# Using GoJS with Angular

Examples of most of the topics discussed on this page can be found in the gojs-angular-basic project, which serves as a simple starter project.

If you are new to GoJS, it may be helpful to first visit the Getting Started Tutorial .

The easiest way to get a component set up for a GoJS Diagram is to use the gojs-angular package, which exports Angular Components for GoJS Diagrams, Palettes, and Overviews. More information about the package, including the various props it takes, can be found on the NPM page. Examples here will be using a GraphLinksModel, but any model can be used.

Note: This page is assumes use of `gojs-angular` version 2.0+. Click here for a discussion on upgrading to version 2.0.

## General Information

### Installation

To use the published components, make sure you install GoJS and gojs-angular: `npm install gojs gojs-angular`.

### About Component Styling

Whether you are using a Diagram, Palette, or Overview `gojs-angular` component, you will probably want to style them. First, you'll need to style a CSS class for the div of your GoJS Diagram / Palette / Overview such as:

    /* app.component.css */
    .myDiagramDiv {
      background: whitesmoke;
      width: 800px;
      height: 300px;
      border: 1px solid black;
    }

To style the GoJS Diagram / Palette / Overview div, which will reside in the `gojs-angular` component(s) you are using, make sure you set the `@Component` decorator's `encapsulation` property to either `ViewEncapsulation.None` or `ViewEncapsulation.ShadowDown`. Without this, your styling will not effect the component divs. Read more about Angular view encapsulation here.

Your `@Component` decorator for the component holding the your GoJS / Angular Component(s) should look something like:

    @Component({
      selector: 'app-root',
      templateUrl: './app.component.html',
      styleUrls: ['./app.component.css'],
      encapsulation: ViewEncapsulation.None
    })

Note: You may alternatively use the default `ViewEncapsulation.Emulated` value, if you assign additional CSS modifiers :host and ::ng-deep to your class selector. Be warned, however, ng-deep is technically deprecated, so this is not best practice.

## The DataSyncService

The `gojs-angular` package comes with an Angular service called DataSyncService, used to easily merge changes (a go.IncrementalData instance) with an Array of Node or Link Data, or a modelData object.

This service has three static functions:

- `syncNodeData(changes, array)` - Merges any node data changes in a go.IncrementalData object with a given array of node data, then returns the new array
- `syncLinkData(changes, array)` - Merges any link data changes in a go.IncrementalData object with a given array of link data, then returns the new array. Note: Ensure you set the linkKeyProperty if you are using GraphLinksModel, so data merging is possible.
- `syncModelData(changes, object)` - Merges any modelData changes in a go.IncrementalData object with a given modelData object, then returns the new object

These functions should allow you to keep your data synced up as needed, without needing to write lots of code.

### Listening for Model Changes

It is common to listen for data changes in a Diagram or Palette, then do something with those changes on an application-level (such as syncing those changes with app-level data). That's why, for both the DiagramComponent and PaletteComponent, there is a `modelChange` `@Input` property function. This is a prime example of where the DataSyncService can be used.

As of `gojs-angular` 2.0, Array / object `@Input` properties are assumed to be immutable. As such, when updating these properties, new Arrays / objects must be generated -- one cannot simply mutate an element of the Array or object. Please see the gojs-angular-basic project for examples of both maintaining state immutability and usage of the DataSyncService.

Note: The UndoManager should always be enabled to allow for transactions to take place, but its maxHistoryLength can be set to 0 to prevent undo and redo.

## The Diagram and Palette Components

The Diagram and Palette Components accept a similar set of `@Input` properties.

