Allow dynamic instance method calls on FactoryBot objects in Cypress

app/controllers/cypress/factories_controller.rb

@@ -5,28 +5,57 @@ module Cypress
   # It is inspired by this blog post by Tom Conroy:
   # https://tbconroy.com/2018/04/07/creating-data-with-factorybot-for-rails-cypress-tests/
   class FactoriesController < CypressController
-    # Wrapper around FactoryBot.create to create a factory via a POST request.
+    # Creates an instance of the factory (via FactoryBot) and returns it as JSON.
     def create
-      unless params["0"].is_a?(String)
-        msg = "First argument must be a string indicating the factory name."
-        msg += " But we got: '#{params["0"]}'"
-        raise(ArgumentError, msg)
-      end
+      factory_name = validate_factory_name(params["0"])
+      attributes, should_validate = params_to_attributes(
+        params.except(:controller, :action, :number)
+      )
+      res = create_class_instance_via_factorybot(attributes, should_validate)
+
+      # The factory name is included in the response such that it can be passed
+      # to call_instance_method later on in order to determine the class of the instance.
+      render json: res.as_json.merge({ factory_name: factory_name }), status: :created
+    end
 
-      attributes, should_validate = params_to_attributes(params.except(:controller, :action,
-                                                                       :number))
+    # Calls the instance method on the instance created by FactoryBot.create().
+    # Expects as arguments the factory name, the id of the instance,
+    # the method name and the method arguments to be passed to the instance method.
+    def call_instance_method
+      factory_name = validate_factory_name(params["factory_name"]).capitalize
+      id = params["instance_id"].to_i
+      method_name = params["method_name"]
+      method_args = params["method_args"]
+      method_args, _validate = params_to_attributes(method_args) if method_args.present?
 
-      res = if should_validate
-        FactoryBot.create(*attributes) # default case
-      else
-        FactoryBot.build(*attributes).tap { |instance| instance.save(validate: false) }
+      # Find the instance
+      begin
+        instance = factory_name.constantize.find(id)
+      rescue ActiveRecord::RecordNotFound
+        result = { error: "Instance where you'd like to call '#{method_name}' on was not found" }
+        return render json: result.to_json, status: :bad_request
       end
 
-      render json: res.to_json, status: :created
+      # Call the instance method & return the result
+      begin
+        result = instance.send(method_name, *method_args)
+        render json: result.to_json, status: :created
+      rescue NoMethodError => _e
+        result = { error: "Method '#{method_name}' not found on instance" }
+        render json: result.to_json, status: :bad_request
+      end
     end
 
     private
 
+      def validate_factory_name(factory_name)
+        return factory_name if factory_name.is_a?(String)
+
+        msg = "First argument must be a string indicating the factory name."
+        msg += " But we got: '#{factory_name}'"
+        raise(ArgumentError, msg)
+      end
+
       def params_to_attributes(params)
         should_validate = true
 
@@ -35,7 +64,7 @@ def params_to_attributes(params)
             if value.key?("validate")
               should_validate = (value["validate"] != "false")
             else
-              value.transform_keys(&:to_sym)
+              transform_hash(value)
             end
           elsif value.is_a?(String)
             value.to_sym
@@ -46,5 +75,34 @@ def params_to_attributes(params)
 
         return attributes, should_validate
       end
+
+      # Converts the keys of the hash to symbols. Furthermore, if the hash
+      # contains nested hashes with keys that are all integers, it converts
+      # the nested hashes to arrays of strings.
+      #
+      # The latter is important for calls like the following in Cypress:
+      # FactoryBot.create("tutorial",
+      #   { lecture_id: this.lecture.id, tutor_ids: [this.tutor1.id, this.tutor2.id] }
+      # )
+      # Without this transformation, the create() method in this controller
+      # would receive [:tutorial, {"lecture_id"=>"1", "tutor_ids"=>{"0"=>"42", "1"=>"43"}}],
+      # whereas what we need is: [:tutorial, {"lecture_id"=>"1", "tutor_ids"=>["42", "43"]}].
+      def transform_hash(value)
+        value.transform_keys(&:to_sym).transform_values do |v|
+          if v.is_a?(Hash) && v.keys.all? { |key| key.to_i.to_s }
+            v.values.map(&:to_s)
+          else
+            v
+          end
+        end
+      end
+
+      def create_class_instance_via_factorybot(attributes, should_validate)
+        if should_validate
+          FactoryBot.create(*attributes) # default case
+        else
+          FactoryBot.build(*attributes).tap { |instance| instance.save(validate: false) }
+        end
+      end
   end
 end

