Imagine I have an angular project as a front-end which communicates with some other projects which are restful services.
In some pages I need to fetch some data from different restful services,
Is that okay to request any restful service individually in angular?
Or call one restful service which itself call other restful services in back-end?
Or I have to call one restful service but add other entities to this DbContext which I need here just to query?
It depends on what you're doing, but I would say mostly it's OK to do this. This is an established microservices pattern called "Composite UI". See this for details: https://learn.microsoft.com/en-us/dotnet/standard/microservices-architecture/architect-microservice-container-applications/microservice-based-composite-ui-shape-layout
If your microservices are using the CQRS pattern, (while still not wrong) you may be missing an opportunity to compose a view-specific "view model". However, if you're composing\showing data from multiple domains I would say that it's still better to just call multiple microservices to retrieve the data you need.
The only problem you may be introducing if you're not careful, is introducing projection logic (which is not THAT bad) or business logic (very very bad) in your client code if you're doing any processing on the data you receive in order to display it. Composite UI is meant to server a UI with clearly separated sections.
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I am building an ecommerce website for a project for my portfolio, and I wanted to know where the calculations should be done for the cart.
Normally I use react and I create a model folder, route folder and a controller folder but the way I was taught Angular it seems like the services acts like the routes and the actual calls to the database are done in the node server file which I am sure I could separate into a separate controller file. My question is where should the calculations for the cart be done before I send the order to the database? I thought about doing it in the cart component before the order is place or should it be done in the services or in the backend in the controller? I am just trying to figure out what is the standard
When writing an Angular app, I think it is important to adhere to the following principles that:
Components - should have a single responsibility for simple view logic only, shouldn't reach out to the server, and shouldn't do complex calculations and/or logic that is not related to the view.
Services - should have a single responsibility for (reusable/shared) and complex logic, to do outbound communication and reach out to the server, and to act as data stores (using BehaviorSubjects).
Therefore, if your calculations are needed to update the view of the cart, I would vote that these calculations need to be made at the component. If your calculations are needed to update the items or the request to be sent to the server, they need to be made at the service.
Remember, the component "shouldn't know" how the data comes to it or how it is manipulated or sent to the server. The component should only know, given any data - how to present it in the view, and shouldn't "worry about" how that data came to it. Similarly, the component shouldn't know how the data is calculated before being sent to the server, and this would fall within the responsibility of the service that works with and processes the cart data and builds the request to the server.
However, you have to always consider the security of your app, and if a malicious data modification at the client side can affect your cart. If such caculations affect the app's security - they should at least be validated at the server if not fully delegated to it.
I don't know the calculation you need exactly, but since it is an e-commerce website I assume it is simple math such as the total payment amount of checkout.
The main role of the server is communicating to the database. If a task does not involve interacting with data, you can do the calculations on the client-side. Leaving details on client-side allows you to have access to details of your formula, and reduce the communication time between client and server.
So i want to develop a simple web application, which will basically be a basic form which on submission will allow to make an external api request. So are there any application designers that can allow to do that with minimalistic code. Appian for example has an interface/application designer that lets you drag and drop a UI interface and build a workflow, make api calls externally or to a database. So like that are there any other apps that allow to do something similar (make api calls/build ui easily/store in databse)? Any other suggestions are also welcome!
It heavily depends on the API as well as the kind of task you´re trying to achieve.
Here´s just a few examples and considerations. (All the below supposes that we´re talking about Web-Based APIs).
If the API requires authentication of some sort and the user authenticates himself: A simple HTTP file with JavaScript to send the request will do the job
If the API requires authentication but you authenticate for all the users: You will need a backend application that does the API request since you need something secure where you can put your Auth-Details for the API. Classic PHP or NodeJS in combination with a served HTTP file for the form itself would work without any JavaScript (depends on the API definitions)
If the API does not require authentication maybe a simple HTML form would work
If you want to write to a database you can have a look at something like https://directus.io/. They allow building a database with a UI and they automatically generate a Web-API which you can then feed by your forms. If the end-user is known to you Directus actually allows users to log in and fill the database with forms that you can visually design but this is rather for employees entering data into an internal database than customers submitting their contact data to you
From my personal experience, all the UI-Tools that promise to integrate with REST APIs make it really hard to do so since every API is different and there is no real standard for them.
