How To Split Mobx State Tree Models Across Multiple Files?

user_977286 0
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I have a Mobx State Tree model that has grown too long and I would like to split it across multiple javascript files.

Here is a demo of some of the code:

///file1.js
 import { types } from "mobx-state-tree";

export const ExampleModel = types
.model("Example", {
    id: types.identifier,
    name: types.optional(types.string, ""),
    anotherName: types.optional(types.string, ""),

})
.views(self => ({
    get test() {
        return "test"
    }
}))
.views(self => ({
    get anotherTest() {
        return "anotherTest"
    }
}))
.actions(self => ({
    setName(name) {
        self.name = name
    }
}))
.actions(self => ({
    setAnotherName(name) {
        self.anotherName = name
    }
}))

What I want is to split this between two files, like:

///file1.js
import { types } from "mobx-state-tree";

export const ExampleModel = types
.model("Example", {
    id: types.identifier,
    name: types.optional(types.string, ""),
    anotherName: types.optional(types.string, ""),

})
.views(self => ({
    get test() {
        return "test"
    }
})) 
.actions(self => ({
    setName(name) {
        self.name = name
    }
}))


///file2.js
import { ExampleModel } from "./file1.js";
ExampleModel.views(self => ({
    get anotherTest() {
        return "anotherTest"
    }
})).actions(self => ({
    setAnotherName(name) {
        self.anotherName = name
    }
}))

You can see here that I am attempting to move a view and and action to a separate javascript file. I expect I need to do some kind of import and export between these two files, but I can't figure out how to do it.

I know that Mobx State Tree has compose functionality, as shown here: https://nathanbirrell.me/notes/composition-mobx-state-tree/

But I am afer something more simple than this... I don't want to set up multiple models, I just need the ability to spread a model across multiple javascript files.

mobx-state-tree
2 Answers

We do that all the time.

Just export your actions and views separately:

// file1.js
import { types } from "mobx-state-tree"

export const props = {
    id: types.identifier,
    name: types.optional(types.string, ""),
    anotherName: types.optional(types.string, ""),

}
export const views = self => ({
    get test() {
        return "test"
    }
})
export const actions = self => ({
    setName(name) {
        self.name = name
    }
})

Then, create the final store from them:

// store.js
import { types } from "mobx-state-tree"
import * as file1 from "./file1"
import * as file2 from "./file2"

const Store = types
  .model('Store')
  .props(file1.props)
  .views(file1.views)
  .actions(file1.actions)
  .props(file2.props)
  .views(file2.views)
  .actions(file2.actions)

export default Store

You can also create your own stores for testing, only from one file:

// __tests__/file1.js
import { types } from "mobx-state-tree"
import { actions, views, props } from "./file1"

const Store = types
  .model('Store')
  .props(props)
  .views(views)
  .actions(actions)
const store = Store.create(myTestSnapshot)

test('setName should set the name prop', () => {
  store.setName('john')
  expect(store.name).toBe('john')
})
user_18305740

Expressive, flexible and easy model composition is one of the best features in mobx-state-tree! :) Here are two examples, taken straight from the relevant section in the docs:

const Square = types
    .model("Square", {
        width: types.number
    })
    .views(self => ({
        surface() {
            return self.width * self.width
        }
    }))

// create a new type, based on Square
const Box = Square
    .named("Box")
    .views(self => {
        // save the base implementation of surface
        const superSurface = self.surface
        return {
            // super contrived override example!
            surface() {
                return superSurface() * 1
            },
            volume() {
                return self.surface * self.width
            }
        }
    }))

// no inheritance, but, union types and code reuse
const Shape = types.union(Box, Square)

And another one:

const CreationLogger = types.model().actions(self => ({
    afterCreate() {
        console.log("Instantiated " + getType(self).name)
    }
}))

const BaseSquare = types
    .model({
        width: types.number
    })
    .views(self => ({
        surface() {
            return self.width * self.width
        }
    }))

export const LoggingSquare = types
    .compose(
        // combine a simple square model...
        BaseSquare,
        // ... with the logger type
        CreationLogger
    )
    // ..and give it a nice name
    .named("LoggingSquare")

Applying that to your needs: Square and Box can be in different files, where Box.js imports Square from Square.js in the first example.

Same exact technique can be applied to the second example.

user_9158750
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