I'm implementing a service that needs to call another service that calculates a result in a way I cannot know.
Let's say I have the following scenario:
I have some place in my code, calling a HTTP request to a defined endpoint another service returning a defined result. Now, I mustn't dictate how the result will be calculated, however I can define the result output data type I'm expecting. I want to put emphasis on this, since otherwise I would just implement the calculation logic in my service.
I would then describe it to the user:
You need to provide an HTTP service, with this exact endpoint, receiving these exact parameters, delivering this exact result type, but how you calculate the result is your job. I just need the URL of your service.
Afterwards the user of my service would configure the URL to their HTTP service into my service, so that I can make a HTTP request to {url}/defined-endpoint.
I couldn't think of another name but "service-injection" to describe this concept, since it has a resemblance to dependency injection, just that in code you don't provide an object instance, but a service that is called via http.
My question is: Is there a pattern for this concept or an alternative that more elegantly solves the general problem of outsourcing a calculation to another service?
You are defining a contract of how the interface between your service and the other service. This means that as long as the contract is respected by both parties the integration and communication will succeed. Not sure if "service-injection" is a good terminology for this. You are not injecting something in your own service, you are simply delegating the calculation to another one, but you don't inject the logic of the service into your own. And that is good because then you have a good separation of concerns and loose coupling. As long as the contract is respected, both services can be changed in whatever way it is needed and the integration would still hold.
Is there a pattern for this concept or an alternative that more elegantly solves the general problem of outsourcing a calculation to another service?
This is just how things work in a micro-services ecosystem. You have multiple services exposing APIs that communicate with each other to provide as a whole a higher-order functionality.
I need the exact purpose of Service layer in MVC.
Can we implement without service layer..
What are the major responsibilities of these layers..
Can we implement without anyone of these layers..
Can you please someone help me to know this..
The service layer is there to provide logic to operate on the data sent to and from the DAO and the client. Very often these 2 pieces will be bundled together into the same module, and occasionally into the same code, but you'll still see them as distinct logical entities.
This may helpful to you
https://softwareengineering.stackexchange.com/questions/220909/service-layer-vs-dao-why-both
DAO is as light and exists solely to provide a connection to the DB, sometimes abstracted so different DB backends can be used.
The service layer is there to provide logic to operate on the data sent to and from the DAO and the client. Very often these 2 pieces will be bundled together into the same module, and occasionally into the same code, but you'll still see them as distinct logical entities.
Yes you can implement without service layer but will lack the security.. and without using service layer the request and response works faster...
Another reason for Service layer is security - If you provide a service layer that has no relation to the DB, then is it more difficult to gain access to the DB from the client except through the service. If the DB cannot be accessed directly from the client (and there is no trivial DAO module acting as the service) then all an attacker who has taken over the client can do is attempt to hack the service layer as well before he gets all but the most sanitised access to your data.
As these answer is already answered on StackExchange.. by gbjbaanb
Background
I've been killing some neurons lately with this. I would like to make a multi-tier application for parcel services like UPS and such. Long story short, the backend will be a WCF-based server while the consumer will be an ASP.NET MVC application. The idea is that the backend will handle all business operations (like adding a new shipment, editing existing shipments, carriers and such) but will provide the consumer with data in form or queries.
And the Issue Is...?
My plan for business operations is that the consumer should pass all the information required to complete the operation (pretty much like a model, i.e. for adding shipments, the consumer would send all the required information for those shipments.) Now, my actual issue is with data querying.
The consumer application should be able to display the backend-provided data in anyway it desires, not limited by a DTO. For example, when listing shipments, I only want to show a grid with Name, ID, date shipped and such, not the entire shipment object graph.
How can the consumer application specify the data projection it needs to the WCF endpoint?
Options
I thought on creating several operation method overloads exposing different DTOs for different purposes. I.e.:
IList<ShipmentDetailsDTO> GetAllShipmentsAsDetailed();
IList<ShipmentListingItemDTO> GetAllShipmentsAsListingItems();
I dropped the idea since the backend is adapting to the consumer application needs, and this is not a good practice. The backend should be agnostic of the consumer.
Another option is to combine WCF data services for querying data and WCF regular services for business operations. This way the MVC application can project the data like a regular LINQ query against the WCF data services. Sounds quite elegant but I would like to hear a second opinion.
Any thoughts? What would you do if you were me? I need an elegant and practical solution for this.
I'm very new at WCF (and .NET in general), so I apologize if this is common knowledge.
I'm designing a WCF solution (currently using Entity Framework to access the database). I want to grab a (possibly very large) set of data from the database, and return it to the client, but I don't want to serialize the entire set of data over the wire all at once, due to performance concerns.
