Add no_data option to materialized views

By default, creating a materialized view causes the associated query to
be run immediately. The `create view` statement does not complete until
the view is populated. While this is a good default, it may be
particularly expensive and potentially not desired during deploys.
Specifying `no_data: true`, allows the view to be created without a
refresh. It will not be usable until it is manually refreshed.

lib/generators/scenic/materializable.rb

@@ -10,13 +10,22 @@ module Materializable
           required: false,
           desc: "Makes the view materialized",
           default: false
+        class_option :no_data,
+          type: :boolean,
+          required: false,
+          desc: "Adds WITH NO DATA when materialized view creates/updates",
+          default: false
       end
 
       private
 
       def materialized?
         options[:materialized]
       end
+
+      def no_data?
+        options[:no_data]
+      end
     end
   end
 end

lib/generators/scenic/view/USAGE

@@ -6,6 +6,7 @@ Description:
   and a migration to replace the old version with the new.
 
   To create a materialized view, pass the '--materialized' option.
+  To create a materialized view with NO DATA, pass '--no-data' option.
 
 Examples:
     rails generate scenic:view searches

lib/generators/scenic/view/templates/db/migrate/create_view.erb

@@ -1,5 +1,5 @@
 class <%= migration_class_name %> < <%= activerecord_migration_class %>
   def change
-    create_view <%= formatted_plural_name %><%= ", materialized: true" if materialized? %>
+    create_view <%= formatted_plural_name %><%= create_view_options %>
   end
 end

lib/generators/scenic/view/templates/db/migrate/update_view.erb

@@ -4,7 +4,7 @@ class <%= migration_class_name %> < <%= activerecord_migration_class %>
     update_view <%= formatted_plural_name %>,
       version: <%= version %>,
       revert_to_version: <%= previous_version %>,
-      materialized: true
+      materialized: <%= no_data? ? "{ no_data: true }" : true %>
   <%- else -%>
     update_view <%= formatted_plural_name %>, version: <%= version %>, revert_to_version: <%= previous_version %>
   <%- end -%>

lib/generators/scenic/view/view_generator.rb

@@ -109,6 +109,11 @@ def formatted_plural_name
         end
       end
 
+      def create_view_options
+        return "" unless materialized?
+        ", materialized: #{no_data? ? '{ no_data: true }' : true}"
+      end
+
       def destroying_initial_view?
         destroying? && version == 1
       end

lib/scenic/adapters/postgres.rb

@@ -122,16 +122,23 @@ def drop_view(name)
       #
       # @param name The name of the materialized view to create
       # @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.
       #
       # This is typically called in a migration via {Statements#create_view}.
       #
       # @raise [MaterializedViewsNotSupportedError] if the version of Postgres
       #   in use does not support materialized views.
       #
       # @return [void]
-      def create_materialized_view(name, sql_definition)
+      def create_materialized_view(name, sql_definition, no_data: false)
         raise_unless_materialized_views_supported
-        execute "CREATE MATERIALIZED VIEW #{quote_table_name(name)} AS #{sql_definition};"
+        execute <<-SQL
+  CREATE MATERIALIZED VIEW #{quote_table_name(name)} AS
+  #{sql_definition}
+  #{'WITH NO DATA' if no_data};
+        SQL
       end
 
       # Updates a materialized view in the database.
@@ -144,17 +151,20 @@ def create_materialized_view(name, sql_definition)
       #
       # @param name The name of the view to update
       # @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.
       #
       # @raise [MaterializedViewsNotSupportedError] if the version of Postgres
       #   in use does not support materialized views.
       #
       # @return [void]
-      def update_materialized_view(name, sql_definition)
+      def update_materialized_view(name, sql_definition, no_data: false)
         raise_unless_materialized_views_supported
 
