Default shouldEmitPatchOnChange to false

README.md

@@ -510,7 +510,7 @@ const readOnlyExample = TransformExample.createReadOnly(snapshot);
 readOnlyExample.withoutParams; // => URL { href: "https://example.com" }
 ```
 
-Snapshotted views emit patches when their values change. If you don't want snapshotted views to emit a patch when they change, you can pass a `shouldEmitPatchOnChange` function that returns `false` to the `@snapshottedView`, or you can pass `false` to `setDefaultShouldEmitPatchOnChange` to disable patch emission for all snapshotted views.
+If your snapshotted views need to emit patches when their values change, you can pass a `shouldEmitPatchOnChange` function that returns `true` to the `@snapshottedView` decorator, or you can pass `true` to `setDefaultShouldEmitPatchOnChange` to enable patch emission for all snapshotted views.
 
 ##### Snapshotted view semantics
 

spec/__snapshots__/class-model-snapshotted-views.spec.ts.snap

@@ -1,30 +1,5 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`class model snapshotted views an observable instance emits a patch when the view value changes 1`] = `
-[MockFunction] {
-  "calls": [
-    [
-      {
-        "op": "replace",
-        "path": "/__snapshottedViewsEpoch",
-        "value": 1,
-      },
-      {
-        "op": "replace",
-        "path": "/__snapshottedViewsEpoch",
-        "value": 0,
-      },
-    ],
-  ],
-  "results": [
-    {
-      "type": "return",
-      "value": undefined,
-    },
-  ],
-}
-`;
-
 exports[`class model snapshotted views references references to models with snapshotted views can be instantiated 1`] = `
 {
   "examples": {

spec/class-model-snapshotted-views.spec.ts

@@ -72,27 +72,6 @@ describe("class model snapshotted views", () => {
     expect(instance.slug).toEqual("test");
   });
 
-  test("an observable instance emits a patch when the view value changes", () => {
-    const observableArray = observable.array<string>([]);
-
-    @register
-    class MyViewExample extends ClassModel({ key: types.identifier, name: types.string }) {
-      @snapshottedView()
-      get arrayLength() {
-        return observableArray.length;
-      }
-    }
-
-    const fn = jest.fn();
-    const instance = MyViewExample.create({ key: "1", name: "Test" });
-    onPatch(instance, fn);
-
-    runInAction(() => {
-      observableArray.push("a");
-    });
-    expect(fn).toMatchSnapshot();
-  });
-
   test("an observable instance's snapshot includes the snapshotted views epoch", () => {
     const instance = ViewExample.create({ key: "1", name: "Test" });
     expect(getSnapshot(instance)).toEqual({ __snapshottedViewsEpoch: 0, key: "1", name: "Test" });
@@ -236,7 +215,7 @@ describe("class model snapshotted views", () => {
 
     @register
     class Child extends ClassModel({}) {
-      @snapshottedView({ onError })
+      @snapshottedView({ onError, shouldEmitPatchOnChange: () => true })
       get parentsChildLength() {
         const parent: Parent = getParent(this, 2);
         return parent.children.size;
@@ -290,7 +269,7 @@ describe("class model snapshotted views", () => {
   describe("shouldEmitPatchOnChange", () => {
     afterEach(() => {
       // reset the default value
-      setDefaultShouldEmitPatchOnChange(true);
+      setDefaultShouldEmitPatchOnChange(false);
     });
 
     test("readonly instances don't use the shouldEmitPatchOnChange option", () => {
@@ -356,9 +335,15 @@ describe("class model snapshotted views", () => {
       });
 
       expect(onPatchFn).toHaveBeenCalled();
+      expect(onPatchFn.mock.calls).toEqual([
+        [
+          { op: "replace", path: "/__snapshottedViewsEpoch", value: 1 },
+          { op: "replace", path: "/__snapshottedViewsEpoch", value: 0 },
+        ],
+      ]);
     });
 
-    test("observable instances do emit a patch when shouldEmitPatchOnChange is undefined and setDefaultShouldEmitPatchOnChange hasn't been called", () => {
+    test("observable instances don't emit a patch when shouldEmitPatchOnChange is undefined and setDefaultShouldEmitPatchOnChange hasn't been called", () => {
       const observableArray = observable.array<string>([]);
 
       @register
@@ -378,7 +363,7 @@ describe("class model snapshotted views", () => {
         observableArray.push("a");
       });
 
-      expect(onPatchFn).toHaveBeenCalled();
+      expect(onPatchFn).not.toHaveBeenCalled();
     });
 
     test("observable instances do emit a patch when shouldEmitPatchOnChange is undefined and setDefaultShouldEmitPatchOnChange was passed true", () => {
@@ -404,6 +389,13 @@ describe("class model snapshotted views", () => {
       });
 
       expect(onPatchFn).toHaveBeenCalled();
+      expect(onPatchFn).toHaveBeenCalled();
+      expect(onPatchFn.mock.calls).toEqual([
+        [
+          { op: "replace", path: "/__snapshottedViewsEpoch", value: 1 },
+          { op: "replace", path: "/__snapshottedViewsEpoch", value: 0 },
+        ],
+      ]);
     });
 
     test("observable instances don't emit a patch when shouldEmitPatchOnChange is undefined and setDefaultShouldEmitPatchOnChange was passed false", () => {

src/class-model.ts

@@ -560,7 +560,7 @@ export const isClassModel = (type: IAnyType): type is IClassModelType<any, any,
   return (type as any).isMQTClassModel;
 };
 
-let defaultShouldEmitPatchOnChange = true;
+let defaultShouldEmitPatchOnChange = false;
 
 /**
  * Sets the default value for the `shouldEmitPatchOnChange` option for