I'd like to operation to return some sort of object to the client that represents the resulting data and I'd like to deal with that data on the client, being able to navigate through it backwards and forwards and retrieve the actual data over the wire as needed.
I don't want to write a lot client code to individually find out what rows meet my search criteria, then make separate calls to get each record if I can help it. I'm trying to keep the client as simple as possible.
Ideally, I'd like to write the client code similar to something like the below pseudocode:
Reference1.Service1Client MyService = new Reference1.Service1Client("Service1");
DelayedDataSet<MyRecordType> MyResultSet = MyService.GetAllCustomers();
MyResultSet.First();
while (!MyResultSet.Eof)
{
Console.Writeline(MyResultSet.CurrentRecord().CUSTFNAME + " " + MyResultSet.CurrentRecord().CUSTLNAME);
Console.Writeline("Press Enter to see the next customer");
Console.Readline();
MyResultSet.Next();
}
Of course, DelayedDataSet is something I just made up, and I'm hoping something like it exists in .NET.
The call to MyService.GetAllCustomers() would return this DelayedDataSet object, with would not actually contain the actual records. The actual data wouldn't come over the wire until CurrentRecord() is called. Next() and Previous() would simply update a cursor on the server side to point to the appropriate record. I don't want the client to have any direct visibility to the database or Entity Framework.
I'm guessing that the way I wrote the code probably won't work over WCF, and that the functions like CurrentRecord(), Next(), First(), etc. would have to be separate service contract operations. I guess I'm just looking for a way to do this without having to write all my own code to cache the results on the server, somehow persist the data sets server side, write all the retrieval and navigation code in my service library, etc. I'm hoping most of this is already done for me.
It seems like this would be a very commonly needed function. So, does something like this exist?
-Joe
No, that's not what WCF is designed to do.
In WCF, the very basic core architecture is that you have a client and a server, and nothing but (XML-)serialized data going between the two over the wire.
WCF is not a remote-procedure call method, or some sort of remote object mechanism - there is no connection between the client and the server except the serialized message that conforms to the service (and data) contracts defined between the two.
WCF is not designed to handle huge data volumes - it's designed to handle individual messages (GetCustomerByID(42) and such). Since WCF is from the ground up designed to be interoperable with other platforms (non - .NET, too - like Java, Ruby etc.) you should definitely not be using heavy-weight .NET specific types like DataSet anyway - use proper objects.
Also, since WCF ultimately serializes everything to XML and send it across a wire, all the data being passed must be expressible in XML schema - which excludes interfaces and/or generics.
From what I'm reading in your post, what you're looking for is more of a "in-proc" data access layer - not a service level. So if you want to keep going down this path, you should investigate the repository and unit-of-work patterns in conjunction with Entity Framework.
More info:
MSDN: What is Windows Communication Foundation?
WCF Essentials—A Developer's Primer
Picture of the very basic WCF architecture from that Primer - there's only a wire with a serialized message connecting client and server - nothing more; but serialization will always happen
After reading a lot about the differences between REST and SOAP, I got the impression that REST is just another word for HTTP. Can someone explain what functionality REST adds to HTTP?
Note: I'm not looking for a comparison of REST versus SOAP.
No, REST is the way HTTP should be used.
Today we only use a tiny bit of the HTTP protocol's methods – namely GET and POST. The REST way to do it is to use all of the protocol's methods.
For example, REST dictates the usage of DELETE to erase a document (be it a file, state, etc.) behind a URI, whereas, with HTTP, you would misuse a GET or POST query like ...product/?delete_id=22.
HTTP is a protocol used for communication, usually used to communicate with internet resources or any application with a web browser client.
REST means that the main concept you are using while designing the application is the Resource: for each action you want to perform you need to define a resource on which you often do only CRUD operation, which is a simple task. For that it's very convenient to use four verbs used in HTTP protocol against the four CRUD operations (GET for Read, POST is for CREATE, PUT is for UPDATE and DELETE is for DELETE).
That's unlike the older concept of RPC (Remote Procedure Call), in which you have a set of actions you want to perform as a result of the user's call. if you think for example on how to describe a Facebook like on a post, with RPC you might create services called AddLikeToPost and RemoveLikeFromPost, and manage it along with all your other services related to FB posts, thus you won't need to create special object for Like.
With REST you will have a Like object which will be managed separately with Delete and Create functions. It also means it will describe a separate entity in your DB. That might look like a small difference, but working like that would usually yield a much simpler code and a much simpler application. With that design, most of the app's logic is obvious from the object's structure (model), unlike RPC with which you would usually have to explicitly add a lot more logic.
Designing a RESTful application is often a lot harder because it requires you to describe complicated things in a simple manner. Describing all functionalities using only CRUD functions is tricky, but after doing that your life would be a lot simpler, and you will find that you write a lot shorter methods.
