Add constraint and separate out null column

db/migrate/20210608103235_add_issue_index_to_test_report.rb

@@ -5,7 +5,7 @@ class AddIssueIndexToTestReport < ActiveRecord::Migration[6.1]
 
   disable_ddl_transaction!
 
-  INDEX_NAME = 'index_test_reports_on_issue_id'
+  INDEX_NAME = 'index_requirements_management_test_reports_on_issue_id'
 
   def up
     add_concurrent_index :requirements_management_test_reports, :issue_id, name: INDEX_NAME

db/migrate/20210608110752_change_column_null_test_report_requirement.rb

@@ -3,23 +3,15 @@
 class ChangeColumnNullTestReportRequirement < ActiveRecord::Migration[6.1]
   include Gitlab::Database::MigrationHelpers
 
-  disable_ddl_transaction!
+  TARGET_TABLE = :requirements_management_test_reports
 
   def up
     with_lock_retries do
-      change_column_null :requirements_management_test_reports, :requirement_id, true
+      change_column_null TARGET_TABLE, :requirement_id, true
     end
-
-    add_concurrent_foreign_key :requirements_management_test_reports, :issues, column: :issue_id
   end
 
   def down
-    with_lock_retries do
-      remove_foreign_key_if_exists(:requirements_management_test_reports, column: :issue_id)
-    end
-
-    with_lock_retries do
-      change_column_null :requirements_management_test_reports, :requirement_id, false
-    end
+    # no-op as it's difficult to revert
   end
 end

db/migrate/20210608110760_add_requirement_test_reports_foreign_key.rb

+# frozen_string_literal: true
+
+class AddRequirementTestReportsForeignKey < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  TARGET_TABLE = :requirements_management_test_reports
+  CONSTRAINT_NAME = 'requirements_test_reports_requirement_id_xor_issue_id'
+
+  def up
+    add_concurrent_foreign_key TARGET_TABLE, :issues, column: :issue_id
+
+    add_check_constraint(TARGET_TABLE, 'num_nonnulls(requirement_id, issue_id) = 1', CONSTRAINT_NAME)
+  end
+
+  def down
+    remove_check_constraint TARGET_TABLE, CONSTRAINT_NAME
+
+    with_lock_retries do
+      remove_foreign_key_if_exists(TARGET_TABLE, column: :issue_id)
+    end
+  end
+end

db/schema_migrations/20210608110760

+b84505713afce3bf0673329a3a4eaf85a00d4f8948f56d43d365d6cc47ef629c
\ No newline at end of file

db/structure.sql

@@ -17464,7 +17464,8 @@ CREATE TABLE requirements_management_test_reports (
     author_id bigint,
     state smallint NOT NULL,
     build_id bigint,
-    issue_id bigint
+    issue_id bigint,
+    CONSTRAINT requirements_test_reports_requirement_id_xor_issue_id CHECK ((num_nonnulls(requirement_id, issue_id) = 1))
 );
 
 CREATE SEQUENCE requirements_management_test_reports_id_seq
@@ -24426,6 +24427,8 @@ CREATE INDEX index_requirements_management_test_reports_on_author_id ON requirem
 
 CREATE INDEX index_requirements_management_test_reports_on_build_id ON requirements_management_test_reports USING btree (build_id);
 
+CREATE INDEX index_requirements_management_test_reports_on_issue_id ON requirements_management_test_reports USING btree (issue_id);
+
 CREATE INDEX index_requirements_management_test_reports_on_requirement_id ON requirements_management_test_reports USING btree (requirement_id);
 
 CREATE INDEX index_requirements_on_author_id ON requirements USING btree (author_id);
@@ -24718,8 +24721,6 @@ CREATE UNIQUE INDEX index_terraform_states_on_uuid ON terraform_states USING btr
 
 CREATE UNIQUE INDEX index_test_case_failures_unique_columns ON ci_test_case_failures USING btree (test_case_id, failed_at DESC, build_id);
 
-CREATE INDEX index_test_reports_on_issue_id ON requirements_management_test_reports USING btree (issue_id);
-
 CREATE INDEX index_timelogs_on_issue_id ON timelogs USING btree (issue_id);
 
 CREATE INDEX index_timelogs_on_merge_request_id ON timelogs USING btree (merge_request_id);

ee/app/models/requirements_management/test_report.rb

@@ -12,6 +12,7 @@ module RequirementsManagement
 
     validates :state, presence: true
     validate :only_one_requirement_association
+    validate :only_requirement_type_issue
 
     enum state: { passed: 1, failed: 2 }
 
@@ -69,7 +70,10 @@ module RequirementsManagement
     end
 
     def only_one_requirement_association
-      errors.add(:base, 'Must be associated with either a RequirementsManagement::Requirement and an Issue of type `requirement`, but not both') unless !!requirement ^ !!requirement_issue
+      errors.add(:base, 'Must be associated with either a RequirementsManagement::Requirement OR an Issue of type `requirement`, but not both') unless !!requirement ^ !!requirement_issue
+    end
+
+    def only_requirement_type_issue
       errors.add(:requirement_issue, 'must be an issue of type `Requirement`') if requirement_issue && !requirement_issue.requirement?
     end
   end

ee/spec/models/requirements_management/test_report_spec.rb

@@ -17,7 +17,7 @@ RSpec.describe RequirementsManagement::TestReport do
 
     let(:requirement) { build(:requirement) }
     let(:requirement_issue) { build(:requirement_issue) }
-    let(:requirement_error) { /Must be associated with either a RequirementsManagement::Requirement and an Issue of type `requirement`, but not both/ }
+    let(:requirement_error) { /Must be associated with either a RequirementsManagement::Requirement OR an Issue of type `requirement`, but not both/ }
 
     it { is_expected.to validate_presence_of(:state) }