To start: I've tried Loopback. Loopback is nice but does not allow for relations across multiple REST data services, but rather makes a call to the initial data service and passes query parameters that ask it to perform the joined query.
Before I go reinventing the wheel and writing a massive wrapper around Loopback's loopback-rest-connector, I need to find out if there are any existing libraries or frameworks that already tackle this. My extensive Googling has turned up nothing so far.
In a true microservice environment, there is a service per database.
http://microservices.io/patterns/data/database-per-service.html
From this article:
Implementing queries that join data that is now in multiple databases
is challenging. There are various solutions:
Application-side joins - the application performs the join rather than
the database. For example, a service (or the API gateway) could
retrieve a customer and their orders by first retrieving the customer
from the customer service and then querying the order service to
return the customer’s most recent orders.
Command Query Responsibility Segregation (CQRS) - maintain one or more
materialized views that contain data from multiple services. The views
are kept by services that subscribe to events that each services
publishes when it updates its data. For example, the online store
could implement a query that finds customers in a particular region
and their recent orders by maintaining a view that joins customers and
orders. The view is updated by a service that subscribes to customer
and order events.
EXAMPLE:
I have 2 data microservices:
GET /pets - Returns an object like
{
"name":"ugly",
"type":"dog",
"owner":"chris"
}
and on a completely different microservice....
GET /owners/{OWNER_NAME} - Returns the owner info
{
"owner":"chris",
"address":"under a bridge",
"phone":"123-456-7890"
}
And I have an API-level microservice that is going to call these two data services. This is the microservice that I will be applying this at.
I'd like to be able to establish a model for Pet such that, when I query pet, upon a successful response from GET /pets, it will "join" with owners (send a GET /owners/{OWNERS_NAME} for all responses), and to the user, simply return a list of pets that includes their owner's data.
So GET /pets (maybe something like Pets.find()) would return
{
"name":"ugly",
"type":"dog",
"owner": "chris",
"address": "under a bridge",
"phone": "123-456-7890"
}
Applying any model/domain logic on your API-gateway is bad decision, and considered as bad practice. API Gateway should only do your systems's CAS (with relying onto Auth service which holds the logic), And convert incoming external requests into inner system requests (different headers/ requester payload data) and proxy formatted requests to services for any other work, recieves them, cares about encapsulating errors, and presents every response in proper external form.
Another point, if there is alot of joins between two models required for application core flow (validation/scoping etc) then perhaps you should reconsider to which Business Domain your models/services are bound. If it's same BD perhaps they should be together. Priciples of Domain-Driven-Design helped me to understand where real boundaries between micro-services are.
If you work with loopback (like we are and face same problem we faced - that loopback have no proper join implementation) you can have separate Report/Combined data service, which is only one who can access to all the service databases and does it only for READ purposes - i.e. queries. Provide it with separately set-up read-only wide access to the db - instead of having only one datasource being set up (single database) it should be able to read from all the databases which are in scope of this query-join db user.
Such service should able to generate proper joins with expected output schema from configuration json - like loopback models (thats what I did in same case). Once abstraction is done it's pretty simple to build/add any equery with any complex joins. It's clean, and it's easy to reason about. Also, it's DBA friendly. For me such approach worked well so far.
I am developing a Nodejs application and my database is Postgres and I am using Sequelize as my ORM because of its excellent support for migrations.
I am on the lookout for a good REST API generator based on the schema I have defined. There are two main hurdles I am facing and they are that the generators don't do a good job of creating association API routes and lack of ACL support.
On the associations front, my schema has multiple levels of association i.e. for example..