One more restraint REST architecture presents is not to use a session context when communicating with a client (stateless), meaning all the information needed to understand who is the client and what he wants is passed with the web message. Each call to a function is self-descriptive, there is no previous conversation with the client which can be referenced in the message. Therefore, a client could not tell you "give me the next page" since you don't have a session to store what is the previous page and what kind of page you want, the client would have to say "my name is Yuval, get me page 2 of a specific post in a specific forum". This means a bit more data would have to transfer in the communication, but think of the difference between finding a bug reported from the "get me the next page" function in oppose to "get me page 2 of question ID 2190836 in stack overflow".
Of course there is a lot more to it, but to my humble opinion these are the main concepts in a teaspoon.
REST enforces the use of the available HTTP commands as they were meant to be used.
For example, I could do:
GET
http://example.com?method=delete&item=xxx
But with rest I would use the "DELETE" request method, removing the need for the "method" query param
DELETE
http://example.com?item=xxx
HTTP is an application protocol. REST is a set of rules, that when followed, enable you to build a distributed application that has a specific set of desirable constraints.
If you are looking for the most significant constraints of REST that distinguish a RESTful application from just any HTTP application, I would say the "self-description" constraint and the hypermedia constraint (aka Hypermedia as the Engine of Application State (HATEOAS)) are the most important.
The self-description constraint requires a RESTful request to be completely self descriptive in the users intent. This allows intermediaries (proxies and caches) to act on the message safely.
The HATEOAS constraint is about turning your application into a web of links where the client's current state is based on its place in that web. It is a tricky concept and requires more time to explain than I have right now.
HTTP is a contract, a communication protocol and REST is a concept, an architectural style which may use HTTP, FTP or other communication protocols but is widely used with HTTP.
REST implies a series of constraints about how Server and Client should interact. HTTP is a communication protocol with a given mechanism for server-client data transfer, it's most commonly used in REST API just because REST was inspired by WWW (world wide web) which largely used HTTP before REST was defined, so it's easier to implement REST API style with HTTP.
There are three major constraints in REST (but there are more):
Interaction between server and client should be described via hypertext only.
Server and client should be loosely coupled and make no assumptions about each other. Client should only know resource entry point. Interaction data should be provided by the server in the response.
Server shouldn't store any information about request context. Requests must be independent and idempotent (means if same request is repeated infinitely, exactly same result is retrieved)
And HTTP is just a communication protocol (a tool) that can help to achieve this.
For more info check these links:
https://martinfowler.com/articles/richardsonMaturityModel.html
http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hypertext-driven
REST = Representational State Transfer
REST is a set of rules, that when followed, enable you to build a distributed application that has a specific set of desirable constraints.
REST is a protocol to exchange any(XML, JSON etc ) messages that can use HTTP to transport those messages.
Features:
It is stateless which means that ideally no connection should be maintained between the client and server.
It is the responsibility of the client to pass its context to the server and then the server can store this context to process the client's further request. For example, session maintained by server is identified by session identifier passed by the client.
Advantages of Statelessness:
Web Services can treat each method calls separately.
Web Services need not maintain the client's previous interaction.
This in turn simplifies application design.
HTTP is itself a stateless protocol unlike TCP and thus RESTful Web Services work seamlessly with the HTTP protocols.
Disadvantages of Statelessness:
One extra layer in the form of heading needs to be added to every request to preserve the client's state.
For security we need to add a header info to every request.
HTTP Methods supported by REST:
GET: /string/someotherstring
It is idempotent and should ideally return the same results every time a call is made
PUT:
Same like GET. Idempotent and is used to update resources.
POST: should contain a url and body
Used for creating resources. Multiple calls should ideally return different results and should create multiple products.
DELETE:
Used to delete resources on the server.
HEAD:
The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The meta information contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request.
OPTIONS:
This method allows the client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
HTTP Responses
Go here for all the responses.
Here are a few important ones:
200 - OK
3XX - Additional information needed from the client and url redirection
400 - Bad request
401 - Unauthorized to access
403 - Forbidden
The request was valid, but the server is refusing action. The user might not have the necessary permissions for a resource, or may need an account of some sort.
404 - Not Found
The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.
405 - Method Not Allowed
A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.
404 - Request not found
500 - Internal Server Failure
502 - Bad Gateway Error
Not quite...
http://en.wikipedia.org/wiki/Representational_State_Transfer
REST was initially described in the
context of HTTP, but is not limited to
that protocol. RESTful architectures
can be based on other Application
Layer protocols if they already
provide a rich and uniform vocabulary
for applications based on the transfer
of meaningful representational state.
