prevent collectionId relation field change

forms/collection_upsert.go

@@ -245,7 +245,28 @@ func (form *CollectionUpsert) checkRelationFields(value any) error {
 
 		options, _ := field.Options.(*schema.RelationOptions)
 		if options == nil {
-			continue
+			return validation.Errors{fmt.Sprint(i): validation.Errors{
+				"options": validation.NewError(
+					"validation_schema_invalid_relation_field_options",
+					"The relation field has invalid field options.",
+				)},
+			}
+		}
+
+		// prevent collectionId change
+		oldField := form.collection.Schema.GetFieldById(field.Id)
+		if oldField != nil {
+			oldOptions, _ := oldField.Options.(*schema.RelationOptions)
+			if oldOptions != nil && oldOptions.CollectionId != options.CollectionId {
+				return validation.Errors{fmt.Sprint(i): validation.Errors{
+					"options": validation.Errors{
+						"collectionId": validation.NewError(
+							"validation_field_relation_change",
+							"The relation collection cannot be changed.",
+						),
+					}},
+				}
+			}
 		}
 
 		collection, err := form.dao.FindCollectionByNameOrId(options.CollectionId)

forms/collection_upsert_test.go

@@ -291,6 +291,26 @@ func TestCollectionUpsertValidateAndSubmit(t *testing.T) {
 			}`,
 			[]string{"type"},
 		},
+		{
+			"update failure - changing relation collection",
+			"users",
+			`{
+				"schema": [
+					{
+						"id": "lkeigvv3",
+						"name": "rel",
+						"type": "relation",
+						"options": {
+							"collectionId": "wzlqyes4orhoygb",
+							"cascadeDelete": false,
+							"maxSelect": 1,
+							"displayFields": null
+						}
+					}
+				]
+			}`,
+			[]string{"schema"},
+		},
 		{
 			"update failure - all fields",
 			"demo2",