Rails 5.2 cache key for relations generating two queries









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I have a view using fragment caching for an ActiveRecord relation, e.g.



<% cache MyModel.all do %>
...
<% end %>


I see two DB queries generated in this case



  1. SELECT COUNT(*) AS "size", MAX("my_model"."updated_at") AS timestamp FROM "my_model"

  2. SELECT "my_model".* from "my_model"

I expect the first one, and it's usually a much more efficient query. I did not expect the second one.



If I instead use:



<% cache ActiveSupport::Cache.expand_cache_key(MyModel.all) do %>
...
<% end %>


then I get only the first query with the same resulting cache key.



Is it a bug or am I doing something wrong?



EDIT: narrowed down to where this happens: see https://github.com/rails/rails/pull/29092#issuecomment-437572543




when
normalize_version
is executed, the relation does not respond to cache_version, and
therefore ends up being expanded with
to_a.
So essentially, calling Product.all.to_a and then for each object
calling cache_version, which returns nil.







ruby-on-rails caching activerecord activesupport







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    up vote
    1
    down vote

    favorite












    I have a view using fragment caching for an ActiveRecord relation, e.g.



    <% cache MyModel.all do %>
    ...
    <% end %>


    I see two DB queries generated in this case



    1. SELECT COUNT(*) AS "size", MAX("my_model"."updated_at") AS timestamp FROM "my_model"

    2. SELECT "my_model".* from "my_model"

    I expect the first one, and it's usually a much more efficient query. I did not expect the second one.



    If I instead use:



    <% cache ActiveSupport::Cache.expand_cache_key(MyModel.all) do %>
    ...
    <% end %>


    then I get only the first query with the same resulting cache key.



    Is it a bug or am I doing something wrong?



    EDIT: narrowed down to where this happens: see https://github.com/rails/rails/pull/29092#issuecomment-437572543




    when
    normalize_version
    is executed, the relation does not respond to cache_version, and
    therefore ends up being expanded with
    to_a.
    So essentially, calling Product.all.to_a and then for each object
    calling cache_version, which returns nil.







    ruby-on-rails caching activerecord activesupport







    share|improve this question

























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      I have a view using fragment caching for an ActiveRecord relation, e.g.



      <% cache MyModel.all do %>
      ...
      <% end %>


      I see two DB queries generated in this case



      1. SELECT COUNT(*) AS "size", MAX("my_model"."updated_at") AS timestamp FROM "my_model"

      2. SELECT "my_model".* from "my_model"

      I expect the first one, and it's usually a much more efficient query. I did not expect the second one.



      If I instead use:



      <% cache ActiveSupport::Cache.expand_cache_key(MyModel.all) do %>
      ...
      <% end %>


      then I get only the first query with the same resulting cache key.



      Is it a bug or am I doing something wrong?



      EDIT: narrowed down to where this happens: see https://github.com/rails/rails/pull/29092#issuecomment-437572543




      when
      normalize_version
      is executed, the relation does not respond to cache_version, and
      therefore ends up being expanded with
      to_a.
      So essentially, calling Product.all.to_a and then for each object
      calling cache_version, which returns nil.







      ruby-on-rails caching activerecord activesupport







      share|improve this question















      I have a view using fragment caching for an ActiveRecord relation, e.g.



      <% cache MyModel.all do %>
      ...
      <% end %>


      I see two DB queries generated in this case



      1. SELECT COUNT(*) AS "size", MAX("my_model"."updated_at") AS timestamp FROM "my_model"

      2. SELECT "my_model".* from "my_model"

      I expect the first one, and it's usually a much more efficient query. I did not expect the second one.



      If I instead use:



      <% cache ActiveSupport::Cache.expand_cache_key(MyModel.all) do %>
      ...
      <% end %>


      then I get only the first query with the same resulting cache key.



      Is it a bug or am I doing something wrong?



      EDIT: narrowed down to where this happens: see https://github.com/rails/rails/pull/29092#issuecomment-437572543




      when
      normalize_version
      is executed, the relation does not respond to cache_version, and
      therefore ends up being expanded with
      to_a.
      So essentially, calling Product.all.to_a and then for each object
      calling cache_version, which returns nil.







      ruby-on-rails caching activerecord activesupport




      ruby-on-rails caching activerecord activesupport






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 days ago

























      asked Nov 9 at 8:59









      gingerlime

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