I need to convert my custom class (c#) object into OData Json format and then convert it back to my object. Is there any library available to do this. I need something similar to the Newtonsoft.Json.
For example:
string json = Newtonsoft.Json.JsonConvert.SerializeObject(myObject);
Scenario (If you need to know):
I am using Windows Azure Table Storage to save my objects. Client can save any kind of object (azure table storage limitations apply). Client will only connect to my service (ServiceStack) deployed as a web role on Windows Azure Cloud. This service will process the client request e.g. authenticate/authorize and then will connect to the table storage to save the object sent by client.
The main thing is my service (ServiceStack deployed as web role) doesn't know the class type of the object being sent by the client because client can create any new class and send its object for persistence. Windows Table Storage REST API supports OData. I am writing an SDK for client to send request to my service (web role). SDK will send the request after serializing the object into OData format so that my service can understand its schema as well.
Unfortunately, OData does NOT have serializer and deserializer independent of edm model. OData only serialize and deserialize objects when you have a model defining them, since you must convert the objects into values in OData format with the model.
Have you considered to use Azure Table SDK for .NET? AFAIK, Azure Table support self-defined types in the storage.
Plus, if you really need to do the serialization of your client objects, it seems you just need to serialize them on the client, then store the serialized strings in Azure Table. When you need to consume them, you can get the strings from Azure Table then deserialize them on your client.
Related
There are a lot of answers on how to convert ODataQuery into an Expression or into a Lambda, but what I need is quite the opposite, how to get from a Linq Expression the OData query string.
Basically what I want is to transcend the query to another service. For example, having 2 services, where your first service is not persisting anything and your second service is the one that will return the data from a database. Service1 sends the same odata request to Service2 and it can add more parameters to the original odata request to Service2
What I would like:
public IActionResult GetWeatherForecast([FromServices] IWeatherForcastService weatherForcastService)
{
//IQueryable here
var summaries = weatherForcastService.GetSummariesIQ();
var url = OdataMagicHelper.ConvertToUri(summaries);
var data = RestClient2.Get(url);
return data;
}
OP Clarified the request: generate OData query URLs from within the API itself.
Usually, the queries are so specific or simple, that it's not really necessary to try and generate OData urls from within the service, the whole point of the service configuration is to publish how the client could call anything, so it's a little bit redundant or counter-intuitive to return complex resource query URLs from within the service itself.
We can use Simple.OData.Client to build OData urls:
If the URL that we want to generate is:
{service2}/api/v1/weather_forecast?$select=Description
Then you could use Simple.OData.Client:
string service2Url = "http://localhost:11111/api/v1/";
var client = new ODataClient(service2Url);
var url = await client.For("weather_forecast")
.Select("Description")
.GetCommandTextAsync();
Background, for client-side solutions
If your OData service is a client for another OData Service, then this advice is still relevant
For full linq support you should be using OData Connected Services or Simple.OData.Client. You could roll your own, or use other derivatives of these two but why go to all that effort to re-create another wheel.
One of the main drivers for a OData Standard Compliant API is that the meta data is published in a standard format that clients can inspect and can generate consistent code and or dynamic queries to interact with the service.
How to choose:
Simple.OData.Client provides a lightweight framework for dynamically querying and submitting data to OData APIs. If you already have classes that model the structure of the API then you can use typed linq style query syntax, if you do not have a strongly typed model but you do know the structure of the API, then you can use either the untyped or dynamic expression syntax to query the API.
If you do not need full compile-time validation of your queries or you already have the classes that represent the resources served by the API then this is a simple enough interface to use.
This library is perfect for use inside your API logic if you have need of generating complex URLs in a strongly typed style of code without trying to generate a context to manage the connectivity to the server.
NOTE: Simple.OData.Client is sometimes less practical when developing against a large API that is rapidly evolving or that does not have a strict versioned route policy. If the API changes you will need to diligently refactor your code to match and will have to rely on extensive regression testing.
OData Connected Services follows a pattern where some or all of the API is modelled in the client with strongly typed client side proxy interfaces. These are POCO classes that have the structure necessary to send to and receive data from the server.
