Re: [Rails] Re: Why joins queries make result readonly?

On 14 May 2013 11:12, Frederick Cheung <frederick.cheung@gmail.com> wrote:
>
>
> On Tuesday, May 14, 2013 10:26:56 AM UTC+1, Илья Воронцов wrote:
>>
>> Are there any rationalies to make queries obtained by joining scope to be
>> readonly? I read some old posts (pre-rails3) that joins adds additional
>> columns to record so that ActiveRecord doesn't know how to update that
>> fields, but actually I don't see that fields. For example I write model
>> class Order < ActiveRecord::Base
>> has_and_belongs_to_many :executors, class_name: 'Specialist',
>> join_table: 'order_executors'
>> scope :by_executor, ->(executor_id) {
>> joins(:executors).where(specialists: {id: executor_id} ) }
>> end
>>
>> and make query Order.by_executor(1) so that I get:
>>
>> Order Load (2.0ms) SELECT "orders".* FROM "orders" INNER JOIN
>> "order_executors" ON "order_executors"."order_id" = "orders"."id" INNER JOIN
>> "specialists" ON "specialists"."id" = "order_executors"."specialist_id"
>> WHERE "specialists"."id" = 1
>> => [#<Order id: 20, orderable_id: 11, orderable_type: "PlanDevelopment",
>> client_id: 1, completion_status: "finished", created_at: "2013-05-13
>> 20:48:19", updated_at: "2013-05-14 00:36:38", price:
>> #<BigDecimal:67e5898,'0.14E2',9(36)>>]
>>
>> I see no additional columns but Order.by_executor(1).first.readonly? is
>> true. Is that necessary?
>>
>> p.s. Yes I know that I can set readonly(false) or explicitly specify
>> select clause - so that records won't become readonly. But I want to
>> understand why this blocking behavior is necessary (if it is still true) and
>> what damage will be possible without readonly mark? Also I don't understand,
>> how can I shot myself if I explicitly set readonly(false).
>
>
> This might be a hangover from the past - I think active record didn't use to
> default to orders.* - the default select clause was select *.
>
> The danger is only if you do select columns from the other tables. This can
> either prevent saves (because your object has an attribute that doesn't
> exist for the model) or mask existing data, eg if both of the joined tables
> have a client_id column and you do select * then the activerecord object
> will have a single client_id attribute that has only one of those values.

Should the OP be using includes rather than joins?

Colin

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