Add support for multi db setups with a different adapter

I was implementing solid_cable using SQLite as an adapter and came across this issue, where the schema dumper was trying to dump the functions and triggers for the SQLite solid cable schema. Obviously, this isn't possible.

I've modified the code to hook into the `ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaDumper` instead of the generic `ActiveRecord::SchemaDumper` and added a test

This should also fix teoljungberg#155

fx.gemspec

@@ -27,5 +27,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "activerecord", ">= 7.0"
   spec.add_dependency "railties", ">= 7.0"
 
+  spec.add_development_dependency "sqlite3"
+
   spec.required_ruby_version = ">= 3.0"
 end

lib/fx.rb

@@ -21,7 +21,7 @@ module Fx
   def self.load
     ActiveRecord::Migration::CommandRecorder.include(Fx::CommandRecorder)
     ActiveRecord::ConnectionAdapters::AbstractAdapter.include(Fx::Statements)
-    ActiveRecord::SchemaDumper.prepend(Fx::SchemaDumper)
+    ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaDumper.prepend(Fx::SchemaDumper)
 
     true
   end

spec/fx/schema_dumper_spec.rb

@@ -113,6 +113,40 @@
     expect(output).to include("EXECUTE FUNCTION uppercase_users_name()")
   end
 
+  context "with a sqlite adapter" do
+    let(:sqlite_connection) do
+      ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
+      ActiveRecord::Base.connection
+    end
+    after :each do
+      sqlite_connection.disconnect!
+    end
+
+    it "does not dump functions or triggers for SQLite connections" do
+      sql_definition = <<~EOS
+        CREATE OR REPLACE FUNCTION my_function()
+        RETURNS text AS $$
+        BEGIN
+            RETURN 'test';
+        END;
+        $$ LANGUAGE plpgsql;
+      EOS
+      connection.create_function :my_function, sql_definition: sql_definition
+      connection.create_table :my_table
+      postgres_stream = StringIO.new
+      sqlite_stream = StringIO.new
+
+      dump(connection: connection, stream: postgres_stream)
+      dump(connection: sqlite_connection, stream: sqlite_stream)
+
+      output = postgres_stream.string
+
+      expect(output).to include("create_function :my_function")
+      expect(output).to include("RETURN 'test';")
+      expect(output).to include('create_table "my_table"')
+    end
+  end
+
   def dump(connection:, stream:)
     if Rails.version >= "7.2"
       ActiveRecord::SchemaDumper.dump(connection.pool, stream)