Rails模型中的实例变量 [英] Instance Variables in a Rails Model
问题描述
我有这个变量意见,我想将其作为实例变量存储在模型中...我是对的,假设我需要为其添加列,否则将不断对其进行重新计算吗?
I have this variable opinions I want to store as an instance variable in my model... am I right in assuming I will need to add a column for it or else be re-calculating it constantly?
我的另一个问题是,存储到列变量而不是本地变量中的语法是什么?
My other question is what is the syntax to store into a column variable instead of just a local one?
感谢您的帮助,代码如下:
Thanks for the help, code below:
# == Schema Information
#
# Table name: simulations
#
# id :integer not null, primary key
# x_size :integer
# y_size :integer
# verdict :string
# arrangement :string
# user_id :integer
#
class Simulation < ActiveRecord::Base
belongs_to :user
serialize :arrangement, Array
validates :user_id, presence: true
validates :x_size, :y_size, presence: true, :numericality => {:only_integer => true}
validates_numericality_of :x_size, :y_size, :greater_than => 0
def self.keys
[:soft, :hard, :none]
end
def generate_arrangement
@opinions = Hash[ Simulation.keys.map { |key| [key, 0] } ]
@arrangement = Array.new(y_size) { Array.new(x_size) }
@arrangement.each_with_index do |row, y_index|
row.each_with_index do |current, x_index|
rand_opinion = Simulation.keys[rand(0..2)]
@arrangement[y_index][x_index] = rand_opinion
@opinions[rand_opinion] += 1
end
end
end
def verdict
if @opinions[:hard] > @opinions[:soft]
:hard
elsif @opinions[:soft] > @opinions[:hard]
:soft
else
:push
end
end
def state
@arrangement
end
def next
new_arrangement = Array.new(@arrangement.size) { |array| array = Array.new(@arrangement.first.size) }
@opinions = Hash[ Simulation.keys.map { |key| [key, 0] } ]
@seating_arrangement.each_with_index do |array, y_index|
array.each_with_index do |opinion, x_index|
new_arrangement[y_index][x_index] = update_opinion_for x_index, y_index
@opinions[new_arrangement[y_index][x_index]] += 1
end
end
@arrangement = new_arrangement
end
private
def in_array_range?(x, y)
((x >= 0) and (y >= 0) and (x < @arrangement[0].size) and (y < @arrangement.size))
end
def update_opinion_for(x, y)
local_opinions = Hash[ Simulation.keys.map { |key| [key, 0] } ]
for y_pos in (y-1)..(y+1)
for x_pos in (x-1)..(x+1)
if in_array_range? x_pos, y_pos and not(x == x_pos and y == y_pos)
local_opinions[@arrangement[y_pos][x_pos]] += 1
end
end
end
opinion = @arrangement[y][x]
opinionated_neighbours_count = local_opinions[:hard] + local_opinions[:soft]
if (opinion != :none) and (opinionated_neighbours_count < 2 or opinionated_neighbours_count > 3)
opinion = :none
elsif opinion == :none and opinionated_neighbours_count == 3
if local_opinions[:hard] > local_opinions[:soft]
opinion = :hard
elsif local_opinions[:soft] > local_opinions[:hard]
opinion = :soft
end
end
opinion
end
end
推荐答案
ActiveRecord分析数据库表并通过元编程创建setter和getter方法.
ActiveRecord analyzes the database tables and creates setter and getter methods with metaprogramming.
因此,您将创建一个带有迁移的数据库列:
So you would create a database column with a migration:
rails g migration AddOpinionToSimulation opinion:hash
请注意,并非所有数据库都支持在列中存储哈希或类似的键/值数据类型. Postgres做到了.如果您需要使用另一个数据库(例如MySQL),则应考虑使用一种关系(将数据存储在另一个表中).
Note that not all databases support storing a hash or a similar key/value data type in a column. Postgres does. If you need to use another database such MySQL you should consider using a relation instead (storing the data in another table).
然后,当您访问simulation.opinion
时,它将自动获取数据库列的值(如果记录是持久的).
Then when you access simulation.opinion
it will automatically get the database column value (if the record is persisted).
由于ActiveRecord创建了一个setter和getter,因此您可以通过以下方式从模型内访问属性:
Since ActiveRecord creates a setter and getter you can access your property from within the Model as:
class Simulation < ActiveRecord::Base
# ...
def an_example_method
self.opinions # getter method
# since self is the implied receiver you can simply do
opinions
opinions = {foo: "bar"} # setter method.
end
end
使用普通红宝石attr_accessor
,attr_reader
和attr_writer
宏时也是如此.
The same applies when using the plain ruby attr_accessor
, attr_reader
and attr_writer
macros.
当您分配由数据库列支持的属性时,ActiveRecord将该属性标记为 dirty ,并在保存记录时将其包括在内.
When you assign to an attribute backed by a database column ActiveRecord marks the attribute as dirty and will include it when you save the record.
ActiveRecord有一些直接更新属性的方法:update
,update_attributes
和update_attribute
.呼叫签名及其处理回调的方式有所不同.
ActiveRecord has a few methods to directly update attributes: update
, update_attributes
and update_attribute
. There are differences in the call signature and how they handle callbacks.
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