Diagram Component accepts:

- `initDiagram` - A function that must return a GoJS Diagram. You may define your Diagram's Node and Link templates here.
- `divClassName` - A class name for your Diagram div
- `nodeDataArray` - An array containing data objects for your nodes
- `linkDataArray` - An array containing data objects for your links. Optional.
- `modelData` - A data object, containing your diagram's model.modelData. Optional.
- `skipsDiagramUpdate` - A boolean flag, specifying whether the component should skip updating, often set when updating state from a GoJS model change.
- `modelChange` - A function, which accepts a go.IncrementalData object. This function will fire when your Diagram's model changes, allowing you to decide what to do with those changes. A common practice is to sync your app-level data to reflect the changes in the diagram model, which is made simple using the DataSyncService `gojs-angular` ships with.

The Palette Component accepts:

- `initPalette` - A function that must return a GoJS Palette. You may define your Palette's Node and Link templates here.
- `divClassName` - A class name for the div your Palette div
- `nodeDataArray` - An array containing data objects for your nodes
- `linkDataArray` - An array containing data objects for your links. Optional.
- `modelData` - A data object, containing your palette's model.modelData. Optional.

Because GoJS Palettes are read-only by default, there is no `modelChange` property in PaletteComponent. Since there won't be user-driven changes to a Palette's model, changes to node/link/model data should be achieved by immutably altering the analogous above @Input properties.

## Sample Diagram / Palette Component Usage

Here is an example of how one might set up their Diagram / Palette component properties

    // Big object that holds app-level state data
    // As of gojs-angular 2.0, immutability is required of state for change detection
    public state = {
      // Diagram state props
      diagramNodeData: [
        { id: 'Alpha', text: "Alpha", color: 'lightblue' },
        { id: 'Beta', text: "Beta", color: 'orange' }
      ],
      diagramLinkData: [
        { key: -1, from: 'Alpha', to: 'Beta' }
      ],
      diagramModelData: { prop: 'value' },
      skipsDiagramUpdate: false,

      // Palette state props
      paletteNodeData: [
        { key: 'PaletteNode1', color: 'firebrick' },
        { key: 'PaletteNode2', color: 'blueviolet' }
      ]
    }; // end state object

    public diagramDivClassName: string = 'myDiagramDiv';
    public paletteDivClassName = 'myPaletteDiv';

    // initialize diagram / templates
    public initDiagram(): go.Diagram {
      const dia = new go.Diagram({
        'undoManager.isEnabled': true,
        model: new go.GraphLinksModel(
          {
            nodeKeyProperty: 'id',
            linkKeyProperty: 'key' // IMPORTANT! must be defined for merges and data sync when using GraphLinksModel
          }
        )
      });

      // define the Node template
      dia.nodeTemplate =
        new go.Node('Auto')
          .add(
            new go.Shape('RoundedRectangle', { stroke: null })
              .bind('fill', 'color'),
            new go.TextBlock({ margin: 8, editable: true })
              .bindTwoWay('text', 'text')
          );

      return dia;
    }

    /**
      * Handle GoJS model changes, which output an object of data changes via Mode.toIncrementalData.
      * This method should iterate over thoe changes and update state to keep in sync with the FoJS model.
      * This can be done with any preferred state management method, as long as immutability is preserved.
      */
    public diagramModelChange = function(changes: go.IncrementalData) {
      console.log(changes);
      // see gojs-angular-basic for an example model changed handler that preserves immutability
      // when setting state, be sure to set skipsDiagramUpdate: true since GoJS already has this update
    };

    public initPalette(): go.Palette {
      const palette = new go.Palette();

      // define the Node template
      palette.nodeTemplate =
        new go.Node('Auto')
          .add(
            new go.Shape('RoundedRectangle', { stroke: null })
              .bind('fill', 'color'),
            new go.TextBlock({ margin: 8 })
              .bind('text', 'key')
          );

      palette.model = new go.GraphLinksModel(
        {
          linkKeyProperty: 'key'  // IMPORTANT! must be defined for merges and data sync when using GraphLinksModel
        });

      return palette;
    }

Once you've defined your `@Input` properties for your components, pass these properties to your DiagramComponent and PaletteComponent in your template, like so:

