fix: an entity with relations can be created also without them

README.md

@@ -135,6 +135,18 @@ Creates an entity for the model.
 const user = db.user.create()
 ```
 
+When called without arguments, `.create()` will populate the entity properties using the getter functions you've specified in the model definition.
+
+You can also provide a partial initial values when creating an entity:
+
+```js
+const user = db.user.create({
+  firstName: 'John',
+})
+```
+
+> Note that all model properties _are optional_, including [relational properties](#model-relationships).
+
 #### `findFirst`
 
 Returns the first entity that satisfies the given query.

src/model/defineRelationalProperties.ts

@@ -36,6 +36,9 @@ export function defineRelationalProperties(
         `defining relational property "${entity.__type}.${property}"`,
         relation,
       )
+
+      if (!(property in initialValues)) return properties
+
       // Take the relational entity reference from the initial values.
       const entityRefs: Entity<any, any>[] = [].concat(initialValues[property])
 

test/relations/many-to-one.test.ts

@@ -110,3 +110,19 @@ test('supports querying through nested relational properties', () => {
 
   expect(result).toHaveLength(3)
 })
+
+test('should not throw error if an entity with many-to-one relation is created without it', () => {
+  const db = factory({
+    user: {
+      id: primaryKey(random.uuid),
+      firstName: name.firstName,
+    },
+    post: {
+      id: primaryKey(random.uuid),
+      title: random.words,
+      author: oneOf('user'),
+    },
+  })
+
+  expect(() => db.post.create()).not.toThrow()
+})

test/relations/one-to-many.test.ts

@@ -76,3 +76,18 @@ test('supports querying through one-to-many relation', () => {
   const userIds = users.map((user) => user.id)
   expect(userIds).toEqual(['user-1', 'user-3'])
 })
+
+test('should not throw error if an entity with one-to-many relation is created without it', () => {
+  const db = factory({
+    user: {
+      id: primaryKey(random.uuid),
+      posts: manyOf('post'),
+    },
+    post: {
+      id: primaryKey(random.uuid),
+      title: random.words,
+    },
+  })
+
+  expect(() => db.user.create()).not.toThrow()
+})

test/relations/one-to-one.test.ts

@@ -1,7 +1,7 @@
 import { random } from 'faker'
 import { factory, primaryKey, oneOf } from '@mswjs/data'
 
-test.only('supports one-to-one relation', () => {
+test('supports one-to-one relation', () => {
   const db = factory({
     country: {
       id: primaryKey(random.uuid),
@@ -57,3 +57,19 @@ test('supports querying through a one-to-one relational property', () => {
   })
   expect(capital).toHaveProperty('name', 'Washington')
 })
+
+test('should not throw error if an entity with one-to-one relation is created without it', () => {
+  const db = factory({
+    country: {
+      id: primaryKey(random.uuid),
+      name: random.words,
+    },
+    capital: {
+      id: primaryKey(random.uuid),
+      name: random.word,
+      country: oneOf('country'),
+    },
+  })
+
+  expect(() => db.capital.create()).not.toThrow()
+})