Google Cloud Endpoints API的DRY代码

Question

我希望避免使用样板代码为我的Google App Engine应用程序的不同模型创建Google Cloud Endpoints App。假设我有一个Post、User和Category模型。数据存储在数据存储区中。我想使用资源posts、users和categories创建REST API。我为posts资源编写了以下代码：

import endpoints
from protorpc import messages
from protorpc import message_types
from protorpc import remote
from blog.models import Post
from cloud_endpoints import WEB_CLIENT_ID, ANDROID_CLIENT_ID, IOS_CLIENT_ID, ANDROID_AUDIENCE


class PostMessage(messages.Message):
    id = messages.StringField(1)
    title = messages.StringField(2)
    body = messages.StringField(3)


class PostMessageCollection(messages.Message):
    post_messages = messages.MessageField(PostMessage, 1, repeated=True)


def post_to_message(post):
    return PostMessage(
        id=str(post.key()),
        title=post.title,
        body=post.body)


ID_RESOURCE = endpoints.ResourceContainer(
    message_types.VoidMessage,
    id=messages.StringField(1, variant=messages.Variant.STRING))

PUT_RESOURCE = endpoints.ResourceContainer(
    PostMessage,
    id=messages.StringField(1, variant=messages.Variant.STRING))

POST_RESOURCE = endpoints.ResourceContainer(Post)


@endpoints.api(name='posts',
               version='v1',
               allowed_client_ids=[WEB_CLIENT_ID, ANDROID_CLIENT_ID, IOS_CLIENT_ID],
               audiences=[ANDROID_AUDIENCE])
class PostsApi(remote.Service):
    """List"""
    @endpoints.method(message_types.VoidMessage,
                      PostMessageCollection,
                      path='/posts',
                      http_method='GET',
                      name='posts.listPosts')
    def list(self, unused_request):
        post_messages = []
        for post in Post.all():
            post_messages.append(post_to_message(post))

        return PostCollection(post_messages=post_messages)

    """Get"""
    @endpoints.method(ID_RESOURCE,
                      PostMessage,
                      path='/posts/{id}',
                      http_method='GET',
                      name='posts.getPost')
    def get(self, request):
        try:
            return post_to_message(Post.get(request.id))

        except (IndexError, TypeError):
            raise endpoints.NotFoundException('Post %s not found.' % (request.id,))

    """Create"""
    @endpoints.method(POST_RESOURCE,
                      message_types.VoidMessage,
                      path='/posts',
                      http_method='POST',
                      name='posts.createPost')
    def create(self, request):
        post = Post(title=request.title, body=request.body)\
        post.put()
        return message_types.VoidMessage()

    """Update"""
    @endpoints.method(PUT_RESOURCE,
                      message_types.VoidMessage,
                      path='/posts/{id}',
                      http_method='POST',
                      name='posts.updatePost')
    def update(self, request):
        try:
            post = Post.get(request.id)
            post.title = request.title
            post.body = request.body
            return message_types.VoidMessage()
        except (IndexError, TypeError):
            raise endpoints.NotFoundException('Post %s not found.' % (request.id,))

    """Delete"""
    @endpoints.method(ID_RESOURCE,
                      message_types.VoidMessage,
                      path='/posts/{id}',
                      http_method='DELETE',
                      name='posts.deletePost')
    def delete(self, request):
        try:
            post = Post.get(request.id)
            post.delete()
            return message_types.VoidMessage()

        except (IndexError, TypeError):
            raise endpoints.NotFoundException('Post %s not found.' % (request.id,))

我可以复制/粘贴这段代码，将“发布”更改为“分类”，还可以编辑PostMessage、PostMessageCollection和post_to_message，但这似乎不是什么好做法。我不想重复我的话。可以创建一个抽象API类并为PostAPI、CategoryAPI和UserAPI创建子类吗？或者，有没有更好的方法来参数化Post、PostMessage、PostMessageCollection、post_to_message和资源的路径("/posts“、"/categories”和"/users")，这样我就不必复制/粘贴每个资源的类了？这些类将具有相同的方法和相同的装饰器，我不想为每个资源重复这一点。我使用的是Python 2.7。

Answer 1

我也偶然发现了同样的问题，不幸的是，这在google cloud endpoints上是不可能的。方法装饰器需要请求描述(这里是PostMessageCollection)。对message.Message进行子类化的请求描述不允许通过继承进行重用，因此所有消息类都必须在没有任何继承的情况下完全定义。

但是，您可以通过以下方式在某种程度上实现这一点(尽管我还没有测试过它，现在就想到了:)：

# All the message and response definitions have to be here, complete.

class PostMessage(messages.Message):
    id = messages.StringField(1)
    title = messages.StringField(2)
    body = messages.StringField(3)


class PostMessageCollection(messages.Message):
    post_messages = messages.MessageField(PostMessage, 1, repeated=True)


def post_to_message(post):
    return PostMessage(
        id=str(post.key()),
        title=post.title,
        body=post.body)


ID_RESOURCE = endpoints.ResourceContainer(
    message_types.VoidMessage,
    id=messages.StringField(1, variant=messages.Variant.STRING))

PUT_RESOURCE = endpoints.ResourceContainer(
    PostMessage,
    id=messages.StringField(1, variant=messages.Variant.STRING))

POST_RESOURCE = endpoints.ResourceContainer(Post)

# Now define all the 'Category' related messages here.


@endpoints.api(name='posts_n_categories',  # The name can be a common one.
               version='v1',
               allowed_client_ids=[WEB_CLIENT_ID, ANDROID_CLIENT_ID, IOS_CLIENT_ID],
               audiences=[ANDROID_AUDIENCE])
class BaseAPI(remote.Service):
    """List"""
    # Common defs go here.
    MessageCollection = messages.Message
    PATH = '/'
    NAME = ''

