Do not truncate engines that cannot be truncated (#226)

Author: jer-k

README.md

@@ -158,10 +158,18 @@ Structure load from `db/clickhouse_structure.sql` file:
 
 For auto truncate tables before each test add to `spec/rails_helper.rb` file:
 
-```
+```ruby
 require 'clickhouse-activerecord/rspec'
 ```
-    
+
+### Minitest
+
+For auto truncate tables before each test add to `test/test_helper.rb` file:
+
+```ruby
+require 'clickhouse-activerecord/minitest'
+```
+
 ### Insert and select data
 
 ```ruby

lib/active_record/connection_adapters/clickhouse/schema_statements.rb

@@ -299,6 +299,38 @@ def settings_params(settings = {}, except: [])
                         .except(*except)
                         .to_param
         end
+
+        # Returns a hash of table names to their engine types
+        def table_engines(table_names = nil)
+          table_names_sql = if table_names.present?
+            "AND name IN (#{table_names.map { |name| "'#{name}'" }.join(', ')})"
+          end
+
+          sql = <<~SQL
+            SELECT name, engine FROM system.tables
+            WHERE database = currentDatabase()
+            #{table_names_sql}
+          SQL
+
+          result = do_system_execute(sql)
+          return {} if result.nil?
+
+          result['data'].to_h { |row| [row[0], row[1]] }
+        end
+
+        # @see https://clickhouse.com/docs/sql-reference/statements/truncate
+        # Additionally add 'Dictionary' because it is returned from 'show tables'.
+        TRUNCATE_UNSUPPORTED_ENGINES = %w[View File URL Buffer Null Dictionary].freeze
+
+        def build_truncate_statements(table_names)
+          engines = table_engines(table_names)
+          tables_to_truncate = table_names.select do |table_name|
+            engine = engines[table_name]
+            engine.nil? || !TRUNCATE_UNSUPPORTED_ENGINES.include?(engine)
+          end
+
+          super(tables_to_truncate)
+        end
       end
     end
   end

lib/clickhouse-activerecord/minitest.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module ClickhouseActiverecord
+  module TestHelper
+    def before_setup
+      super
+      ActiveRecord::Base.configurations.configurations.select { |x| x.env_name == Rails.env && x.adapter == 'clickhouse' }.each do |config|
+        ActiveRecord::Base.establish_connection(config)
+        ActiveRecord::Base.connection.truncate_tables(*ActiveRecord::Base.connection.tables)
+      end
+    end
+  end
+end
+
+ActiveSupport::TestCase.include(ClickhouseActiverecord::TestHelper) if defined?(ActiveSupport::TestCase)

lib/clickhouse-activerecord/rspec.rb

@@ -4,9 +4,7 @@
   config.before do
     ActiveRecord::Base.configurations.configurations.select { |x| x.env_name == Rails.env && x.adapter == 'clickhouse' }.each do |config|
       ActiveRecord::Base.establish_connection(config)
-      ActiveRecord::Base.connection.tables.each do |table|
-        ActiveRecord::Base.connection.execute("TRUNCATE TABLE #{table}")
-      end
+      ActiveRecord::Base.connection.truncate_tables(*ActiveRecord::Base.connection.tables)
     end
   end
 end

spec/active_record/connection_adapters/clickhouse/schema_statements_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+RSpec.describe 'ActiveRecord::ConnectionAdapters::Clickhouse::SchemaStatements' do
+  let(:connection) { ActiveRecord::Base.connection }
+
+  describe '#truncate_tables' do
+    before do
+      connection.execute('CREATE TABLE truncate_test (id UInt64, name String) ENGINE = MergeTree ORDER BY id')
+    end
+
+    after do
+      connection.execute('DROP DICTIONARY IF EXISTS truncate_test_dict')
+      connection.execute('DROP TABLE IF EXISTS truncate_test')
+      connection.execute('DROP TABLE IF EXISTS truncate_test2')
+      connection.execute('DROP VIEW IF EXISTS truncate_test_view')
+    end
+
+    it 'truncates multiple tables' do
+      connection.execute('CREATE TABLE truncate_test2 (id UInt64, value Int32) ENGINE = MergeTree ORDER BY id')
+      connection.exec_insert("INSERT INTO truncate_test (id, name) VALUES (1, 'Alice'), (2, 'Bob')")
+      connection.exec_insert("INSERT INTO truncate_test2 (id, value) VALUES (1, 100), (2, 200)")
+
+      expect(connection.select_value('SELECT count() FROM truncate_test')).to eq(2)
+      expect(connection.select_value('SELECT count() FROM truncate_test2')).to eq(2)
+
+      connection.truncate_tables('truncate_test', 'truncate_test2')
+
+      expect(connection.select_value('SELECT count() FROM truncate_test')).to eq(0)
+      expect(connection.select_value('SELECT count() FROM truncate_test2')).to eq(0)
+    end
+
+    it 'skips tables with unsupported engines' do
+      connection.execute('CREATE VIEW truncate_test_view AS SELECT * FROM truncate_test')
+      connection.execute(<<~SQL)
+        CREATE DICTIONARY truncate_test_dict (
+          id UInt64,
+          name String
+        )
+        PRIMARY KEY id
+        SOURCE(CLICKHOUSE(TABLE 'truncate_test'))
+        LIFETIME(MIN 0 MAX 0)
+        LAYOUT(FLAT())
+      SQL
+      connection.exec_insert("INSERT INTO truncate_test (id, name) VALUES (1, 'Alice')")
+
+      expect { connection.truncate_tables(*connection.tables) }.not_to raise_error
+
+      expect(connection.select_value('SELECT count() FROM truncate_test')).to eq(0)
+    end
+  end
+end