Add an example of a foreign key relationship.

This adds a `DB` example that contains a number of tables each of
which have rows that link to each other. This uses the ability to link
anywhere in the store to create a factory method that creates entities
elswhere in the store.

In this example, the `Blog` record has a reference to a `Person` which
is the author. The factory for author attribute of a blog, creates
that person in the database, and then returns that person.

Author: cowboyd

examples/db.js

@@ -0,0 +1,142 @@
+import { append, map, foldl } from 'funcadelic';
+import { NumberType, StringType } from './types';
+import { create as _create } from '../index';
+import { view, At } from '../src/lens';
+import { link, valueOf, pathOf, atomOf, typeOf, metaOf, ownerOf } from '../src/meta';
+
+import faker from 'faker';
+
+class Person {
+  firstName = StringType;
+  lastName = StringType;
+}
+
+class Blog {
+  title = StringType;
+  author = belongsTo(Person, "people");
+}
+
+class Comment {}
+
+function Table(Type, factory = {}) {
+
+  return class Table {
+    static Type = Type;
+    static name = `Table<${Type.name}>`;
+
+    nextId = NumberType;
+
+    get length() { return Object.keys(this.records).length; }
+
+    get latest() { return this.records[this.latestId]; }
+
+    get latestId() { return this.nextId.state - 1; }
+
+    get records() {
+      return map((value, key) => ln(Type, pathOf(this).concat(["records", key]), this), this.state.records);
+    }
+
+    get state() {
+      return valueOf(this) || { nextId: 0, records: {}};
+    }
+
+    create(overrides = {}) {
+      let id = this.nextId.state;
+      let record = createAt(this.nextId.increment(), Type, ["records", id], { id });
+
+      let created = foldl((record, { key, value: attr }) => {
+        if (record[key]) {
+          let attrFn = typeof attr === 'function' ? attr : () => attr;
+
+          // create a local link of the DB that returns itself. to pass into
+          // the factory function.
+          let db = link(_create(DB), DB, pathOf(this).slice(0, -1), atomOf(record));
+
+          let result = attrFn(overrides[key], db);
+
+          let next = metaOf(result) ? link(record, Type, pathOf(record), atomOf(result)) : record;
+
+          return next[key].set(result);
+        } else {
+          return record;
+        }
+      }, record, append(factory, overrides));
+
+      let owner = ownerOf(this);
+      return link(this, typeOf(this), pathOf(this), atomOf(created), owner.Type, owner.path);
+    }
+  };
+}
+
+
+
+class DB {
+  people = Table(Person, {
+    firstName: () => faker.name.firstName(),
+    lastName: () => faker.name.lastName()
+  });
+  blogs = Table(Blog, {
+    title: () => faker.random.words(),
+    author: (attrs, db) => {
+      return db.people.create(attrs)
+        .people.latest;
+    }
+  });
+  comments = Table(Comment);
+}
+
+function createAt(parent, Type, path, value) {
+  return link(_create(Type), Type, pathOf(parent).concat(path), atomOf(parent)).set(value);
+}
+
+function ln(Type, path, owner) {
+  return link(_create(Type), Type, path, atomOf(owner), typeOf(owner), pathOf(owner));
+}
+
+import Relationship from '../src/relationship';
+
+function linkTo(Type, path) {
+  return new Relationship(resolve);
+
+  function resolve(origin, originType, originPath /*, relationshipName */) {
+
+    return {
+      Type,
+      path: path.reduce((path, element) => {
+        if (element === '..') {
+          return path.slice(0, -1);
+        } else if (element === '.') {
+          return path;
+        } else {
+          return path.concat(element);
+        }
+      }, originPath)
+    };
+  }
+}
+
+function belongsTo(T, tableName) {
+  return new Relationship(resolve);
+
+  function BelongsTo(originType, originPath, foreignKey) {
+    return class BelongsTo extends T {
+      set(value) {
+        let origin = ln(originType, originPath, value);
+        let id = valueOf(value).id;
+        return origin.set(append(valueOf(origin), {
+          [foreignKey]: id
+        }));
+      }
+    };
+  }
+
+  function resolve(origin, originType, originPath, relationshipName) {
+    let foreignKey = `${relationshipName}Id`;
+    let id = view(At(foreignKey), valueOf(origin));
+    let Type = BelongsTo(originType, originPath, foreignKey);
+    let { resolve } = linkTo(Type, ["..", "..", "..", tableName, "records", id]);
+    return resolve(origin, originType, originPath, relationshipName);
+  }
+}
+
+export default _create(DB, {});

examples/types.js

@@ -0,0 +1,28 @@
+import { valueOf } from '../index';
+
+export class NumberType {
+
+  get state() {
+    return valueOf(this) || 0;
+  }
+
+  initialize(value) {
+    if (value == null) {
+      return 0;
+    } else if (isNaN(value)) {
+      return this;
+    } else {
+      return Number(value);
+    }
+  }
+
+  increment() {
+    return this.state + 1;
+  }
+}
+
+export class StringType {
+  get state() {
+    return valueOf(this) || '';
+  }
+}

