Add methods getOrDefault and getOrThrow

src/Model/collections.ts

@@ -2,6 +2,7 @@ import { Doc } from './Doc';
 import { Model, RootModel } from './Model';
 import { JSONObject } from 'sharedb/lib/sharedb';
 import type { Path, ReadonlyDeep, ShallowCopiedValue, Segments } from '../types';
+
 var LocalDoc = require('./LocalDoc');
 var util = require('../util');
 
@@ -75,6 +76,21 @@ declare module './Model' {
     getOrCreateCollection(name: string): Collection;
     getOrCreateDoc(collectionName: string, id: string, data: any);
 
+    /**
+     * Get a value that may be undefined but ensure value is returned
+     *
+     * @param subpath
+     * @param defaultValue value to return if no value at subpath
+     */
+    getOrDefault<S>(subpath: Path, defaultValue: S): ReadonlyDeep<S>;
+
+    /**
+     * Get a value and throw error if undefined
+     *
+     * @param subpath
+     */
+    getOrThrow<S>(subpath: Path): ReadonlyDeep<S>;
+
     _get(segments: Segments): any;
     _getCopy(segments: Segments): any;
     _getDeepCopy(segments: Segments): any;
@@ -152,6 +168,19 @@ Model.prototype.getOrCreateDoc = function(collectionName, id, data) {
   return collection.getOrCreateDoc(id, data);
 };
 
+Model.prototype.getOrDefault = function<S>(subpath: Path, defaultValue: S) {
+  return this.get(subpath) ?? defaultValue as ReadonlyDeep<S>;
+};
+
+Model.prototype.getOrThrow = function<S>(subpath?: Path) {
+  const value = this.get(subpath);
+  if (value === undefined) {
+    const fullpath = [this._at, subpath].filter(Boolean).join('.');
+    throw new Error(`No value at path ${fullpath}`)
+  }
+  return value;
+};
+
 /**
  * @param {String} subpath
  */

test/Model/collections.js

@@ -0,0 +1,37 @@
+const {expect} = require('../util');
+const {RootModel} = require('../../lib');
+
+describe('collections', () => {
+  describe('getOrDefault', () => {
+    it('returns value if defined', () => {
+      const model = new RootModel();
+      model.add('_test_doc', {name: 'foo'});
+      const value = model.getOrDefault('_test_doc', {name: 'bar'});
+      expect(value).not.to.be.undefined;
+    });
+
+    it('returns defuault value if undefined', () => {
+      const model = new RootModel();
+      const defaultValue = {name: 'bar'};
+      const value = model.getOrDefault('_test_doc', defaultValue);
+      expect(value).not.to.be.undefined;
+      expect(value.name).to.equal('bar');
+      expect(value).to.eql(defaultValue);
+    });
+  });
+
+  describe('getOrThrow', () => {
+    it('returns value if defined', () => {
+      const model = new RootModel();
+      model.add('_test_doc', {name: 'foo'});
+      const value = model.getOrThrow('_test_doc', {name: 'bar'});
+      expect(value).not.to.be.undefined;
+    });
+
+    it('thows if value undefined', () => {
+      const model = new RootModel();
+      expect(() => model.getOrThrow('_test_doc', {name: 'bar'})).to.throw(`No value at path _test_doc`);
+      expect(() => model.scope('_test').getOrThrow('doc.1', {name: 'bar'})).to.throw(`No value at path _test.doc.1`);
+    });
+  });
+});