assume arg to Account.invalidate_cache is relative to current shard

instead of assuming it's relative to the birth shard

Note: this means that the call to invalidate the cache before an account
is saved should start working, which may increase the number of cache
invalidations on this key.

fixes CNVS-25290

test plan:
- in a rails console, activate a shard that is not the birth shard
- Call `Account.find_cached(<local_id>)`, notice the db query
- Call `Account.invalidate_cache(<local_id>)`, should return true or
  1 indicating that it successfully deleted something from the cache

Change-Id: I1da7a6ab4eb457d9bc4287f2294aebcb2f9c825e
Reviewed-on: https://gerrit.instructure.com/67732
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Reviewed-by: Jacob Fugal <jacob@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>

Author: simonista

app/models/account.rb

@@ -525,8 +525,10 @@ def self.account_lookup_cache_key(id)
   end
 
   def self.invalidate_cache(id)
+    return unless id
+    birth_id = Shard.relative_id_for(id, Shard.current, Shard.birth)
     Shard.birth.activate do
-      Rails.cache.delete(account_lookup_cache_key(id)) if id
+      Rails.cache.delete(account_lookup_cache_key(birth_id)) if birth_id
     end
   rescue
     nil

spec/models/account_spec.rb

@@ -20,17 +20,6 @@
 
 describe Account do
 
-  describe ".find_cached" do
-    specs_require_sharding
-
-    it "works relative to a different shard" do
-      @shard1.activate do
-        a = Account.create!
-        expect(Account.find_cached(a.id)).to eq a
-      end
-    end
-  end
-
   it "should provide a list of courses" do
     expect{ Account.new.courses }.not_to raise_error
   end
@@ -1407,4 +1396,30 @@ def account_with_admin_and_restricted_user(account, restricted_role)
       end
     end
   end
+
+  context "account cache" do
+    specs_require_sharding
+
+    describe ".find_cached" do
+      it "works relative to a different shard" do
+        @shard1.activate do
+          a = Account.create!
+          expect(Account.find_cached(a.id)).to eq a
+        end
+      end
+    end
+
+    describe ".invalidate_cache" do
+      it "works relative to a different shard" do
+        enable_cache do
+          @shard1.activate do
+            a = Account.create!
+            Account.find_cached(a.id) # set the cache
+            expect(Account.invalidate_cache(a.id)).to eq true
+          end
+        end
+      end
+    end
+  end
+
 end