         IndexReapplication.new(connection: connection).on(name) do
           drop_materialized_view(name)
-          create_materialized_view(name, sql_definition)
+          create_materialized_view(name, sql_definition, no_data: no_data)
         end
       end
 

lib/scenic/statements.rb

@@ -9,8 +9,9 @@ module Statements
     # @param sql_definition [String] The SQL query for the view schema. An error
     #   will be raised if `sql_definition` and `version` are both set,
     #   as they are mutually exclusive.
-    # @param materialized [Boolean] Set to true to create a materialized view.
-    #   Defaults to false.
+    # @param materialized [Boolean, Hash] Set to true to create a materialized
+    #   view. Set to { no_data: true } to create materialized view without
+    #   loading data. Defaults to false.
     # @return The database response from executing the create statement.
     #
     # @example Create from `db/views/searches_v02.sql`
@@ -36,7 +37,11 @@ def create_view(name, version: nil, sql_definition: nil, materialized: false)
       sql_definition ||= definition(name, version)
 
       if materialized
-        Scenic.database.create_materialized_view(name, sql_definition)
+        Scenic.database.create_materialized_view(
+          name,
+          sql_definition,
+          no_data: no_data(materialized),
+        )
       else
         Scenic.database.create_view(name, sql_definition)
       end
@@ -75,8 +80,9 @@ def drop_view(name, revert_to_version: nil, materialized: false)
     #   as they are mutually exclusive.
     # @param revert_to_version [Fixnum] The version number to rollback to on
     #   `rake db rollback`
-    # @param materialized [Boolean] True if updating a materialized view.
-    #   Defaults to false.
+    # @param materialized [Boolean, Hash] True if updating a materialized view.
+    #   Set to { no_data: true } to update materialized view without loading
+    #   data. Defaults to false.
     # @return The database response from executing the create statement.
     #
     # @example
@@ -100,7 +106,11 @@ def update_view(name, version: nil, sql_definition: nil, revert_to_version: nil,
       sql_definition ||= definition(name, version)
 
       if materialized
-        Scenic.database.update_materialized_view(name, sql_definition)
+        Scenic.database.update_materialized_view(
+          name,
+          sql_definition,
+          no_data: no_data(materialized),
+        )
       else
         Scenic.database.update_view(name, sql_definition)
       end
@@ -141,5 +151,10 @@ def replace_view(name, version: nil, revert_to_version: nil, materialized: false
     def definition(name, version)
       Scenic::Definition.new(name, version).to_sql
     end
+
+    def no_data(materialized)
+      return false unless materialized.is_a? Hash
+      materialized.fetch(:no_data, false)
+    end
   end
 end

lib/scenic/view.rb

@@ -48,7 +48,6 @@ def to_schema
   create_view #{name.inspect}, #{materialized_option} sql_definition: <<-\SQL
     #{definition.indent(2)}
   SQL
-
       DEFINITION
     end
   end

spec/scenic/statements_spec.rb

@@ -52,12 +52,29 @@ module Scenic
 
     describe "create_view :materialized" do
       it "sends the create_materialized_view message" do
-        allow(Definition).to receive(:new)
-          .and_return(instance_double("Scenic::Definition").as_null_object)
+        definition = instance_double("Scenic::Definition", to_sql: "definition")
+        allow(Definition).to receive(:new).and_return(definition)
 
         connection.create_view(:views, version: 1, materialized: true)
 
-        expect(Scenic.database).to have_received(:create_materialized_view)
+        expect(Scenic.database).to have_received(:create_materialized_view).
+          with(:views, definition.to_sql, no_data: false)
+      end
+    end
+
+    describe "create_view :materialized with :no_data" do
+      it "sends the create_materialized_view message" do
+        definition = instance_double("Scenic::Definition", to_sql: "definition")
+        allow(Definition).to receive(:new).and_return(definition)
+
+        connection.create_view(
+          :views,
+          version: 1,
+          materialized: { no_data: true },
+        )
+
+        expect(Scenic.database).to have_received(:create_materialized_view).
+          with(:views, definition.to_sql, no_data: true)
       end
     end
 
@@ -108,7 +125,23 @@ module Scenic
         connection.update_view(:name, version: 3, materialized: true)
 
         expect(Scenic.database).to have_received(:update_materialized_view).
-          with(:name, definition.to_sql)
+          with(:name, definition.to_sql, no_data: false)
+      end
+
+      it "updates the materialized view in the database with NO DATA" do
+        definition = instance_double("Definition", to_sql: "definition")
+        allow(Definition).to receive(:new).
+          with(:name, 3).
+          and_return(definition)
+
+        connection.update_view(
+          :name,
+          version: 3,
+          materialized: { no_data: true },
+        )
+
+        expect(Scenic.database).to have_received(:update_materialized_view).
+          with(:name, definition.to_sql, no_data: true)
       end
 
       it "raises an error if not supplied a version or sql_defintion" do