feat(231): adopt batch Get (#177)

Importing batch-get from aip.dev.
---------

Co-authored-by: Richard Frankel <[email protected]>
Co-authored-by: Yusuke Tsutsumi <[email protected]>

aep/general/0231/aep.md.j2

@@ -1,5 +1,179 @@
 # Batch methods: Get
 
-**Note:** This AEP has not yet been adopted. See
-[this GitHub issue](https://github.com/aep-dev/aep.dev/issues/42) for more
-information.
+Some APIs need to allow users to get a specific set of resources at a
+consistent time point (e.g. using a read transaction). A batch get method
+provides this functionality.
+
+## Guidance
+
+APIs **may** support batch get to retrieve a consistent set of resources.
+
+- The method's name **must** begin with `BatchGet`. The remainder of the method
+  name **must** be the plural form of the resource being retrieved.
+- The HTTP verb **must** be `GET`.
+- The HTTP URI **must** end with `:batchGet`.
+- The URI path **must** represent the collection for the resource, matching the
+  collection used for simple CRUD operations. If the operation spans parents, a
+  [wilcard](./reading-across-collections) **may** be accepted.
+- There **must not** be a request body.
+  - If a GET request contains a body, the body **must** be ignored, and **must
+    not** cause an error.
+
+### Request
+
+The request for a batch get method **should** be specified with the following
+pattern:
+
+- The request **must** include an array field which accepts the resource paths
+  specifying the resources to retrieve. The field **must** be named `paths`.
+  - If no resource paths are provided, the API **should** error with
+    `INVALID_ARGUMENT`.
+  - The parameter **must** be required.
+  - The documentation for the parameter **should** include the
+    [resource type](./paths) that it references.
+  - The parameter should define the pattern of the resource path values.
+  - The parameter should define the maximum number of paths allowed.
+- Batch Get **should not** support pagination because transactionality across
+  API calls would be extremely difficult to implement or enforce, and the
+  request defines the exact scope of the response anyway.
+- The request **must not** contain any other required parameters, and **should
+  not** contain other optional parameters except those described in this or
+  another AEP.
+
+{% tab proto -%}
+
+```proto
+rpc BatchGetBooks(BatchGetBooksRequest) returns (BatchGetBooksResponse) {
+  option (google.api.http) = {
+    get: "/v1/{parent=publishers/*}/books:batchGet"
+  };
+}
+
+message BatchGetBooksRequest {
+  // The parent resource shared by all books being retrieved.
+  // Format: publishers/{publisher}
+  // If this is set, the parent of all of the books specified in `paths`
+  // must match this field.
+  string parent = 1 [
+    (google.api.resource_reference) = {
+      child_type: "library.com/Book"
+    }];
+
+  // The paths of the books to retrieve.
+  // A maximum of 1000 books can be retrieved in a batch.
+  // Format: publishers/{publisher}/books/{book}
+  repeated string paths = 2 [
+    (google.api.field_behavior) = REQUIRED,
+    (google.api.resource_reference) = {
+      type: "library.com/Book"
+    }];
+}
+```
+
+- The request schema **must** match the method name, with `Request` suffix.
+- A `parent` field **should** be included, unless the resource being retrieved
+  is a top-level resource, to facilitate inclusion in the URI as well to permit
+  a single permissions check. If a caller sets this field, and the parent
+  collection in the path of any resource being retrieved does not match, the
+  request **must** fail.
+  - This field **should** be required if only 1 parent per request is allowed.
+  - The field **should** identify the [resource type][aep-122-parent] that it
+    references.
+  - The comment for the field **should** document the resource pattern.
+- There **must not** be a body key in the `google.api.http` annotation.
+
+{% tab oas %}
+
+{% sample 'batchget.oas.yaml', 'paths' %}
+
+- The `paths` parameter **must** be a query parameter which accepts an array of
+  resource paths specifying the resources to retrieve.
+  - If no resource paths are provided, the API **should** error with status
+    code `400 Bad Request`.
+  - If the collection in the path of any resource does not match the collection
+    of the request URL, the request **must** fail.
+- The method definition **must not** have a `requestBody` defined.
+
+{% endtabs %}
+
+### Response
+
+The response for a batch get method **must** be specified with the following
+pattern:
+
+- The response schema **must** match the method name, with `Response` suffix.
+- The response schema **must** have a single array property where each item is
+  either a retrieved resource or an error structure describing an error that
+  occurred attempting to retrieve the resource. The error alternative would
+  only be present for non-transactional batch gets.
+- The order of resources/error objects in the response **must** be the same as
+  the paths in the request.
+- The array of resources **must** be named `results` and contain resources with
+  no additional wrapping.
+- There **must not** be a `nextPageToken` field as batch get operations are not
+  pageable.
+
+{% tab proto -%}
+
+```proto
+message BatchGetBooksResponse {
+  // Books requested.
+  repeated Book books = 1;
+}
+```
+
+{% tab oas %}
+
+{% sample 'batchget.oas.yaml', '/publishers/{publisherId}/books:BatchGet' %}
+
+Example response body:
+
+```json
+{
+  "results": [
+    {
+      "name": "publishers/lacroix/books/les-mis",
+      "isbn": "978-037-540317-0",
+      "title": "Les Misérables",
+      "authors": ["Victor Hugo"],
+      "rating": 9.6
+    },
+    {
+      "type": "https://datatracker.ietf.org/doc/html/rfc9110#name-404-not-found",
+      "title": "The resource is not available"
+    }
+    {
+      "name": "publishers/lacroix/books/hunchback-of-notre-dame",
+      "isbn": "978-140-274575-1",
+      "title": "The Hunchback of Notre Dame",
+      "authors": ["Victor Hugo"],
+      "rating": 9.3
+    }
+  ]
+}
+```
+
+{% endtabs %}
+
+### Support for transactional get
+
+The batch get method may support a transactional form of operation where the
+get either succeeds for all requested resources or fails. When supported, the
+method must define a boolean parameter `transactional` that the user must
+specify with the value `true` to request a transactional operation.
+
+## Changelog
+
+- **2024-04-22:** Adopt from Google AIP https://google.aip.dev/231 with the
+  following changes:
+  - Dropped the "nested requests" pattern.
+  - Changed the response schema to an object with `results` array property.
+  - Made transactional operation optional and controlled by asTransaction
+    parameter.
+
+<!-- Links -->
+
+[aep-122-paths]: ./0122.md#fields-representing-resource-paths
+[aep-122-parent]: ./0122.md#fields-representing-a-resources-parent
+[aep-132]: https://aep.dev/132
+[get-request]: ./0131.md#get-request

