Add support for force CREATE FUNCTION (#146)

* Switch from `CREATE FUNCTION` to `CREATE OR REPLACE FUNCTION`

In a rails app, with existing Clickhouse schema w/a function defined, a `rails db:schema:load` will not always succeed; this is because the function may already exist.

```
Code: 609. DB::Exception: User-defined function 'uuid7ToDateTime' already exists. (FUNCTION_ALREADY_EXISTS) (version 23.9.6.20 (official build))
```

lib/active_record/connection_adapters/clickhouse_adapter.rb

@@ -356,8 +356,8 @@ def create_table(table_name, **options, &block)
         end
       end
 
-      def create_function(name, body)
-        fd = "CREATE FUNCTION #{apply_cluster(quote_table_name(name))} AS #{body}"
+      def create_function(name, body, **options)
+        fd = "CREATE#{' OR REPLACE' if options[:force]} FUNCTION #{apply_cluster(quote_table_name(name))} AS #{body}"
         do_execute(fd, format: nil)
       end
 

lib/clickhouse-activerecord/schema_dumper.rb

@@ -112,7 +112,7 @@ def function(function, stream)
       stream.puts "  # FUNCTION: #{function}"
       sql = @connection.show_create_function(function)
       stream.puts "  # SQL: #{sql}" if sql
-      stream.puts "  create_function \"#{function}\", \"#{sql.gsub(/^CREATE FUNCTION (.*?) AS/, '').strip}\"" if sql
+      stream.puts "  create_function \"#{function}\", \"#{sql.gsub(/^CREATE FUNCTION (.*?) AS/, '').strip}\", force: true" if sql
     end
 
     def format_options(options)

spec/cluster/migration_spec.rb

@@ -70,9 +70,12 @@
           let(:directory) { 'dsl_create_function' }
 
           it 'creates a function' do
+            ActiveRecord::Base.connection.do_execute('CREATE FUNCTION forced_fun AS (x, k, b) -> k*x + b', format: nil)
+
             subject
 
-            expect(ActiveRecord::Base.connection.functions).to match_array(['some_fun'])
+            expect(ActiveRecord::Base.connection.functions).to match_array(['some_fun', 'forced_fun'])
+            expect(ActiveRecord::Base.connection.show_create_function('forced_fun').chomp).to eq('CREATE FUNCTION forced_fun AS (x, y) -> (x + y)')
           end
         end
       end

spec/fixtures/migrations/dsl_create_function/1_create_some_function.rb

@@ -3,5 +3,6 @@
 class CreateSomeFunction < ActiveRecord::Migration[7.1]
   def up
     create_function :some_fun, "(x,y) -> x + y"
+    create_function :forced_fun, "(x,y) -> x + y", force: true
   end
 end

spec/single/migration_spec.rb

@@ -369,9 +369,12 @@
       context 'dsl' do
         let(:directory) { 'dsl_create_function' }
         it 'creates a function' do
+          ActiveRecord::Base.connection.do_execute('CREATE FUNCTION forced_fun AS (x, k, b) -> k*x + b', format: nil)
+
           subject
 
-          expect(ActiveRecord::Base.connection.functions).to match_array(['some_fun'])
+          expect(ActiveRecord::Base.connection.functions).to match_array(['some_fun', 'forced_fun'])
+          expect(ActiveRecord::Base.connection.show_create_function('forced_fun').chomp).to eq('CREATE FUNCTION forced_fun AS (x, y) -> (x + y)')
         end
       end
     end