Only refresh concurrently if view is populated

This implementation will still error if you ask for a concurrent refresh
of a non-populated view if your database does not support concurrent
refreshes. I'm happy with this because the user has asked for a thing
that we know cannot succeed, even under the right circumstances, and we
should tell them that., and we should tell them that.

Co-authored-by: Derek Prior <[email protected]>
Co-authored-by: Caleb Hearth <[email protected]>

lib/scenic/adapters/postgres.rb

@@ -14,7 +14,7 @@ module Scenic
   module Adapters
     # An adapter for managing Postgres views.
     #
-    # These methods are used interally by Scenic and are not intended for direct
+    # These methods are used internally by Scenic and are not intended for direct
     # use. Methods that alter database schema are intended to be called via
     # {Statements}, while {#refresh_materialized_view} is called via
     # {Scenic.database}.
@@ -124,7 +124,7 @@ def drop_view(name)
       # @param sql_definition The SQL schema that defines the materialized view.
       # @param no_data [Boolean] Default: false. Set to true to create
       #   materialized view without running the associated query. You will need
-      #   to perform a non-concurrent refresh to populate with data.
+      #   to perform a refresh to populate with data.
       #
       # This is typically called in a migration via {Statements#create_view}.
       #
@@ -154,7 +154,7 @@ def create_materialized_view(name, sql_definition, no_data: false)
       # @param sql_definition The SQL schema for the updated view.
       # @param no_data [Boolean] Default: false. Set to true to create
       #   materialized view without running the associated query. You will need
-      #   to perform a non-concurrent refresh to populate with data.
+      #   to perform a refresh to populate with data.
       #
       # @raise [MaterializedViewsNotSupportedError] if the version of Postgres
       #   in use does not support materialized views.
@@ -193,7 +193,10 @@ def drop_materialized_view(name)
       #   refreshed without locking the view for select but requires that the
       #   table have at least one unique index that covers all rows. Attempts to
       #   refresh concurrently without a unique index will raise a descriptive
-      #   error.
+      #   error. This option is ignored if the view is not populated, as it
+      #   would cause an error to be raised by Postgres. Default: false.
+      # @param cascade [Boolean] Whether to refresh dependent materialized
+      #   views. Default: false.
       #
       # @raise [MaterializedViewsNotSupportedError] if the version of Postgres
       #   in use does not support materialized views.
@@ -205,26 +208,29 @@ def drop_materialized_view(name)
       #   Scenic.database.refresh_materialized_view(:search_results)
       # @example Concurrent refresh
       #   Scenic.database.refresh_materialized_view(:posts, concurrently: true)
+      # @example Cascade refresh
+      #   Scenic.database.refresh_materialized_view(:posts, cascade: true)
       #
       # @return [void]
       def refresh_materialized_view(name, concurrently: false, cascade: false)
         raise_unless_materialized_views_supported
 
+        if concurrently
+          raise_unless_concurrent_refresh_supported
+        end
+
         if cascade
           refresh_dependencies_for(name, concurrently: concurrently)
         end
 
-        if concurrently
-          raise_unless_concurrent_refresh_supported
+        if concurrently && populated?(name)
           execute "REFRESH MATERIALIZED VIEW CONCURRENTLY #{quote_table_name(name)};"
         else
           execute "REFRESH MATERIALIZED VIEW #{quote_table_name(name)};"
         end
       end
 
-      # True if supplied relation name is populated. Useful for checking the
-      # state of materialized views which may error if created `WITH NO DATA`
-      # and used before they are refreshed. True for all other relation types.
+      # True if supplied relation name is populated.
       #
       # @param name The name of the relation
       #
@@ -235,7 +241,7 @@ def refresh_materialized_view(name, concurrently: false, cascade: false)
       def populated?(name)
         raise_unless_materialized_views_supported
 
-        schemaless_name = name.split(".").last
+        schemaless_name = name.to_s.split(".").last
 
         sql = "SELECT relispopulated FROM pg_class WHERE relname = '#{schemaless_name}'"
         relations = execute(sql)

spec/scenic/adapters/postgres_spec.rb

@@ -149,6 +149,14 @@ module Adapters
               adapter.refresh_materialized_view(:tests, concurrently: true)
             }.to raise_error e
           end
+
+          it "falls back to non-concurrent refresh if not populated" do
+            adapter = Postgres.new
+            adapter.create_materialized_view(:testing, "SELECT unnest('{1, 2}'::int[])", no_data: true)
+
+            expect { adapter.refresh_materialized_view(:testing, concurrently: true) }
+              .not_to raise_error
+          end
         end
       end