app/controllers/cypress/user_creator_controller.rb

@@ -1,6 +1,8 @@
 module Cypress
   # Creates a user for use in Cypress tests.
   class UserCreatorController < CypressController
+    CYPRESS_PASSWORD = "cypress123".freeze
+
     def create
       unless params[:role].is_a?(String)
         msg = "First argument must be a string indicating the user role."
@@ -10,13 +12,15 @@ def create
 
       role = params[:role]
       is_admin = (role == "admin")
+      random_hash = SecureRandom.hex(6)
 
-      user = User.create(name: "#{role} Cypress", email: "#{role}@mampf.cypress",
-                         password: "cypress123", consents: true, admin: is_admin,
+      user = User.create(name: "#{role} Cypress #{random_hash}",
+                         email: "#{role}-#{random_hash}@mampf.cypress",
+                         password: CYPRESS_PASSWORD, consents: true, admin: is_admin,
                          locale: I18n.default_locale)
       user.confirm
 
-      render json: user.to_json, status: :created
+      render json: user.as_json.merge({ password: CYPRESS_PASSWORD }), status: :created
     end
   end
 end

config/routes.rb

@@ -11,6 +11,7 @@
   if Rails.env.test?
     namespace :cypress do
       resources :factories, only: :create
+      post "factories/call_instance_method", to: "factories#call_instance_method"
       resources :database_cleaner, only: :create
       resources :user_creator, only: :create
       resources :i18n, only: :create

spec/cypress/e2e/meta/factory_bot_spec.cy.js

@@ -0,0 +1,47 @@
+import FactoryBot from "../../support/factorybot";
+
+describe("FactoryBot.create()", () => {
+  beforeEach(function () {
+    cy.createUserAndLogin("teacher").as("teacher");
+  });
+
+  it("allows to call create() with array as argument", function () {
+    cy.createUser("generic").as("tutor1");
+    cy.createUser("generic").as("tutor2");
+    FactoryBot.create("lecture", { teacher_id: this.teacher.id }).as("lecture");
+
+    cy.then(() => {
+      // here we pass in an array as argument to tutor_ids
+      FactoryBot.create("tutorial",
+        { lecture_id: this.lecture.id, tutor_ids: [this.tutor1.id, this.tutor2.id] },
+      );
+    });
+  });
+});
+
+describe("FactoryBot.create().call", () => {
+  beforeEach(function () {
+    cy.createUser("teacher").as("teacher");
+    cy.createUserAndLogin("generic");
+  });
+
+  it("allows to call instance methods after assigning them to an alias", function () {
+    FactoryBot.create("lecture", { teacher_id: this.teacher.id }).as("lecture");
+
+    cy.then(() => {
+      // via alias in global this namespace
+      this.lecture.call.long_title().then((res) => {
+        cy.log(res);
+      });
+    });
+  });
+
+  it("allows to call instance methods directly (without an alias)", function () {
+    FactoryBot.create("lecture", { teacher_id: this.teacher.id }).then((lecture) => {
+      // via return value of FactoryBot.create() directly (no alias intermediate)
+      lecture.call.long_title().then((res) => {
+        cy.log(res);
+      });
+    });
+  });
+});

spec/cypress/support/commands.js

@@ -105,8 +105,8 @@ Cypress.Commands.add("login", (user) => {
 });
 
