Enable query cache if set a configurations

ActiveRecord query cache is available when a connection is connected.
Therefore, query cache is unavailable when entering the ActiveRecord::Base.cache block without being connected.

```ruby
ActiveRecord::Base.cache do
  Task.find(1) # access to database.
  Task.find(1) # access to database. unavailable query cache
end
```

If we use query cache with batch script etc, we need to connect before that.
```ruby
Task.connection

ActiveRecord::Base.cache do
  Task.find(1) # access to database.
  Task.find(1) # available query cache
end
```

Before version 3.1, query cache had been enabled if a configuration was set up.
In order to solve the `DATABASE_URL` issue(#8074), ActiveRecord has checked whether a connection is connected or not.

Today, ActiveRecord.configurations respect `DATABASE_URL`.
https://github.com/rails/rails/blob/master/activerecord/lib/active_record/core.rb#L46

1 files changed, 6 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index ec246e97bc..e4c2e1f86f 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -5,20 +5,20 @@ module ActiveRecord
       # Enable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def cache(&block)
-        if connected?
-          connection.cache(&block)
-        else
+        if configurations.empty?
           yield
+        else
+          connection.cache(&block)
         end
       end
 
       # Disable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def uncached(&block)
-        if connected?
-          connection.uncached(&block)
-        else
+        if configurations.empty?
           yield
+        else
+          connection.uncached(&block)
         end
       end
     end