Domain is made up of several things.

• Entities <<<<<<< HEAD
  • Enterprise-wide business rules
  • Made up of classes that can contain methods
  • Business objects of the application
  • Used application-wide
  • Least likely to change when something in the application changes
• Usecases
  • Application-specific business rules
  • Encapsulate all the usecases of the application
  • Orchestrate the flow of data throughout the app
  • Should not be affected by any UI changes whatsoever
  • Might change if the functionality and flow of application change
• Repositories
  • Abstract classes that define the expected functionality of outer layers
  • Are not aware of outer layers, simply define expected functionality
    • E.g. The Login usecase expects a Repository that has login functionality
  • Passed to Usecases from outer layers =======
  • Enterprise-wide business rules
  • Made up of classes that can contain methods
  • Business objects of the application
  • Used application-wide
  • Least likely to change when something in the application changes
• Usecases
  • Application-specific business rules
  • Encapsulate all the usecases of the application
  • Orchestrate the flow of data throughout the app
  • Should not be affected by any UI changes whatsoever
  • Might change if the functionality and flow of application change
• Repositories
  • Abstract classes that define the expected functionality of outer layers
  • Are not aware of outer layers, simply define expected functionality
    • E.g. The Login usecase expects a Repository that has login functionality
  • Passed to Usecases from outer layers

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Domain represents the inner-most layer. Therefore, it the most abstract layer in the architecture.

App

App is the layer outside Domain. App crosses the boundaries of the layers to communicate with Domain. However, the Dependency Rule is never violated. Using polymorphism, App communicates with Domain using inherited class: classes that implement or extend the Repositories present in the Domain layer. Since polymorphism is used, the Repositories passed to Domain still adhere to the Dependency Rule since as far as Domain is concerned, they are abstract. The implementation is hidden behind the polymorphism.

Contents of App

Since App is the presentation layer of the application, it is the most framework-dependent layer, as it contains the UI and the event handlers of the UI. For every page in the application, App defines at least 3 classes: a Action, a Reducers, and a View.

• ACTIONS <<<<<<< HEAD

  • In a nutshell, actions are events. Actions send data from the application (user interactions, internal events such as API calls, and form submissions) to the store. The store gets information only from actions. Internal actions are simple JavaScript objects that have a type property (usually constant), describing the type of action and payload of information being sent to the store.

    {
        type: LOGIN_FORM_SUBMIT,
        payload: {username: ‘alex’, password: ‘123456’}
    }
    

    Actions are created with action creators. That sounds obvious, I know. They are just functions that return actions.

    function authUser(form) {
        return {
            type: LOGIN_FORM_SUBMIT,
            payload: form
        }
    }
    

    Calling actions anywhere in the app, then, is very easy. Use the dispatch method, like so:

    dispatch(authUser(form));
    

• REDUCERS

  • We’ve already discussed what a reducer is in functional JavaScript. It’s based on the array reduce method, where it accepts a callback (reducer) and lets you get a single value out of multiple values, sums of integers, or an accumulation of streams of values. In Redux, reducers are functions (pure) that take the current state of the application and an action and then return a new state. Understanding how reducers work is important because they perform most of the work. Here is a very simple reducer that takes the current state and an action as arguments and then returns the next state:

    function handleAuth(state, action) {
        return _.assign({}, state, {
            auth: action.payload
        });
    }
    

    For more complex apps, using the combineReducers() utility provided by Redux is possible (indeed, recommended). It combines all of the reducers in the app into a single index reducer. Every reducer is responsible for its own part of the app’s state, and the state parameter is different for every reducer. The combineReducers() utility makes the file structure much easier to maintain.

    If an object (state) changes only some values, Redux creates a new object, the values that didn’t change will refer to the old object and only new values will be created. That’s great for performance. To make it even more efficient you can add Immutable.js.

    const rootReducer = combineReducers({
        handleAuth: handleAuth,
        editProfile: editProfile,
        changePassword: changePassword
    });
    

• Extra

  • Utility classes (any commonly used functions like timestamp getters etc..)
  • Constants classes (const strings for convenience)
  • Navigator (if needed)

Data

Represents the data-layer of the application. The Data module, which is a part of the outermost layer, is responsible for data retrieval. This can be in the form of API calls to a server, a local database, or even both.

Contents of Data

• Repositories
  • Every Repository should implement Repository from the Domain layer.
  • Using polymorphism, these repositories from the data layer can be passed across the boundaries of layers, starting from the View down to the Usecases through the Controller and Presenter.
  • Retrieve data from databases or other methods.
  • Responsible for any API calls and high-level data manipulation such as
    • Registering a user with a database
    • Uploading data
    • Downloading data
    • Handling local storage
    • Calling an API
• Models (not a must depending on the application)
  • Extensions of Entities with the addition of extra members that might be platform-dependent. For example, in the case of local databases, this can be manifested as an isDeleted or an isDirty entry in the local database. Such entries cannot be present in the Entities as that would violate the Dependency Rule since Domain should not be aware of the implementation.
  • In the case of our application, models in the Data layer will not be necessary as we do not have a local database. Therefore, it is unlikely that we will need extra entries in the Entities that are platform-dependent.
• Mappers
  • Map Entity objects to Models and vice-versa.
  • Static classes with static methods that receive either an Entity or a Model and return the other.
  • Only necessary in the presence of Models
• Extra
  • Utility classes if needed
  • Constants classes if needed

Device

Part of the outermost layer, Device communicates directly with the platform i.e. Android and iOS. Device is responsible for Native functionality such as GPS and other functionality present within the platform itself like the filesystem. Device calls all Native APIs.

Contents of Data

• Devices

  • Similar to Repositories in Data, Devices are classes that communicate with a specific functionality in the platform.
  • Passed through the layers the same way Repositories are pass across the boundaries of the layer: using polymorphism between the App and Domain layer. That means the Controller passes it to the Presenter then the Presenter passes it polymorphically to the Usecase, which receives it as an abstract class.

• Extra

  • Utility classes if needed

  • Constants classes if needed =======

  • In a nutshell, actions are events. Actions send data from the application (user interactions, internal events such as API calls, and form submissions) to the store. The store gets information only from actions. Internal actions are simple JavaScript objects that have a type property (usually constant), describing the type of action and payload of information being sent to the store.

    {
        type: LOGIN_FORM_SUBMIT,
        payload: {username: ‘alex’, password: ‘123456’}
    }
    

    Actions are created with action creators. That sounds obvious, I know. They are just functions that return actions.

    function authUser(form) {
        return {
            type: LOGIN_FORM_SUBMIT,
            payload: form
        }
    }
    

    Calling actions anywhere in the app, then, is very easy. Use the dispatch method, like so:

    dispatch(authUser(form));
    

• REDUCERS

  • We’ve already discussed what a reducer is in functional JavaScript. It’s based on the array reduce method, where it accepts a callback (reducer) and lets you get a single value out of multiple values, sums of integers, or an accumulation of streams of values. In Redux, reducers are functions (pure) that take the current state of the application and an action and then return a new state. Understanding how reducers work is important because they perform most of the work. Here is a very simple reducer that takes the current state and an action as arguments and then returns the next state:

    function handleAut