write_attribute(:big_decimal, value)
end
end
That gives you a method for reading/writing from that column using an alternate name.
You can always alias the current method and then override it.
Let's say the attribute is charge
class Transaction < ActiveRecord::Base
# right now #charge returns #<BigDecimal:7fb6c285fe28,'0.0',9(18)>
# now we can alias the current method #charge
alias_method :big_decimal_charge, :charge
# now they both return #<BigDecimal:7fb6c285fe28,'0.0',9(18)>
# and we can redefine #charge, based on the alias
def charge
big_decimal_charge.to_i
end
end
I wouldn't imagine there would be a need to change the setter.
Related
In my rails model I have a JSON column which stores some meta information.
This is to be entered bu the user from a form.
Since the keys of the JSON column are not attributes of the model I cannot use them directly in form_for instead I need to define a virtual attribute.
Since this number of virtual attributes could grow to be arbitrarily lengthy I would like to use meta programming to define the attributes.
I did try the answer in this question however when I use the constant in my model I get an error saying that the constant is undefined. So I added the symbols for the keys in an array directly and iterate over them in the module. When I do this I get an error that says stack level too deep.
Please can someone help me out here?
If you are using PostgreSQL specific columns like hstore or json simply use store_accessor instead to generate the accessor methods. Be aware that these columns use a string keyed hash and do not allow access using a symbol.
class Model < ActiveRecord::Base
store_accessor :my_json_column, [ :key_1, :key_2, key_3 ]
end
What it doing under the hood? It has define write\read helper methods:
def store_accessor(store_attribute, *keys)
keys = keys.flatten
_store_accessors_module.module_eval do
keys.each do |key|
define_method("#{key}=") do |value|
write_store_attribute(store_attribute, key, value)
end
define_method(key) do
read_store_attribute(store_attribute, key)
end
end
end
# .....
store
I figured it out. I return the attribute as a key of the JSON column and it works fine now.
# lib/virtuals.rb
module Virtuals
%W(key_1 key_2 key_3).each do |attr|
define_method(attr) do
self.my_json_column[attr]
end
define_method("#{attr}=") do |val|
self.my_json_column[attr] = val
end
end
end
In my Model i just need to include that above module and it works fine in the form_for and updates correctly as well.
Is it possible to specify the column for an attribute? I have something like:
NAME, COUNTRY
The database is quite large and I have over a thousand columns which are capitalized like this. I want to refer to them as so:
attr_accessible :name, :country
Where :name = column NAME. I'd prefer Model.name rather than Model.NAME. It isn't possible to downcase every column name in the structure file.
Here is an idea to do the way you preferred.
Command to generate migration: (In my example, im applying this on Posts table. Change according to your table name)
rails g migrate RenameColumnsOfPosts
Below is the migration up method. Here taking all the column names and for each one I'm applying rename_column to make it downcase.
class RenameColumnsOfPosts < ActiveRecord::Migration
def up
Post.columns.map(&:name).each do |column_name|
rename_column(:posts, column_name, column_name.downcase)
end
end
def down
#You can do the opposite operation here. Leaving on you
end
end
As i didnt run it personally, it might need some changes. So start with it and let me know if facing any problem.
Please write code inside of model ,
it's just for demostration code,after you get it and update as per logic :
This Code inside of model :
...
attr_accessor :name,:country
before_save :fill_save
..
#assign variable like ...
def fill_save
self.NAME= self.name
self.COUNTRY= self.country
end
....
I have a SchoolDay class that represents a school day: it can tell you the date, the semester, the term, the week, and the day. It can generate a string like "Sem1 13A Fri". To store these objects in the database, I want them serialized as a string.
Here is my DataMapper custom type code. I've sort of scraped ideas from the code in dm-types because (disappointingly) there is no real documentation for creating custom types. Sorry it's long.
module DataMapper
class Property
class SchoolDay < DataMapper::Property::String
#load_as ::SchoolRecord::DomainObjects::SchoolDay
# Commented out: the 'load_as' method is not found
def load(value)
# Take a string from the database and load it. We need a calendar!
val = case value
when ::String then calendar.schoolday(value)
when ::SR::DO::SchoolDay then value
else
# fail
end
end
def dump(value)
# Store a SchoolDay value into the database as a string.
case value
when SR::DO::SchoolDay
sd = value
"Sem#{sd.semester} #{sd.weekstr} #{sd.day}"
when ::String
value
else
# fail
end
end
def typecast(value)
# I don't know what this is supposed to do -- that is, when and why it
# is called -- but I am aping the behaviour of the Regexp custom type,
# which, like this one, stores as a String and loads as something else.
load(value)
end
# private methods calendar() and error_message() omitted
end
end
end
This code works for reading from the (SQLite) database, but not for creating new rows. The error message is:
Schoolday must be of type String
The code that defines the DataMapper resource and tries to create the record is:
class LessonDescription
include DataMapper::Resource
property :id, Serial
property :schoolday, SchoolDay # "Sem1 3A Fri"
property :class_label, String # "10"
property :period, Integer # (0..6), 0 being before school
property :description, Text # "Completed yesterday's worksheet. hw:(4-07)"
end
# ...
ld = LessonDescription.create(
schoolday: #schoolday,
class_label: #class_label,
period: #period,
description: description
)
Here is the code for the Regexp datamapper type in the dm-types library. It's so simple!
module DataMapper
class Property
class Regexp < String
load_as ::Regexp # NOTE THIS LINE
def load(value)
::Regexp.new(value) unless value.nil?
end
def dump(value)
value.source unless value.nil?
end
def typecast(value)
load(value)
end
end
end
end
For some reason, I cannot use the load_as line in my code.
