Ruby 模型的数组属性
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Array Attribute for Ruby Model
提问by tquarton
Is it possible to create an attribute for a class that is an array? I tried reading thisbut I didn't get much out of it. I want to do something like this:
是否可以为作为数组的类创建属性？我试着阅读这篇文章，但我没有从中得到太多。我想做这样的事情：
class CreateArches < ActiveRecord::Migration
def change
create_table :arches do |t|
t.string :name
t.array :thearray
t.timestamps
end
end
end
such that when I call .thearray on an instance of Arch I get an array that I can add new elements to.
这样当我在 Arch 实例上调用 .thearray 时，我会得到一个可以添加新元素的数组。
ruby-1.9.2-p290 :006 > arc = Arch.new
ruby-1.9.2-p290 :007 > arc.thearray
=> []
回答by sorens
Create a model with a text field
创建带有文本字段的模型
> rails g model Arches thearray:text
invoke active_record
create db/migrate/20111111174052_create_arches.rb
create app/models/arches.rb
invoke test_unit
create test/unit/arches_test.rb
create test/fixtures/arches.yml
> rake db:migrate
== CreateArches: migrating ===================================================
-- create_table(:arches)
-> 0.0012s
== CreateArches: migrated (0.0013s) ==========================================
edit your model to make the field serialized to an array
编辑您的模型以使字段序列化为数组
class Arches < ActiveRecord::Base
serialize :thearray,Array
end
test it out
测试一下
ruby-1.8.7-p299 :001 > a = Arches.new
=> #<Arches id: nil, thearray: [], created_at: nil, updated_at: nil>
ruby-1.8.7-p299 :002 > a.thearray
=> []
ruby-1.8.7-p299 :003 > a.thearray << "test"
=> ["test"]
回答by Marnen Laibow-Koser
While you can use a serialized array as tokland suggested, this is rarely a good idea in a relational database. You have three superior alternatives:
虽然您可以按照 tokland 的建议使用序列化数组，但这在关系数据库中很少是一个好主意。您有三个更好的选择：
- If the array holds entity objects, it's probably better modeled as a
has_manyrelationship. - If the array is really just an array of values such as numbers, then you might want to put each value in a separate field and use
composed_of. - If you're going to be using a lot of array values that aren't
has_manys, you might want to investigate a DB that actually supports array fields. PostgreSQL does this (and array fields are supported in Rails 4 migrations), but you might want to use either a non-SQL database like MongoDB or object persistence such as MagLevis supposed to provide.
- 如果数组包含实体对象，则最好将其建模为
has_many关系。 - 如果数组实际上只是一个值数组，例如数字，那么您可能希望将每个值放在一个单独的字段中并使用
composed_of. - 如果您要使用很多不是
has_manys的数组值，您可能需要调查一个实际支持数组字段的数据库。PostgreSQL 会这样做（Rails 4 迁移支持数组字段），但您可能想要使用非 SQL 数据库（如 MongoDB）或对象持久性（如MagLev应该提供）。
If you can describe your use case -- that is, what data you've got in the array -- we can try to help figure out what the best course of action is.
如果你能描述你的用例——也就是说，你在数组中得到了什么数据——我们可以尝试帮助找出最好的行动方案。
回答by tokland
Migration:
移民：
t.text :thearray, :default => [].to_yaml
In the model use serialize:
在模型中使用serialize：
class MyModel
serialize :thearray, Array
...
end
As Marnen says in his answer, it would be good to know what kind of info you want to store in that array, a serialized attribute may not be the best option.
正如 Marnen 在他的回答中所说，最好知道您想在该数组中存储什么样的信息，序列化属性可能不是最佳选择。
[Marten Veldthuis' warning] Be careful about changing the serialized array. If you change it directly like this:
[Marten Veldthuis 的警告] 更改序列化数组时要小心。如果你像这样直接改变它：
my_model.thearray = [1,2,3]
That works fine, but if you do this:
这工作正常，但如果你这样做：
my_model.thearray << 4
Then ActiveRecord won't detect that the value of thearray has changed. To tell AR about that change, you need to do this:
那么 ActiveRecord 不会检测到数组的值已经改变。要告诉 AR 有关该更改，您需要执行以下操作：
my_model.thearray_will_change!
my_model.thearray << 4
回答by akz92
If using Postgres, you can use its Array feature:
如果使用 Postgres，你可以使用它的Array 特性：
Migration:
移民：
add_column :model, :attribute, :text, array: true, default: []
And then just use it like an array:
然后像数组一样使用它：
model.attribute # []
model.attribute = ["d"] #["d"]
model.attribute << "e" # ["d", "e"]
This approach was mentioned by Marnen but I believe an example would be helpful here.
Marnen 提到了这种方法，但我相信这里有一个例子会有所帮助。