    <gojs-diagram
      [initDiagram]='initDiagram'
      [nodeDataArray]='state.diagramNodeData'
      [linkDataArray]='state.diagramLinkData'
      [modelData]='state.diagramModelData'
      [skipsDiagramUpdate]='state.skipsDiagramUpdate'
      (modelChange)='diagramModelChange($event)'
      [divClassName]='diagramDivClassName'>
    </gojs-diagram>

    <gojs-palette
      [initPalette]='initPalette'
      [nodeDataArray]='state.paletteNodeData'
      [divClassName]='paletteDivClassName'>
    </gojs-palette>

You will now have a GoJS Diagram and Palette working in your Angular application. Again, for a full example of a `gojs-angular` application, see gojs-angular-basic.

#### A Note on Diagram Reinitialization

Occasionally you may want to treat a model update as if you were loading a completely new model. But initialization is only done in your `initDiagram` function, within the `DiagramComponent`'s `ngAfterViewInit` lifecycle hook, and only once. A regular model update is not treated as an initialization, so none of the `initial...` properties of your Diagram will apply.

To address this problem, `DiagramComponent` exposes a `clear` method. When called, it clears its diagram of all nodes, links, and model data, and prepares the next state update to be treated as a diagram initialization. That will result in an initial layout and perform initial diagram content alignment and scaling. Note that `initDiagram` is not called again.

Here is a small sample of how one might trigger diagram reinitilization using the `clear` method with `gojs-angular` 2.0.

    public reinitModel() {
        this.myDiagramComponent.clear();
        this.state = produce(this.state, draft => {
            draft.skipsDiagramUpdate = false;
            draft.diagramNodeData = [{ id: "Alpha", text: "Zorro", color: "red" }];
            draft.diagramLinkData = [];
        });
    }

## Using the Overview Component

The Overview Component accepts the following Angular `@Input()` properties.

- `initOverview` - A function that must return a GoJS Overview.
- `divClassName` - A class name for your Overview div
- `observedDiagram` - The GoJS Diagram this Overview observes

Define these properties in the component that will hold your Overview Component, like:

    public oDivClassName = 'myOverviewDiv';
    public initOverview(): go.Overview {
      return new go.Overview();
    }
    public observedDiagram = null;

Then pass these properties to your Overview Component in your template, like:

    <gojs-overview
      [initOverview]='initOverview'
      [divClassName]='oDivClassName'
      [observedDiagram]='observedDiagram'>
    </gojs-overview>

But, we're not done yet. `observedDiagram` is null, so the Overview won't observe anything. To assign your Overview a Diagram to observe, you will have to reassign the `observedDiagram` property after initialization. To do so, reassign the bound `observedDiagram` property in your component holding your Overview Component in the `ngAfterViewInit` lifecycle hook.

Note: To avoid a `ExpressionChangedAfterItHasBeenCheckedError`, you must inform Angular to then detect changes. This can be done with the ChangeDetectorRef.detectChanges() method. You can inject a ChangeDetectorRef instance into your wrapper Component constructor, and use that after you alter `observedDiagram` to call detectChanges(). Like so:

    constructor(private cdr: ChangeDetectorRef) { }

    public ngAfterViewInit() {
      if (this.observedDiagram) return;
      // in this snippet, this.myDiagramComponent is a reference to a GoJS/Angular Diagram Component
      // that has a valid GoJS Diagram
      this.observedDiagram = this.myDiagramComponent.diagram;

      // IMPORTANT: without this, Angular will throw ExpressionChangedAfterItHasBeenCheckedError (dev mode only)
      this.cdr.detectChanges();
    }

Now, after initialization, your Overview should display appropriately.

## Updating Properties Based on App State

You may have some app-level properties you want to affect the behavior / appearance of your Diagram, Palette, or Overview. You could subclass their respective components and add `@Input` bindings with specific setter methods, or, more simply, you can have an `ngOnChanges` function in your app-level component that updates various Diagram / Palette / Component properties based on your app state.