To summarise: I am trying to create a custom type that translates between a SchoolDay (domain object) and a String (database representation). The translation is easy, and I've copied the code structure primarily from the DataMapper Regexp type. But when I try to save a SchoolDay, it complains that I'm not giving it a string. Frustratingly, I can't use the "load_as" method that the built-in and custom types all use, even though I have the latest gem. I can't find the "load_as" method defined anywhere in the source code for DataMapper, either. But it's called!
Sorry for the ridiculous length. Any help would be greatly appreciated, as would a pointer to a guide for creating these things that I have somehow missed.
It seems that the current code of dm-types at github hasn't made it to any official release -- that's why load_as doesn't work in your example. But try to add this method:
module DataMapper
class Property
class SchoolDay < DataMapper::Property::String
def custom?
true
end
end
end
end
That's working here.
I've been following this article to display ActiveRecord data in QtRuby. I've copied the BoatTableModel class from there(used my own code for the rest). In the article, BoatTableModel is defined to only support the Boat model, but except for the column definitions the code is quite generic. So, I've changed it so instead of having the columns defined there, I've made it take the columns from a column_names method, and define that methods in subclasses for each model.
Here is my code:
class QtArModel<Qt::AbstractTableModel
def initialize(items)
super()
#items=items
end
def rowCount(parent=nil)
#items.size
end
def columnCount(parent=nil)
column_names.length
end
def data(index,role=Qt::DisplayRole)
invalid=Qt::Variant.new
return invalid unless role==Qt::DisplayRole or role==Qt::EditRole
item=#items[index.row]
return invalid if item.nil?
v=item[column_names[index.column]]||""
return Qt::Variant.new(v)
end
def headerData(section,orientation,role=Qt::DisplayRole)
invalid=Qt::Variant.new
return invalid unless role==Qt::DisplayRole
v=case orientation
when Qt::Horizontal
column_names[section]
else
""
end
return Qt::Variant.new(v.to_s)
end
def flags(index)
return Qt::ItemIsEditable|super(index)
end
def setData(index,variant,role=Qt::EditRole)
if index.valid? and role==Qt::EditRole
s=variant.toString
item=#items[index.row]
if index.column.between?(0,column_names.length-1)
item[column_names[index.column]]=s
else
raise "invalid column #{index.column}"
end
item.save
emit dataChanged(index,index)
else
return false
end
end
end
class QtCoursesTableModel<QtArModel
def column_names
return [
:number,
:name,
:tutor_name,
:site,
:active,
]
end
end
class QtTasksTableModel<QtArModel
def column_names
return [
:course,
:ex_number,
:received,
:due,
:description,
:link,
:completed,
:file,
]
end
end
Now, when I display one model(doesn't matter which) - everything works just fine. However, when I display both models, each in it's own Qt::TableView - only the first one is displayed, and the other table view is blank.
I've tried different ordering, and the table that gets to display it's data is always the one which it's Qt::TableView is created first - the order of the creating the Qt models does not matter. Also, when I create the model object for the first table, but don't actually set it's model property to it, the second table displays it's data.
I've also tried to display the same model twice in two different table views - and it worked - for a split second, and then the second view's data disappeared.
I've also tried to copy-paste the QtArModel, change it's name, and make one of the models inherit from the copy. That did work - but it's obviously a huge code duplication, so I would really like to avoid that.
Now, my guess is that something in QtArModel is defined as a class member instead of instance member, making both model instances share something they shouldn't share. It has to be in QtArModel - because if it was higher in the inheritance tree, the problem would have remained when I've duplicated QtArModel. However, I can't find anything in my QtArModel that's class-scoped instead of instance-scoped.
What am I missing?
OK, I've managed to work this out. Apparently, the problem was not the inheritance, but the GC. Since the only connection to the models was from TableView's model property - which is just a wrapper for C++ getter and setter - ruby thought it lost the reference to my models, and GC'd them.
Solved by keeping the models in ruby variables.
I was following the guide from the DataMapper site, and this is what I have:
module DataMapper
class Property
class SymbolStore < String
def dump(v)
v.to_s
end
def load(v)
v.to_sym
end
def typcast_to_primitive(v)
v.to_s
end
end
end
end
But, I'm getting strange behaviour. When I try to set a value that is a SymbolStore, it comes back as a string. However, if I load a record, it comes back properly, as a symbol. From my experiments, load only seems to be called when a record is loaded, and not when I'm trying to get the value of something I've just set.
In the real world, I should not need to get a value I have just set, but this problem does not make sense.
Try it with typecast_to_primitive (you had a typo).