The major benefit to this method is that the POCO structures, requests and responses are validated against the schema of the API. This effectively gives you full intellisense support for the API and allows you to explor it's structure, the generated code becomes your documentation. It also gives you compile time checking and runtime safety.
The general development workflow after the API is deployed or updated is:
Download the $metadata document
Select the Operations and Types from the API that you want to model
Generate classes to represent the selected DTO Types as defined in the document, so all the inputs and outputs.
Now you can start using the code.
In VS 2022/19/17 the Connected Services interface provides a simple wizard for establishing the initial connection and for updating (or re-generating) when you need to.
The OData Connected Service or other client side proxy generation pattern suits projects under these criteria:
The API definition is relatively stable
The API definition is in a state of flux
You consume many endpoints
You don't want to manually code the types to serialize or deserialze payloads
Full disclosure, I prefer the connected service approach, but I have my own generation scripts. However if you are trying to generate OData query urls from inside your API, its not really an option, it creates a messy recursive dependency... just don't go there.
Connected services is the low-(manual)-code and lazy approach that is perfect for a stable API, generate once and never do it again. But the Connected Service architecture is perfect for a rapidly changing API because it will manage the minute changes to the classes for you, you just need to update your client side proxy classes more frequently.
I am writing an application that is consuming an in-house WCF-based REST service and I'll admit to being a REST newbie. Since I can't use the "Add Service Reference", I don't have ready-made proxy objects representing the return types from the service methods. So far the only way I've been able to work with the service is by sharing the assembly containing the data types exposed by the service.
My problem with this arrangment is that I see only two possibilities:
Implement DTOs (DataContracts) and expose those types from my service. I would still have to share an assembly but this approach would limit the types contained in the assembly to the service contract and DTOs. I don't like to use DTOs just for the sake of using them, though as they add another layer of abstraction and processing time to convert from domain object to DTO and vice versa. Plus, if I want to have business rules, validation, etc. on the client, I'd have to share the domain objects anyways, so is the added complexity necessary.
Support serialization of my domain objects, expose those types and share that assembly. This would allow me to share business and validation logic with the client but it also exposes parts of my domain objects to the client that are meant only for the service app.
Perhaps an example would help the discussion...
My client application will display a list of documents that is obtained from the REST service (a GET operation). The service returns an array of DocumentInfo objects (lightweight, read-only representation of a Document).
When the user selects one of the items, the client retrieves the full Document object from the REST service (GET by id) and displays a data entry form so the user can modify the object. We would want validation rules for a rich user experience.
When the user commits the changes, the Document object is submitted to the REST service (a PUT operation) where it is persisted to the back-end data store.
If the state of the Document allows, the user may "Publish" the Document. In this case, the client POSTs a request to the REST service with the Document.ID value and the service performs the operation by retrieving the server-side Document domain object and calling the Publish method. The Publish method should not be available to the client application.
As I see it, my Document and DocumentInfo objects would have to be in a shared assembly. Doing this makes Document.Publish available to the client. One idea to hide it would be to make the method internal and add an InternalsVisibleTo attribute that allows my service app to call the method and not the client but this seems "smelly."
Am I on the right track or completely missing something?
The classes you use on the server should not be the same classes you use on the client (apart from during the data transfer itself). The best approach is to create a package (assembly/project) containing DTOs, and share these between the server and the client. You did mention that you don't want to create DTO's for the sake of it, but it is best practice. The performance impact of adding extra layers is negligible, and layering actually helps make your application easier to develop and maintain (avoiding situations like yours where the client has access to server code).
I suggest starting with the following packages:
Service: Resides on server only, exposes the service and contains server application logic.
DTO: Resides on both server and client. Contains simple classes which contain data which need to be passed between server and client. Classes have no code apart from properties. These are short lived objects which survive long enough only to transfer data.
Repository: Resides on client only. Calls the server, and turns Model objects into DTO's (and vice versa).
Model: Resides on client only. Contains classes which represent business objects and relationships. Model objects stay in memory throughout the life of the application.
