MobX State Tree (MST) is a library that helps you organize your application states in a very structured manner. It allows you to create a component model, but for your data!

Course instructor Michel Weststrate—creator of Mobx—will teach you to model application state after your problem domain with MST. You will get hands-on practice and see how MST lets you solve problems with its out-of-the-box support for asynchronous actions, patches, snapshots, and middleware.

Over the 17 lessons, you’ll build a little bookshop application using React, MST, and create-react-app, while learning how to manage the lifecycle of your data by describing data models. 

Join Michel in one of the most popular courses on egghead!

In this lesson, we introduce the running example of this course, a wishlist app. We will take a look at the core of mobx-state-tree (MST), models. Models describe the shape of your state and perform type validation. 

You will learn:
* Defining models using types.Model
* Instantiating models from JSON using Model.create
* Primitive types: types.string & types.number
* Type inference for primitive types
* types.array
* types.optional
* Composing models into a model tree
* Testing models using jest

Describe Your Application Domain Using mobx-state-tree(MST) Models

Models are not just a nifty feature for type checking. They enable you to attach behavior to your actions in a straightforward and highly discoverable way

In this lesson, you will learn:
* How to define actions on models
* How to avoid `this` issues by using self
* Models can only be modified using actions, and are further read-only from the outside

To learn more about TypeScript check out John Lindquist's wonderful course, [Up and Running with TypeScript](https://egghead.io/courses/up-and-running-with-typescript).


Attach Behavior to mobx-state-tree Models Using Actions

Testing models is straightforward. Especially because MST provides powerful tools to track exactly how your state changes over time. Track snapshots, action invocations or even patches to verify the correctness of your actions!

In this lesson you will learn:
* To obtain immutable snapshots of the state using `getSnapshot`
* To record snapshots using `onSnapshot`
* To store and test modifications over time using `onPatch`
* Using Jest's snapshot test feature to verify snapshots and patches
* That MST can infer the type of a snapshot for you

Test mobx-state-tree Models by Recording Snapshots or Patches

Redundant data or caching data is a constant source of bugs. MST adheres to the philosophy that no data that can be derived should ever get stored. In this lesson, you will learn how to introduce views that declaratively derive data and which cache data smartly.

In this lesson you will learn:
* How to introduce views on models
* That computed properties are powered by Mobx computed fields
* How to combine MST with Mobx utilities like `reaction`

To learn more about MobX basics check out my course, [Manage Complex State in React Apps with MobX](https://egghead.io/courses/manage-complex-state-in-react-apps-with-mobx)

Derive Information from Models Using Views

mobx-state-tree uses Mobx behind the scenes, making it super straightforward to render MST models in React. By using the `observer` wrapper, React components will automatically react to any relevant updates of the rendered models in the future.

In this lesson you will learn:
* How `observer` from the 'mobx-react' package is enough to render data in React components, and get notified of updates
* That using models in components keeps components dumb so that components can often be stateless function components
* The mobx devtools can be used to visualize that mobx-react finds the minimal sets of components to re-render after each change automatically for you

Render mobx-state-tree Models in React

We will expand our UI, and give the user the possibility to edit his wishlist. We will use the earlier defined actions. We also will use model clones only to modify data temporarily, and after approving the changes, apply them back to the original model. 

In this lesson you will learn: 
* How to call model actions from a component
* Using `clone` to create a full, deep clone of any model instance
* Using `applySnapshot` to update the state of a model instance given a snapshot.

Build Forms with React to Edit mobx-state-tree Models

In this lesson we will dive a bit more into the tree semantics of MST. 

In this lesson you will learn:
* Actions can only modify their own subtree
* The use of `getParent` to find the parent of a model instance
* Using `destroy` to remove an instance entirely from the tree


Remove Model Instances from the Tree

It is time to add new entries to the wishlist. We will achieve this by reusing forms and models we've built so far.

In this lesson you will learn:
* MST is not limited to a single state tree. Every model can form a tree on its own
* Appending model instances to the state tree

Create an Entry Form to Add Models to the State Tree

For an optimal user and developer experience, storing state in local storage is often a must.

In this lesson you will learn:
* Using `onSnapshot` to get notified about new snapshots
* Storing snapshots in local storage
* Restore a state tree from local storage
* Verifying whether a snapshot conforms to a model using `Model.is(...)`

Store Store in Local Storage

In this lesson, we will set up Hot Module Reloading(HMR), making it possible to load new definitions for React components and MST models and apply them to a running application.

In this lesson you will learn:
* How HMR roughly works
* How to accept changes to components
* How to accept changes to changing model definitions, while keeping state

Restore the Model Tree State using Hot Module Reloading when Model Definitions Change

It is time to give our wishlist app some more depth. In this lesson, we will introduce the concept of groups and users. So that we can manage multiple users inside a group that can have a wishlist. Also, we will take a quick look at powerful features like union types and type discrimination.

In this lesson you will learn:
* Using the type map to store data by key
* Using literals to create single value types
* Combining literals and unions to do type discrimination
* Using Quokka as scratchpad for quick coding experiments
* Using enumerations
* Enumerations are just sugar for a union of literals 

More mobx-state-tree Types: map, literal, union, and enumeration

In real life scenarios, many operations on our data are asynchronous. For example, because additional recourses need to get fetched. MST has first class support for asynchronous actions. We will start with a naively implemented async process, and work through async / await towards MST flows and generators.

In this lesson, you will learn
* That async process is painful if they need to respect the 'only actions can modify' semantics of MST
* Flows are the idiomatic way to describe async processes in MST
* Flows are robust; they make it possible to get full control over the lifecycle of a process

Defining Asynchronous Processes Using Flow

MST stores all data in a tree, where each piece of data lives at one unique location. In most state management solutions, this means you need to introduce weakly typed, primitive 'foreign keys' to refer to other parts of the state tree. But in MST you can leverage the concepts of references and identifiers to relate model instances to each other. MST will do the normalization behind the scenes for you.

In this lesson you will learn:
* The use of types.identifier to uniquely identify an instance of a specific type
* The use of types.reference to refer to data in another part of the tree, and with which you can interact with in another part of the tree
* The use of types.maybe to make as ".. or null" type
* Using types.late to create circular type definitions

Create Relationships in your Data with mobx-state-tree Using References and Identifiers

Let's stop hardcoding our initial state and fetch it from the server instead. 

In this lesson you will learn:
* Set up basic data fetching
* Leverage the `afterCreate` lifecycle hook to automatically run any setup logic a model instance needs to do after creation


Loading Data from the Server

MST has a pretty unique feature: It allows you to capture private state on models, and manage this state by using lifecycle hooks. For example by setting up a WebSocket connection and disposing of the connection automatically as soon as the instance gets removed from the store. In this lesson, we will leverage cancellable fetches to abort in-flight requests when appropriate

In this lesson you will learn:
* Aborting window.fetch requests :-).
* Storing private, volatile, internal state in the function closure
* A second life-cycle hook: beforeDestroy

Use Volatile State and Lifecycle Methods to Manage Private State

Let's make sure our changes get persisted. We will use the window.fetch api to store our changes in the json-server. And onSnapshot to do this automatically


Automatically Send Changes to the Server by Using onSnapshot

Since MST offers a runtime type system, it can create and compose types on the fly, making it possible to reuse logic in new and powerful ways.

In this lesson you will learn:
* That MST types are immutable and composed together behind the scenes
* How to compose types explicitly by using `types.compose`
* How to create dynamic, parameterized types by leveraging that MST types are first class javascript citizens

Manage Application State with Mobx-state-tree

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