For example, say you have an app-level property called `showGrid`. When `showGrid` is true, your Diagram's grid should be visible -- when false, it should be invisible. In your AppComponent, you could do something like:

    // myDiagramComponent is a reference to your DiagramComponent
    @ViewChild('myDiagram', { static: true }) public myDiagramComponent: DiagramComponent;

    public ngOnChanges () {
      // whenever showGrid changes, update the diagram.grid.visible in the child DiagramComponent
      if (this.myDiagramComponent && this.myDiagramComponent.diagram instanceof go.Diagram) {
        this.myDiagramComponent.diagram.grid.visible = this.showGrid;
      }
    }

## Migrating to 2.0

This page assumes use of `gojs-angular` version 2.0, which requires immutable state, unlike version 1.0. It is recommended to use the 2.0 version. If you have a `gojs-angular` project using version 1.x and want to upgrade, reference this section for tips on migrating to version 2.

### Should I Upgrade?

In general, yes.

If you have very simple node and link data, using the latest 1.x version might be okay. But new features and quality of life changes will be published on the 2.x branch moving forward.

Version 2.0 handles complex nested data much better than the previous version, due to its focus on immutable data. Additionally, it is a bit smaller in file size.

One may wish to hold off on upgrading if they have lots of operations mutating their `@Input` properties, and they do not want to take the time to rewrite those operations immutably. However, the guide below details one way one could do this. Our `gojs-angular-basic` sample also has demonstrations of immutably updating `@Input` properties to make such a rewrite easier.

### Upgrade gojs-angular Version

Update your `package.json` to require `gojs-angular` version 2.0 or greater, then run `npm install`

It is also recommended to upgrade to the latest version of `gojs`.

### Immutability

The biggest change with 2.0 is you must enforce immutability of `@Input` properties to your Diagram and Palette components.

So, for instance, whenever an entry of `diagramNodeData` is updated, removed, or changed, you will need to generate a whole new Array for `DiagramComponent.diagramNodeData`. This can be done in many different ways with many different packages. A popular choice is immer, which exposes a `produce` function that allows one to immutability manipulate their data on a `draft` variable. We will use that function here for demonstration purposes.

#### The Version 1.0 Way

In `gojs-angular` version 1, if you wanted to add some node data to your `diagramNodeData` `@Input` property, you could do so by simply adding to the `diagramNodeData`, mutating it. Such as:

    public addNode = function(nodeData: go.ObjectData) {
      // sync changes with GoJS model
      this.skipsDiagramUpdate = false;
      this.diagramNodeData.push(nodeData);
    };

#### The Version 2.0 Way

In `gojs-angular` version 2, that same `addNode` function must be changed so the `diagramNodeData` property is updated immutably (that is, replaced with an entirely new Array). Here is an example of doing that with immer's `produce` function.

    public addNode = function(nodeData: go.ObjectData) {
      this.state = produce(this.state, draft => {
        const nodedata = { id: "Zeta", text: "Zorro", color: "red" };
        draft.skipsDiagramUpdate = false;
        draft.diagramNodeData.push(nodedata);
      });
    }

Notice we are also using a massive `state` object to hold `gojs-angular` component properties. This makes these kinds of immutable operations (especially if you are using immer, or a package like it) straightforward (see how we were able to update both `skipsDiagramUpdate` and `diagramNodeData` on the same `draft` variable).

To see more samples of enforcing immutability with `gojs-angular`, see gojs-angular-basic, particularly the `modelChange` property of the Diagram Component.

### Additional Considerations

Additionally, PaletteComponent no longer supports `skipsPaletteUpdate` or `modelChange` properties. As GoJS Palettes are read-only by default, their models should not be changing based on user input. Instead, if you need to update their node/link/model data, update their `@Input` properties (immutably, of course).