Your client application code should call into Repository to get Model objects (you might also consider looking into MVVM if your not sure how to go about this).
If your service code is sufficiently complex that it needs access to Model classes, you should create a separate Model package (obviously give it a different name) - the only classes which should exist both on server and client are DTO classes.
I thought that I'd post the approach I took while giving credit to both Greg and Jake for helping guide me down the path.
While Jake is correct that deserializing the data on the client can be done with any type as long as it implements the same data contract, enforcing this without WSDL can be a bit tricky. I'm in an environment where other developers will be working with my solution both to support and maintain the existing as well as creating new clients that consume my service. They are used to "Add Service Reference" and going.
Greg's points about using different objects on the client and the server were the most helpful. I was trying to minimize duplicate by sharing my domain layer between the client and the server and that was the root of my confusion. As soon as I separated these into two distinct applications and looked at them in isolation, each with their own use cases, the picture became clearer.
As a result, I am now sharing a Contracts assembly which contains my service contracts so that a client can easily create a channel to the server (using WCF on the client-side) and data contracts representing the DTOs passed between client and service.
On the client, I have ViewModel objects which wrap the Model objects (data contracts) for the UI and use a service agent class to communicate with the service using the service contracts from the shared assembly. So when the user clicks the "Publish" button in the UI, the controller (or command in WPF/SL) calls the Publish method on the service agent passing in the ID of the document to publish. The service agent relays the request to the REST API (Publish operation).
On the server, the REST API is implemented using the same service contracts. In this case, the service works with my domain services, repositories and domain objects to carry out the tasks. So when the Publish service operation is invoked, the service retrieves the Document domain object from the DocumentRepository, calls the Publish method on the object which updates the internal state of the object and then the service passes the updated object to the Update method of the repository to persist the changes.
I am pleased with the outcome as I believe this gives me a more robust and extensible architecture to work with. I can change the ViewModels as needed to support the UI with no concern over poluting the service(s) and, likewise, change the internal implementation of the service operations (domain layer) without affecting the client application(s). All that binds the two are the contracts they share. Pretty clean.
You can serialize your domain objects and then de-serialize them into different types on the client. Both types need to implement the same data contract. All serializable types have at least a default data contract that includes all public read/write properties and fields.
I have to develop an application to store some flat files in the DB.. The Console application and the SQL Server will be on the same machine, which of these two options is the best?
Create WCF Data Services and use it from the console app
Use directly the Entity Framework entities from the console app
Generally, when it is better to use WCF Data Services or Entity Framework?
THANKS!
Those are two totally different technologies:
Entity Framework is an OR mapper to make your database access easier; you can compare this to e.g. NHibernate, Linq-to-SQL, Subsonic, Genome, or other OR mappers
WCF Data Services is a way to expose your data models to the outside world over HTTP/REST; compare this to legacy ASMX webservices, pure WCF services, other service technologies
You cannot compare the two - they're totally different beasts, and in many solutions, they will be working together - one cannot replace the other.
If you have a console app that needs to read data from a database, you can either use Entity Framework directly - in that case, your console app must have a direct connection to the database, and it's tied to the Entity Framework technology.
The option of exposing the data using a WCF Data Service adds another layer - your console app doesn't access the data directly, but it just calls a WCF Data Service. Now you basically have two parts: your console app as the client, and some kind of a service app that will provide the data. In that case, your client doesn't need to know anything about Entity Framework or anything like that - you could also easily add a second client, e.g. a web app. But the service app that provides the data will still need to be able to directly connect to the database using Entity Framework.
So in the end, you're not really replacing Entity Framework with WCF Data Services - you're just adding another layer of indirection, but in the end, to get at the data, you still need some kind of data access technology (like Entity Framework).
I'm working on a simple plug-in framework. WCF client need to create an instance of 'ISubject' and then send back to service side. The 'ISubject' can be extended by the user. The only thing client knows at runtime is ID of a subclass of 'ISubject'.
Firstly, client need to get type information of a specific subclass of 'ISubject'. Secondly, client using reflection to enumerate all members to create a custom property editor so that each member can be asigned with proper value. Lastly, client create an instance of that subclass and send back to service.
