docs: include filter

docs/site/Include-filter.md

@@ -2,9 +2,272 @@
 title: 'Include filter'
 lang: en
 keywords: LoopBack 4.0, LoopBack 4, include
-layout: readme
-source: loopback-next
-file: packages/metadata/README.md
 sidebar: lb4_sidebar
 permalink: /doc/en/lb4/Include-filter.html
----
+---
+
+An *include* filter enables you to include results from related models in a
+query over relations. (See [Relations](Relations.md) for details on how to
+define relations)
+
+The value of the include filter can be a string, an array, or an object.
+
+{% include important.html content="You can use an _include_ filter with `find(),` `findOne()` and `findById()` methods.
+" %}
+
+### Node.js API
+
+{% include content/angular-methods-caveat.html lang=page.lang %}
+
+To query one relation:
+
+```ts
+{
+  include: [{relation: 'relationName'}];
+}
+```
+
+To query multiple relations:
+
+```ts
+{
+  include: [{relation: 'relationName1'}, {relation: 'relationName2'}];
+}
+```
+
+To query nested relations, use the scope field:
+
+```ts
+{
+    relation: 'relationName',
+    scope: {
+    include: [{relation: 'nestedRelationName'}],
+    },
+}
+```
+
+Where:
+
+- _relationName_ is the name of a relation defined in repositories. Check
+  [Relations](Relations.md) for details.
+
+### REST API
+
+To query one relation: `/modelName?filter[include][][relation]=_relationName_`
+
+To query multiple relations:
+`/modelName?filter[include][0][relation]=_relationName1_&filter[include][1][relation]=_relationName2_`
+
+To query nested relations, as the url would get too long, we recommend to encode
+it with `encodeURIComponent(JSON.stringify(filter))`:
+`/modelName?filter=<encodeResult>`
+
+You can also use
+[stringified JSON format](Querying-data.md#using-stringified-json-in-rest-queries) in
+a REST query.
+
+### Examples
+
+- Return all customers with their orders:
+
+{% include code-caption.html content="Node.js API" %}
+
+```ts
+await customerRepository.find({include: [{relation: 'orders'}]});
+```
+
+{% include code-caption.html content="REST" %}
+
+`/customers?filter[include][][relation]=orders`
+
+Or stringified JSON format:
+
+`/customers?filter={"include":[{"relation":"orders"}]}`
+
+Result:
+
+```ts
+[{
+    id: 1,
+    name: 'Tom Nook',
+    orders:[{id: 1, desc: 'pencil'}]
+ },
+ {...}
+]
+```
+
+- Return all customers with their orders and their address:
+
+{% include code-caption.html content="Node.js API" %}
+
+```ts
+await customerRepository.find({
+  include: [{relation: 'orders'}, {relation: 'address'}],
+});
+```
+
+{% include code-caption.html content="REST" %}
+
+`/customers?filter[include][0][relation]=orders?filter[include][1][relation]=address`
+
+Result:
+
+```ts
+[{
+    id: 1,
+    name: 'Tom Nook',
+    orders:[{id: 1, desc: 'pencil'}],
+    address: {'8200 Warden Ave'}
+ },
+ {...}
+]
+```
+
+- Return all customers with their orders and also the shipment information of
+  orders:
+
+{% include code-caption.html content="Node.js API" %}
+
+```ts
+await customerRepository.find({
+  include: [
+    {
+      relation: 'orders',
+      scope: {
+        include: [{relation: 'shipment'}],
+      },
+    },
+  ],
+});
+```
+
+{% include code-caption.html content="REST" %}
+
+(using `encodeURIComponent`)
+
+```
+/customers?filter=%7B"include"%3A%5B%7B"relation"%3A"orders"%2C"scope"%3A%7B"include"%3A%5B%7B"relation"%3A"shipment"%7D%5D%7D%7D%5D%7D
+```
+
+Result:
+
+```ts
+[{
+    id: 1,
+    name: 'Tom Nook',
+    orders:[
+        {id: 123,
+        desc: 'pencil',
+        shipment: {id: 999, company: 'UPS'} // nested related models
+        }
+    ],
+ },
+ {...}
+]
+```
+
+#### Combined use of `fields` and `include` for a `belongsTo` relation
+
+If you want to use both `include` and [`fields`](Fields-filter.md) to display
+only specific fields of a model and a specific belongsTo relation, **you need to
+add the relation foreign key in the `fields`** :
+
+Return all posts only with field `title` and the relation `category`:
+
+```ts
+await postRepository.find({include: [{relation: 'category'}], fields: ['title', 'categoryId'});
+```
+
+#### Include with filters
+
+In some cases, you may want to apply filters to related models to be included.
+
+{% include note.html content="
+
+When you apply filters to related models, the query returns results from the
+first model plus any results from related models with the filter query, similar
+to a \"left join\" in SQL.
+
+" %}
+
+LoopBack supports that with the following syntax (for example):
+
+```ts
+await postRepository.find({
+  include: [
+    {
+      relation: 'owner', // include the owner object
+      scope: {
+        // further filter the owner object
+        fields: ['username', 'email'], // only show two fields
+        include: {
+          // include orders for the owner
+          relation: 'orders',
+          scope: {
+            where: {orderId: 5}, // only select order with id 5
+          },
+        },
+      },
+    },
+  ],
+});
+```
+
+For real-world scenarios where only users in `$authenticated` or `$owner` roles
+should have access, use `findById()`. For example, the following example uses
+filters to perform pagination:
+
+```ts
+await postRepository.findById('123', {
+  include: [
+    {
+      relation: 'owner',
+      scope: {
+        // fetch 1st "page" with 5 entries in it
+        skip: 0,
+        limit: 5,
+      },
+    },
+  ],
+});
+```
+
+#### Access included objects
+
+In the Node.js API, you can simply access the returned model instance with
+related items as a plain JSON object. For example:
+
+```ts
+const result = await postRepository.find({
+  include: [{relation: 'owner'}, {relation: 'orders'}],
+});
+console.log(result[0].owner, result[0].orders);
+// log the related owner and order of the first returned instance
+```
+
+Note the relation properties such as `post.owner` reference a JavaScript
+**function** for the relation method.
+
+#### REST examples
+
+These examples assume a customer model with a hasMany relationship to a reviews
+model.
+
+Return all customers including their reviews:
+
+`/customers?filter[include][][relation]=reviews`
+
+Return all customers including their reviews and also their orders:
+
+`/customers?filter[include][0][relation]=reviews?filter[include][1][relation]=orders`
+
+Return all customers whose age is 21, including their reviews:
+
+`/customers?filter[include][][relation]=reviews&filter[where][age]=21`
+
+Return first two customers including their reviews:
+
+`/customers?filter[include][][relation]=reviews&filter[limit]=2`
+
+**See also**:
+[Querying related models](HasMany-relation.md#querying-related-models).