RESTful applications maximise the use
of the pre-existing, well-defined
interface and other built-in
capabilities provided by the chosen
network protocol, and minimise the
addition of new application-specific
features on top of it.
http://www.looselycoupled.com/glossary/SOAP
(Simple Object Access Protocol) The
standard for web services messages.
Based on XML, SOAP defines an envelope
format and various rules for
describing its contents. Seen (with
WSDL and UDDI) as one of the three
foundation standards of web services,
it is the preferred protocol for
exchanging web services, but by no
means the only one; proponents of REST
say that it adds unnecessary
complexity.
REST is a specific way of approaching the design of big systems (like the web).
It's a set of 'rules' (or 'constraints').
HTTP is a protocol that tries to obey those rules.
From You don't know the difference between HTTP and REST
So REST architecture and HTTP 1.1 protocol are independent from each
other, but the HTTP 1.1 protocol was built to be the ideal protocol to
follow the principles and constraints of REST. One way to look at the
relationship between HTTP and REST is, that REST is the design, and
HTTP 1.1 is an implementation of that design.
HTTP is a communications protocol that transports messages over a network.
SOAP is a protocol to exchange XML-based messages that can use HTTP to transport those messages.
Rest is a protocol to exchange any(XML or JSON) messages that can use HTTP to transport those messages.
REST is not necessarily tied to HTTP. RESTful web services are just web services that follow a RESTful architecture.
What is Rest -
1- Client-server
2- Stateless
3- Cacheable
4- Layered system
5- Code on demand
6- Uniform interface
REST APIs must be hypertext-driven
From Roy Fielding's blog here's a set of ways to check if you're building a HTTP API or a REST API:
API designers, please note the following rules before calling your creation a REST API:
A REST API should not be dependent on any single communication protocol, though its successful mapping to a given protocol may be dependent on the availability of metadata, choice of methods, etc. In general, any protocol element that uses a URI for identification must allow any URI scheme to be used for the sake of that identification. [Failure here implies that identification is not separated from interaction.]
A REST API should not contain any changes to the communication protocols aside from filling-out or fixing the details of underspecified bits of standard protocols, such as HTTP’s PATCH method or Link header field. Workarounds for broken implementations (such as those browsers stupid enough to believe that HTML defines HTTP’s method set) should be defined separately, or at least in appendices, with an expectation that the workaround will eventually be obsolete. [Failure here implies that the resource interfaces are object-specific, not generic.]
A REST API should spend almost all of its descriptive effort in defining the media type(s) used for representing resources and driving application state, or in defining extended relation names and/or hypertext-enabled mark-up for existing standard media types. Any effort spent describing what methods to use on what URIs of interest should be entirely defined within the scope of the processing rules for a media type (and, in most cases, already defined by existing media types). [Failure here implies that out-of-band information is driving interaction instead of hypertext.]
A REST API must not define fixed resource names or hierarchies (an obvious coupling of client and server). Servers must have the freedom to control their own namespace. Instead, allow servers to instruct clients on how to construct appropriate URIs, such as is done in HTML forms and URI templates, by defining those instructions within media types and link relations. [Failure here implies that clients are assuming a resource structure due to out-of band information, such as a domain-specific standard, which is the data-oriented equivalent to RPC’s functional coupling].
A REST API should never have “typed” resources that are significant to the client. Specification authors may use resource types for describing server implementation behind the interface, but those types must be irrelevant and invisible to the client. The only types that are significant to a client are the current representation’s media type and standardized relation names. [ditto]
A REST API should be entered with no prior knowledge beyond the initial URI (bookmark) and set of standardized media types that are appropriate for the intended audience (i.e., expected to be understood by any client that might use the API). From that point on, all application state transitions must be driven by client selection of server-provided choices that are present in the received representations or implied by the user’s manipulation of those representations. The transitions may be determined (or limited by) the client’s knowledge of media types and resource communication mechanisms, both of which may be improved on-the-fly (e.g., code-on-demand). [Failure here implies that out-of-band information is driving interaction instead of hypertext.]
REST is a light version of SOAP, with no sugars or colors agents added.
The goal of both SOAP and REST is to allow the communication between Information Systems that may be written in different languages and use different communiation protocols.
While SOAP uses API contracts to expose it's services and define the way a client can call a service, what Parameters should be sent and what results are to be expected, REST on the other hand has uses no API contracts, for a client to know what services exist and how to call them it should look into the Rest API documentation (this can be defined in a yml file with a OpenAPI or Swagger).
Second SOAP is verbose, it reyes on XML to send a request and describe the services, parameteres and the results returned. On the other hand REST relyed on simple JSON Objects to send requests and receive results. JSON is simple to undersand, lightweight and does not use too much bandwith when sending requests or receiving results.