The problem is how does client get the type information through WCF communication?
I don't want client to load that assembly where the subclass (of 'ISubject') exists.
Thanks
First, you need to be aware that there is no magic way that WCF will provide any type information to your client in the scenario you have descibed. If you are going to do it, you will have to provide a mechanism yourself.
Next, understand that WCF does not really pass objects from server to client or vice versa. All it passes are XML infosets. Often, the XML infoset passed includes a serialized representation of some object which existed on the sender's side; in this case, if the client knows about that type (i.e. can load the type's metadata from its assembly), it can deserialize the XML to instantiate an identical object on the client side. If the client doesn't have the type metadata, it can't: this is the normal case with WCF unless data contract types are in assemblies shared by both server and client implementations (generally not a good idea).
The way WCF is normally used (for example if the client is implemented using a "Service Reference" in Visual Studio), what happens is that the service publishes WSDL metadata describing its operations and the XML schemas for the operation parameters and return values, and from these a set of types is generated for use in the client implementation. These are NOT the same .NET types as the data contract types used by the service implementation, but they are "equivalent" in the sense that they can be serialized to the same XML data passed over the network. Normally this type generation is done at design time in Visual Studio.
In order to do what you are trying to do, which is essentially to do this type generation at runtime, you will need some mechanism by which the client can get sufficient knowledge of the structure of the XML representing the various types of object implementing ISubject so that it can understand the XML received from the service and generate the appropriate XML the service is expecting back (either working with the XML directly, or deserializing/serializing it in some fashion). If you really, really want to do this, possible ways might be:
some out-of-band mechanism whereby the client is preconfigured with the relevant type information corresponding to each subclass of ISubject that it might see. The link provided in blindmeis's answer is one way to do that.
provide a separate service operation by which the client can translate the ID of the subclass to type metadata for the subclass (perhaps as an XSD schema from which the client could generate a suitable serializable .NET type to round trip the XML).
it would also be feasible in principle for the service to pass type metadata in some format within the headers of the response containing the serialized object. The client would need to read, interpret and act on the type infomation in an appropriate fashion.
Whichever way, it would be a lot of effort and is not the standard way of using WCF. You will have to decide if it's worth it.
I think you might be missing something :)
A major concept with web services and WCF is that we can pass our objects across the network, and the client can work with the same objects as the server. Additionally, when a client adds a service reference in Visual Studio, the server will send the client all the details it needs to know about any types which will be passed across the network.
There should be no need for reflection.
There's a lot to cover, but I suggest you start with this tutorial which covers WCF DataContracts - http://www.codeproject.com/KB/WCF/WCFHostingAndConsuming.aspx
To deserialize an object the receiving side will need to have the assembly the type is defined in.
Perhaps you should consider some type of remoting or proxying setup where the instance of ISubject lives on one side and the other side calls back to it. This may be problematic if you need to marshal large amounts of data across the wire.
wcf needs to know the real object(not an interface!) which should be sent across the wire. so you have to satisfy the server AND the clientproxy side from the WCF service that they know the types. if you dont know the object type while creating the WCF service, you have to find a way to do it in a dynamic way. i use the solution from here to get the knownTypes to my WCF service.
[ServiceContract(SessionMode = SessionMode.Required]
[ServiceKnownType("GetServiceKnownTypes", typeof(KnownTypeHelper))]//<--!!!
public interface IWCFService
{
[OperationContract(IsOneWay = false)]
object DoSomething(object obj);
}
if you have something "universal" like the code above, you have to be sure that whatever your object at runtime will be, your WCF service have to know this object.
you wrote your client create a subclass and sent it back to the service. if you want to do that, WCF(clientproxy and server!) needs to know the real type of your subclass.
How do I transfer an object in RESTful web service? it seems like RESTful only supports string to exchange data between client and service. thanks
All web services only support the transfer of a representation of objects. Given the right client, you can easily generate objects with the information passed. For example, using JSON and a javascript client with jQuery, you can easily call jQuery.parseJSON(stringFromRESTServer); (or any number of methods in other good js libraries) to get a js object.