fix: Avoid dumping unique_constraint when attisdropped

Fixes #347

Author: BuonOmo

lib/active_record/connection_adapters/cockroachdb/schema_statements.rb

@@ -222,6 +222,38 @@ def foreign_keys(table_name)
           end
         end
 
+        # OVERRIDE: Verify that the related attribute to the unique_constraint is not dropped.
+        #  See https://github.com/cockroachdb/activerecord-cockroachdb-adapter/issues/347.
+        def unique_constraints(table_name)
+          scope = quoted_scope(table_name)
+
+          unique_info = internal_exec_query(<<~SQL, "SCHEMA", allow_retry: true, materialize_transactions: false)
+            SELECT c.conname, c.conrelid, c.conkey, c.condeferrable, c.condeferred
+            FROM pg_constraint c
+            JOIN pg_class t ON c.conrelid = t.oid
+            JOIN pg_namespace n ON n.oid = c.connamespace
+            JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = c.conkey[1]    -- OVERRIDE
+            WHERE c.contype = 'u'
+              AND t.relname = #{scope[:name]}
+              AND n.nspname = #{scope[:schema]}
+              AND not a.attisdropped                                                     -- OVERRIDE
+          SQL
+
+          unique_info.map do |row|
+            conkey = row["conkey"].delete("{}").split(",").map(&:to_i)
+            columns = column_names_from_column_numbers(row["conrelid"], conkey)
+
+            deferrable = extract_constraint_deferrable(row["condeferrable"], row["condeferred"])
+
+            options = {
+              name: row["conname"],
+              deferrable: deferrable
+            }
+
+            UniqueConstraintDefinition.new(table_name, columns, options)
+          end
+        end
+
         # CockroachDB uses unique_rowid() for primary keys, not sequences. It's
         # possible to force a table to use sequences, but since it's not the
         # default behavior we'll always return nil for default_sequence_name.

test/cases/schema_dumper_test.rb

@@ -34,6 +34,27 @@ def test_schema_dumps_unique_constraints
       assert_match 't.unique_constraint ["position_3"], name: "test_unique_constraints_position_3"', output
     end
 
+    # See https://github.com/cockroachdb/activerecord-cockroachdb-adapter/issues/347
+    def test_dump_index_when_attisdropped_is_true
+      ActiveRecord::Base.with_connection do |conn|
+        conn.create_table :payments, force: true do |t|
+          t.text "name"
+          t.index "lower(name::STRING) ASC", name: "lower_name_index_on_payments", unique: true
+        end
+      end
+
+      stream = StringIO.new
+      ActiveRecord::Base.connection_pool.with_connection do |conn|
+        dumper = conn.create_schema_dumper({})
+        dumper.send(:table, "payments", stream)
+      end
+      stream.rewind
+      index_line = stream.each_line.find { _1[/lower_name_index_on_payments/] }
+      assert_match /t\.index/, index_line
+    ensure
+      ActiveRecord::Base.with_connection { _1.drop_table :payments, if_exists: true }
+    end
+
     def test_schema_dump_with_timestamptz_datetime_format
       migration, original, $stdout = nil, $stdout, StringIO.new