 Cypress.Commands.add("createUserAndLogin", (role) => {
-  cy.createUser(role).then((user) => {
-    cy.login({ email: `${role}@mampf.cypress`, password: "cypress123" }).then((_) => {
+  return cy.createUser(role).then((user) => {
+    cy.login({ email: user.email, password: user.password }).then((_) => {
       cy.wrap(user);
     });
   });

spec/cypress/support/factorybot.js

@@ -9,19 +9,98 @@ class FactoryBot {
    * @param args The arguments to pass to FactoryBot.create(), e.g.
    * factory name, traits, and attributes. Pass them in as separated
    * string arguments. Attributes should be passed as an object.
-   * @returns The FactoryBot.create() response
-   *
-   * @example
+   * You are also able to call instance methods on the created record later.
+   * @returns The FactoryBot.create() response.
+   * @examples
    * FactoryBot.create("factory_name", "with_trait", { another_attribute: ".pdf"})
+   * FactoryBot.create("factory_name").then(res => {res.call.any_rails_method(42)})
+   * FactoryBot.create("tutorial",
+   *  { lecture_id: this.lecture.id, tutor_ids: [this.tutor1.id, this.tutor2.id] })
    */
   create(...args) {
-    return BackendCaller.callCypressRoute("factories", "FactoryBot.create()", args);
+    const response = BackendCaller.callCypressRoute("factories", "FactoryBot.create()", args);
+    return this.#createProxy(response);
   }
 
   createNoValidate(...args) {
     args.push({ validate: false });
     return this.create(...args);
   }
+
+  /**
+   * Wraps the given Cypress response such that arbitrary methods (dynamic methods)
+   * can be called on the resulting object.
+   */
+  #createProxy(obj) {
+    const outerContext = this;
+
+    return new Proxy(obj, {
+      get: function (target, property, receiver) {
+        if (property !== "as" && property !== "then") {
+          return Reflect.get(target, property, receiver);
+        }
+
+        // Trap the Cypress "as" and "then" methods to allow dynamic method calls
+        return function (...asOrThenArgs) {
+          if (property === "then") {
+            const callback = asOrThenArgs[0];
+            asOrThenArgs[0] = function (callbackObj) {
+              outerContext.#defineCallProperty(callbackObj);
+              return callback(callbackObj);
+            };
+            return target[property](...asOrThenArgs);
+          }
+
+          if (property === "as") {
+            return target.as(...asOrThenArgs).then((asResponse) => {
+              outerContext.#defineCallProperty(asResponse);
+            });
+          }
+
+          throw new Error(`Unknown property that should not be wrapped: ${property}`);
+        };
+      },
+    });
+  }
+
+  #defineCallProperty(response) {
+    const factoryName = response["factory_name"];
+    if (!factoryName) {
+      let msg = "FactoryBot call response does not contain factory_name key.";
+      msg += " Did you really use FactoryBot.create() (or similar) to create the record?";
+      throw new Error(msg);
+    }
+
+    if (typeof response.id !== "number") {
+      let msg = "FactoryBot call response does not contain a valid id key (number).";
+      msg += " Did you really use FactoryBot.create() (or similar) to create the record?";
+      throw new Error(msg);
+    }
+
+    const call = this.#allowDynamicMethods({}, factoryName, response.id);
+    response.call = call;
+  }
+
+  #allowDynamicMethods(obj, factoryName, instanceId) {
+    return new Proxy(obj, {
+      get: function (target, property, receiver) {
+        // If the property does not exist, define it as a new function
+        if (!(property in target)) {
+          target[property] = function () {
+            const payload = {
+              factory_name: factoryName,
+              instance_id: instanceId,
+              method_name: property,
+              method_args: Array.from(arguments),
+            };
+            return BackendCaller.callCypressRoute("factories/call_instance_method",
+              `FactoryBot.create().call.${property}()`, payload);
+          };
+        }
+        return Reflect.get(target, property, receiver);
+      },
+    });
+  }
 }
 
 export default new FactoryBot();