Adjust table creation to work with materialized views on schema loading

Author: csalvato

lib/active_record/connection_adapters/clickhouse/schema_creation.rb

@@ -82,6 +82,19 @@ def assign_database_to_subquery!(subquery)
             "#{current_database}.#{match[:table_name].sub('.', '')}"
         end
 
+        def add_materialized_to_clause!(create_sql, options)
+          if !options.to
+            create_sql << " ENGINE = Memory()"
+          else
+            target_table = options.to.split('.').last
+            table_structure = @conn.execute("DESCRIBE TABLE #{target_table}")['data']
+            column_definitions = table_structure.map do |field|
+              "`#{field[0]}` #{field[1]}"
+            end
+            create_sql << "TO #{options.to} (#{column_definitions.join(', ')}) "
+          end
+        end
+
         def add_to_clause!(create_sql, options)
           # If you do not specify a database explicitly, ClickHouse will use the "default" database.
           return unless options.to
@@ -97,23 +110,34 @@ def visit_TableDefinition(o)
           create_sql = +"CREATE#{table_modifier_in_create(o)} #{o.view ? "VIEW" : "TABLE"} "
           create_sql << "IF NOT EXISTS " if o.if_not_exists
           create_sql << "#{quote_table_name(o.name)} "
-          add_as_clause!(create_sql, o) if o.as && !o.view
-          add_to_clause!(create_sql, o) if o.materialized
 
-          statements = o.columns.map { |c| accept c }
-          statements << accept(o.primary_keys) if o.primary_keys
+          # Add column definitions for regular tables only
+          if !o.view && o.columns.present?
+            statements = o.columns.map { |c| accept c }
+            statements << accept(o.primary_keys) if o.primary_keys
 
-          if supports_indexes_in_create?
-            indexes = o.indexes.map do |expression, options|
-              accept(@conn.add_index_options(o.name, expression, **options))
+            if supports_indexes_in_create?
+              indexes = o.indexes.map do |expression, options|
+                accept(@conn.add_index_options(o.name, expression, **options))
+              end
+              statements.concat(indexes)
             end
-            statements.concat(indexes)
+
+            create_sql << "(#{statements.join(', ')})"
           end
 
-          create_sql << "(#{statements.join(', ')})" if statements.present?
-          # Attach options for only table or materialized view without TO section
-          add_table_options!(create_sql, o) if !o.view || o.view && o.materialized && !o.to
-          add_as_clause!(create_sql, o) if o.as && o.view
+          # Add TO clause for materialized views before AS clause
+          add_materialized_to_clause!(create_sql, o) if o.materialized && o.view
+
+          # Add AS clause for all views
+          add_as_clause!(create_sql, o) if o.as
+
+          # Add TO clause for regular views (non-materialized) after AS clause
+          add_to_clause!(create_sql, o) if o.to && !o.materialized
+
+          # Add table options for regular tables
+          add_table_options!(create_sql, o) if !o.view
+
           create_sql
         end
 

spec/single/materialized_view_spec.rb

@@ -0,0 +1,44 @@
+require 'spec_helper'
+
+RSpec.describe 'Materialized Views' do
+  before do
+    ActiveRecord::Schema.define do
+      create_table "events", id: false, options: "Log", force: :cascade do |t|
+        t.integer "quantity", default: -> { "CAST(1, 'Int8')" }, null: false
+        t.string "name", null: false
+        t.date "created_at", null: false
+      end
+    end
+  end
+
+  after do
+    ActiveRecord::Schema.define do
+      drop_table :events if table_exists?(:events)
+      drop_table :aggregated_events_mv if table_exists?(:aggregated_events_mv)
+      drop_table :aggregated_events if table_exists?(:aggregated_events)
+    end
+  end
+
+  it 'creates a materialized view with TO clause and column definitions' do
+    database = ActiveRecord::Base.connection_db_config.database
+
+    ActiveRecord::Schema.define do
+      create_table "aggregated_events", id: false, options: "SummingMergeTree ORDER BY (name, date) SETTINGS index_granularity = 8192", force: :cascade do |t|
+        t.string "name", null: false
+        t.date "date", null: false
+        t.integer "total_quantity", limit: 8, null: false
+        t.integer "event_count", limit: 8, null: false
+      end
+
+      create_table "aggregated_events_mv", view: true, materialized: true, to: "#{database}.aggregated_events", id: false, as: "SELECT name, created_at AS date, sum(quantity) AS total_quantity, count() AS event_count FROM #{database}.events GROUP BY name, created_at", force: :cascade do |t|
+      end
+    end
+
+    # Verify the view was created correctly
+    result = ActiveRecord::Base.connection.do_system_execute(
+      "SHOW CREATE TABLE #{database}.aggregated_events_mv"
+    )['data'].first.first
+
+    expect(result.squish).to eq('CREATE MATERIALIZED VIEW default.aggregated_events_mv TO default.aggregated_events ( `name` String, `date` Date, `total_quantity` UInt64, `event_count` UInt64 ) AS SELECT name, created_at AS date, sum(quantity) AS total_quantity, count() AS event_count FROM default.events GROUP BY name, created_at')
+  end
+end