    @staticmethod
    def converter(x):
        raise NotImplemented

    iterator = []
    collection = messages.Message
    @endpoints.method(message_types.VoidMessage,
                      MessageCollection,
                      path=PATH,
                      http_method='GET',
                      name=NAME)
    def list(self, unused_request):
        # Do the common work here. You can 
        _messages = []
        for post in self.__class__.iterator.all():
            _messages.append(self.__class__.converter(post))

        return self.__class__.collection(post_messages=_messages)




@endpoints.api(name='posts',  # The name can be different.
               version='v1',
               allowed_client_ids=[WEB_CLIENT_ID, ANDROID_CLIENT_ID, IOS_CLIENT_ID],
               audiences=[ANDROID_AUDIENCE])
class PostAPI(Base):
    # Post specific defs go here.
    MessageCollection = PostMessageCollection
    PATH = '/posts'
    NAME = 'posts.listPosts'
    converter = post_to_message
    iterator = Post
    collection = PostCollection


# Define the category class here.

显然，这并不能节省太多时间。

Answer 2

这个帖子已经有两年的历史了，但无论如何我都会提出一个想法。它有一个明显的缺陷；下面有更多关于这方面的内容。

我将假设您正在通过ndb API使用数据存储。

其想法是引入通用消息类(EntityContainer，EntityContainerList)，这些类可以包含任何特定于应用程序的消息类的实例，并包括一个将路由映射到protorpc和ndb类的字典：

model.py

class Book(ndb.Model):
    title = ndb.StringProperty()
    author = ndb.StringProperty()

class Movie(ndb.Model):
    title = ndb.StringProperty()
    director = ndb.StringProperty()

main.py

class Book(messages.Message):
    title = messages.StringField(1)
    author = messages.StringField(2)

class Movie(messages.Message):
    title = messages.StringField(1)
    director = messages.StringField(2)

class EntityContainer(messages.Message):
    book = messages.MessageField(Book, 1)
    movie = messages.MessageField(Movie, 2)
    id_ = messages.StringField(3)

class EntityContainerList(messages.Message):
    entities = messages.MessageField(EntityContainer, 1, repeated=True)

Map = {
    'books': {
        'message_class': Book,
        'ndb_model_class': model.Book,
        'entity_container_key': 'book'
    },
    'movies': {
        'message_class': Movie,
        'ndb_model_class': model.Movie,
        'entity_container_key': 'movie'
    }
}

@endpoints.api(name='testApi', version='v1')
class TestApi(remote.Service):

    GET_RESOURCE = endpoints.ResourceContainer(
        id_=messages.StringField(1),
        entities=messages.StringField(2)
    )

    LIST_RESOURCE = endpoints.ResourceContainer(
        entities=messages.StringField(2)
    )   

    POST_RESOURCE = endpoints.ResourceContainer(
        EntityContainer,
        entities=messages.StringField(1),
    )

    @endpoints.method(
        GET_RESOURCE,
        EntityContainer,
        path='{entities}/{id_}',
        http_method="GET")
    def get_entity(self, request):
        # The path tells us what kind of entity we're fetching.
        Entity = Map[request.entities]['message_class']
        key = Map[request.entities]['entity_container_key']

        # Pull from database.
        ndb_entity = ndb.Key(urlsafe=request.id_).get()

        # Formulate response.
        entity_container = EntityContainer(**{key: Entity(**ndb_entity.to_dict())})
        entity_container.id_ = request.id_
        logging.info("\n\nResponse: %s\n" % str(entity_container))
        return entity_container

    @endpoints.method(
        LIST_RESOURCE,
        EntityContainerList,
        path='{entities}',
        http_method="GET")
    def list_entities(self, request):
        # The path tells us what kinds of entities we're fetching.
        Entity = Map[request.entities]['message_class']
        NdbModel = Map[request.entities]['ndb_model_class']
        key = Map[request.entities]['entity_container_key']

        # Pull from database
        query = NdbModel.query()

        # Formulate response.
        entities = [
            EntityContainer(**{'id_': q.key.urlsafe(), key: Entity(**q.to_dict())})
                for q in query
        ]
        entity_container_list = EntityContainerList(entities=entities)
        logging.info("\n\nEntity list: %s\n" % str(entity_container_list))
        return entity_container_list

    @endpoints.method(
        POST_RESOURCE,
        EntityContainer,
        path='{entities}',
        http_method='POST'
        )
    def post_entity(self, request):
        # The path tells us what kind of entity we're' creating.
        Entity = Map[request.entities]['message_class']
        NdbModel = Map[request.entities]['ndb_model_class']
        key = Map[request.entities]['entity_container_key']

        # Extract the body of the request
        body_message = getattr(request, key)
        body_dict = {f.name: getattr(body_message, f.name)
            for f in body_message.all_fields()
                if getattr(body_message, f.name)}

        # Write to database
        ndb_entity = NdbModel(**body_dict)
        ndb_key = ndb_entity.put()
        id_ = ndb_key.urlsafe()

        # Reload entity. Maybe some model hooks treated the data.
        ndb_entity = ndb_key.get()

        entity_container = EntityContainer(**{key: Entity(**ndb_entity.to_dict())})
        entity_container.id_ = id_
        logging.info("\n\nResponse: %s\n" % str(entity_container))
        return entity_container

当然，您也可以使用DELETE、PUT和PATCH方法。

您拥有的消息类越多，这种方法可以节省的代码就越多。(我刚刚包含了两个-- Book和Movie --用于演示。)

上面提到的缺陷是EntityContainer类膨胀了消息字段，任何类实例都只使用其中的两个字段。我不知道事情是如何在引擎盖下工作的，所以我不能评估这件事的严重性。