Student.hasMany(Courses);
Courses.hasMany(Subjects);
So ideally the generated REST API should be something like
/student/:student_id/course/:course_id/subject/:subjectId
I found a few projects that are doing this, but are incomplete.
https://github.com/sequelize/sequelize-restful - is good but does not have ACL support
https://www.npmjs.org/package/restizr - is in alpha stage and does not generate API routes for associations.
Is there any module that supports this?
What you were doing here is writing a webservice without a domain model. https://en.wikipedia.org/wiki/Anemic_domain_model Ofc. you have every right to do it, but I wonder if you really understood what a webservice means. https://stackoverflow.com/a/1530607/607033 It is not a database with CRUD HTTP interface normally, though nowadays it is popular doing something this way and call it REST. A response to a REST HTTP request is a viewmodel https://softwareengineering.stackexchange.com/a/425001/65755 and it contains not just data, but a lot of metadata and hyperlinks. A REST API is a special type of webservice with many constraints. https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation.pdf http://www.markus-lanthaler.com/research/hydra-a-vocabulary-for-hypermedia-driven-web-apis.pdf Your ORM is used 2 layers deeper in the data layer and it has nothing to do with the presentation layer where your REST API should be. I really wonder why people are making applications, which are doing nothing except serving data directly from the database and use the most inconvenient technology to do it. I guess there are databases nowadays with ACL and REST API support, so all you need is just using them. https://learn.microsoft.com/en-us/rest/api/sql/ Or there was something for PgSQL and Nodejs too around the time you asked this. https://github.com/QBisConsult/psql-api
(I'm not familiar to RESTFul, please correct me if my concept is wrong)
In RESTFul architecture, we map every action to an URL. If I click "post a article", may it's actually URL http://example.com/ and some data action=post&content=blahblah.
If I want to post, but not refresh the whole web page, I can use javascript's XMLHTTPRequest. I post it and then get it's content and insert it to a div in my page. These action is all asynchronous.
Then I know there is something named WebSocket and it's wrapper socket.io. It use "message" to communicate between client and server. When I click "post" the client just call socket.send(data) and wait for server's client.send(data). It's magical. But how about URL?
It's possible to use the two model both without repeating myself? In other word, every action has it's URL, and some of them can interact with user real-timely(by socket.io?)
Moreover, should I do this? In a very interactive web program(ex. games), the RESTFul is still meaningful?
You're defining a handler for actions that map to REST over http. POST and GET generally refer to update and query over an entity. There's absolutely no reason you can't just define a handler for generic versions of these CRUD operations that can be used in both contexts. The way I generally do this is by introducing the concept of a 'route' to the real-time transport, and mapping those back to the same CRUD handlers.
You have a session, you can impose the same ACL, etc.
+---------------------------------+
| |
| BROWSER |
| |
+--+--^-------------------+---^---+
| | | |
| | | |
+--v--+---+ +--v---+---+
| | | |
| HTTP | | SOCKET.IO|
+--+---^--+ +--+---^---+
| | | |
+--v---+------------------v---+---+
| |
| ROUTING/PUBSUB |
+-+--^-------+--^-------+--^------+
| | | | | |
+-v--+--+ +-v--+--+ +-v--+-+
| | | | | |
| USERS | | ITEMS | |ETC |
+-------+ +-------+ +------+
ENTITY CRUD HANDLERS
I posted this on my blog recently:
Designing a CRUD API for WebSockets
When building Weld, we are using both REST and WebSockets (Socket.io). Three observations on WebSockets:
Since WebSockets are so free-form, you can name events how you want but it will eventually be impossible to debug.
WebSockets don’t have the request/response form of HTTP so sometimes it can be difficult to tell where an event is coming from, or going to.
It would be nice if the WebSockets could fit into the existing MVC structure in the app, preferably using the same controllers as the REST API.
My solution:
I have two routing files on my server: routes-rest.js and routes-sockets.js
My events look like this example: "AppServer/user/create".
I use forward slashes (“/”) to make the events look like routing paths.
The first string is the target (~”host name” if this actually was a path).
The second string is the model.
The third string is the CRUD verb: i.e. create, read, update, delete.