aep/general/0231/aep.yaml

@@ -1,7 +1,7 @@
 ---
 id: 231
-state: reviewing
+state: approved
 slug: batch-get
-created: 2023-01-22
+created: 2024-04-22
 placement:
   category: batch-methods

aep/general/0231/batchget.oas.yaml

@@ -0,0 +1,71 @@
+openapi: 3.0.3
+info:
+  title: Library
+  version: 1.0.0
+paths:
+  /publishers/{publisherId}/books:BatchGet:
+    parameters:
+      - name: publisherId
+        in: path
+        required: true
+        schema:
+          type: string
+    get:
+      operationId: BatchGetBooks
+      description: Get multiple books in a batch.
+      parameters:
+        - name: paths
+          in: query
+          required: true
+          description: >-
+            The paths of the books to retrieve. Format:
+            publishers/{publisherId}/books/{book}
+          schema:
+            type: array
+            minItems: 1
+            maxItems: 1000
+            items:
+              type: string
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  results:
+                    type: array
+                    items:
+                      oneOf:
+                        - $ref: '#/components/schemas/Book'
+                        - $ref: '#/components/schemas/Error'
+components:
+  schemas:
+    Book:
+      description: A representation of a single book.
+      type: object
+      properties:
+        name:
+          type: string
+          description: |
+            The name of the book.
+            Format: publishers/{publisher}/books/{book}
+        isbn:
+          type: string
+          description: |
+            The ISBN (International Standard Book Number) for this book.
+        title:
+          type: string
+          description: The title of the book.
+        authors:
+          type: array
+          items:
+            type: string
+          description: The author or authors of the book.
+        rating:
+          type: number
+          format: float
+          description: The rating assigned to the book.
+    Error:
+      type: object