index.js

@@ -2,4 +2,4 @@ import create from './src/create';
 import Identity from './src/identity';
 
 export { create, Identity };
-export { valueOf, metaOf, atomOf } from './src/meta';
+export { valueOf, metaOf, atomOf, pathOf } from './src/meta';

package.json

@@ -26,14 +26,17 @@
   },
   "devDependencies": {
     "@babel/core": "7.1.6",
+    "@babel/plugin-proposal-class-properties": "^7.1.0",
+    "@babel/polyfill": "^7.0.0",
     "@babel/preset-env": "^7.0.0",
     "@babel/register": "^7.0.0",
-    "@babel/polyfill": "^7.0.0",
     "babel-eslint": "^10.0.1",
     "coveralls": "3.0.2",
     "eslint": "^5.7.0",
     "eslint-plugin-prefer-let": "^1.0.1",
     "expect": "^23.4.0",
+    "faker": "^4.1.0",
+    "invariant": "^2.2.4",
     "mocha": "^5.2.0",
     "nyc": "13.1.0",
     "rollup": "^0.67.4",

src/meta.js

@@ -68,7 +68,11 @@ class Location {
 
 export const AtomOf = type(class AtomOf {
   atomOf(object) {
-    return this(object).atomOf(object);
+    if (object != null) {
+      return this(object).atomOf(object);
+    } else {
+      return undefined;
+    }
   }
 });
 

tests/db.test.js

@@ -0,0 +1,62 @@
+import expect from 'expect';
+
+import db from '../examples/db';
+import { valueOf } from '../index';
+
+describe('a referential DB', ()=> {
+  it('starts out empty', ()=> {
+    expect(db.people.length).toEqual(0);
+    expect(db.blogs.length).toEqual(0);
+    expect(db.comments.length).toEqual(0);
+  });
+
+  describe('creating a person with static attributes', ()=> {
+    let next;
+    let person;
+    beforeEach(()=> {
+      next = db.people.create({
+        firstName: 'Bob',
+        lastName: 'Dobalina'
+      });
+      person = next.people.latest;
+    });
+    it('contains the newly created person', ()=> {
+      expect(next.people.length).toEqual(1);
+      expect(person).toBeDefined();
+      expect(person.firstName.state).toEqual('Bob');
+      expect(person.lastName.state).toEqual('Dobalina');
+    });
+  });
+
+  describe('creating a person with higher order attributes', ()=> {
+    let next;
+    let person;
+    beforeEach(()=> {
+      next = db.people.create();
+      person = next.people.latest;
+    });
+
+    it('creates them with generated attributes', ()=> {
+      expect(person.firstName.state).not.toBe('');
+      expect(person.lastName.state).not.toBe('');
+    });
+  });
+
+  describe('creating a blog post with related author', ()=> {
+    let next;
+    let blog;
+
+    beforeEach(()=> {
+      next = db.blogs.create();
+      blog = next.blogs.latest;
+    });
+    it('has a related author', ()=> {
+      expect(blog.author).toBeDefined();
+    });
+    it('is the same as a person created in the people table', ()=> {
+      expect(next.people.latest).toBeDefined();
+      expect(valueOf(next.people.latest)).toBe(valueOf(next.blogs.latest.author));
+    });
+  });
+
+});

yarn.lock

@@ -1503,6 +1503,11 @@ extsprintf@^1.2.0:
   resolved "https://registry.yarnpkg.com/extsprintf/-/extsprintf-1.4.0.tgz#e2689f8f356fad62cca65a3a91c5df5f9551692f"
   integrity sha1-4mifjzVvrWLMplo6kcXfX5VRaS8=
 
+faker@^4.1.0:
+  version "4.1.0"
+  resolved "https://registry.yarnpkg.com/faker/-/faker-4.1.0.tgz#1e45bbbecc6774b3c195fad2835109c6d748cc3f"
+  integrity sha1-HkW7vsxndLPBlfrSg1EJxtdIzD8=
+
 fast-deep-equal@^1.0.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/fast-deep-equal/-/fast-deep-equal-1.1.0.tgz#c053477817c86b51daa853c81e059b733d023614"
@@ -1889,7 +1894,7 @@ inquirer@^6.1.0:
     strip-ansi "^4.0.0"
     through "^2.3.6"
 
-[email protected], invariant@^2.2.2:
+[email protected], invariant@^2.2.2, invariant@^2.2.4:
   version "2.2.4"
   resolved "https://registry.yarnpkg.com/invariant/-/invariant-2.2.4.tgz#610f3c92c9359ce1db616e538008d23ff35158e6"
   integrity sha512-phJfQVBuaJM5raOpJjSfkiD6BpbCE4Ns//LaXl6wGYtUBY83nWS6Rf9tXm2e8VaK60JEjYldbPif/A2B1C2gNA==