I'm developing a Xamarin.iOS application which will connect to a web service via a RESTful API. I am currently writing the response and business objects for the API client layer, but I have run into a problem.
Consider the following two sample API results:
Successful
{
"data":{
"id":"gwaMR",
"animated":false,
"size":11762,
"link":"http:\/\/i.imgur.com\/gwaMR.jpg"
},
"success":true,
"status":200
}
Erroneous
{
"data":{
"error":"Unable to find an image with the id, vycVV",
"request":"\/3\/image\/vycVV",
"method":"GET"
},
"success":false,
"status":404
}
Because both the successful data information as well as the error details both share the "data" key in their respective scenarios, I have written the following objects in C#:
public class BaseBusinessObject<D> where D:BaseBusinessObjectData
{
public D Data { get; set; }
public int Status { get; set; }
public bool Success { get; set; }
}
public class BaseBusinessObjectData
{
public string Error { get; set; }
public string Method { get; set; }
public string Request { get; set; }
}
public class ImageObject : BaseBusinessObject<ImageObjectData>
{
}
public class ImageObjectData : BaseBusinessObjectData
{
public string ID { get; set; }
public bool Animated { get; set; }
public int Size { get; set; }
public string Link { get; set; }
}
When making the API call (using automatic object deserialization with RestSharp), I provide the object type ImageObject as the expected result type. However, I'm not actually able to get that far yet. When attempting to compile those response object types, I get the following error:
/Users/willseph/GitHub/Repos/AppName/API/API.cs(46,255+): Error
CS0305: Using the generic type `AppName.BaseBusinessObject'
requires `1' type argument(s) (CS0305)
However, when I take this same code and bring it into a standard C# library (still within Xamarin Studio), it compiles just fine.
As a workaround, I am able to remove generics from my code by using hiding and a new Data member:
public class BaseBusinessObject
{
public BaseBusinessObjectData Data { get; set; }
public int Status { get; set; }
public bool Success { get; set; }
}
public class BaseBusinessObjectData
{
public string Error { get; set; }
public string Method { get; set; }
public string Request { get; set; }
}
public class ImageObject : BaseBusinessObject
{
public new ImageObjectData Data { get; set; }
}
public class ImageObjectData : BaseBusinessObjectData
{
public string ID { get; set; }
public string Link { get; set; }
public int Size { get; set; }
public bool Animated { get; set; }
}
This compiles fine and results in expected behavior. Does anyone have any insight on what may be causing this issue?
I tried adding a separate temporary file alongside my workaround containing the original erroneous classes (though renamed to not cause conflict), and it appears to be compiling.
I'm not sure what the issue was, but I suppose it was some strange fluke or anomaly caused by my computer.
Related
Firstly, apologies if this seems basic, I am new to C#/dotnet and if the answer to this questions is somewhere obvious please point me in the right direction.
I have a DTO class with the following code
public class LessonDetailView : BaseResult
{
public long Id { get; set; }
public string Title { get; set; }
public List<LessonImagesListView> LessonImages { get; set; }
public List<LessonInstructionCardListView> InstructionCards { get; set; }
}
public class LessonImagesListView
{
public long Id { get; set; }
public string Title { get; set; }
public ImageDetailView Image { get; set; }
public LessonImagesListView()
{
Image = new ImageDetailView();
}
}
public class LessonInstructionCardListView
{
public long Id { get; set; }
public string Instructions { get; set; }
}
So I have 2 distinct types of object that I attach to the lesson and send to the frontend.
I will add that in the future I might have 6 different types of object.
These Images, or Instructions are also going to be displayed in a certain order on the front end so instead of sending them all separately I wanted to combine them all and send them in a new List LessonAssetsListView for example.
How can i create Lists in a DTO that combine 2 other lists ?
OR ... is this something I even need to do here ... and can i just do all this in my service.
Help appreciated.
You could simply define a type that composes both your existing and send a List of them
public class LessonAsset
{
public LessonImagesListView Image {get;set; }
public LessonInstructionCardListView Instruction {get;set;}
}
and then
public class LessonDetailView : BaseResult
{
public long Id { get; set; }
public string Title { get; set; }
public List<LessonAsset> LessonAssets { get; set; }
}
There's a lot of Qs on this, but I need a solution without JSON.Net, etc. - I must use the canned stuff in Asp.Net MVC.
How can I serialize a POCO with a dynamic property - and get all the static properties, too? What I found was the dynamic only, or the static type which is easy.
e.g.
public class ReturnThisClassAsJSON {
public int Id {get; set; }
public string Name { get; set; }
public ContainedClass ContainedContents { get; set; }
}
public class ContainedClass {
public int Order { get; set; }
public string Label { get; set; }
public dynamic DynamicInfo { get; set; }
public List<dynamic> DynamicList { get; set }
}
My own answer:
I replaced the dynamic from the DynamicInfo and DynamicList from the ContainedClass with static types.
With the dynamic, I had 1 of 2 choices. Either serialize the dynamic to a string in its own serialization call using above SO question 5156664. (Which left me with the rest of the class I also wanted serialized and merged with it, thus this question). Or, incur this error:
"A circular reference was detected while serializing an object of type 'System.Reflection .RuntimeModule' ".
when attempting a single serialization call on the ContainedClass.
So, I transferred the dynamics into static-typed classes:
public class ColumnValue
{
public string Name { get; set; }
public string Value { get; set; }
}
public class DynamicRow
{
public List<ColumnValue> ColumnValue { get; set; }
}
and, change ContainedClass to this:
public class ContainedClass
{
public List<ColumnValue> DynamicInfo { get; set; }
public List<DynamicRow> Data { get; set; }
}
And, it serializes using out-of-the-box Asp.Net MVC:
return Json(ReturnThisClassAsJSON, JsonRequestBehaviour.AllowGet);
EDIT: I originally worded this question very poorly, stating the problem was with JSON serialization. The problem actually happens when I'm converting from my base classes to my returned models using my custom mappings. I apologize for the confusion. :(
I'm using .NET Core 1.1.0, EF Core 1.1.0. I'm querying an interest and want to get its category from my DB. EF is querying the DB properly, no problems there. The issue is that the returned category has a collection with one interest, which has one parent category, which has a collection with one interest, etc. When I attempt to convert this from the base class to my return model, I'm getting a stack overflow because it's attempting to convert the infinite loop of objects. The only way I can get around this is to set that collection to null before I serialize the category.
Interest/category is an example, but this is happening with ALL of the entities I query. Some of them get very messy with the loops to set the relevant properties to null, such as posts/comments.
What is the best way to address this? Right now I'm using custom mappings that I wrote to convert between base classes and the returned models, but I'm open to using any other tools that may be helpful. (I know my custom mappings are the reason for the stack overflow, but surely there must be a more graceful way of handling this than setting everything to null before projecting from base class to model.)
Classes:
public class InterestCategory
{
public long Id { get; set; }
public string Name { get; set; }
public ICollection<Interest> Interests { get; set; }
}
public class Interest
{
public long Id { get; set; }
public string Name { get; set; }
public long InterestCategoryId { get; set; }
public InterestCategory InterestCategory { get; set; }
}
Models:
public class InterestCategoryModel
{
public long Id { get; set; }
public string Name { get; set; }
public List<InterestModel> Interests { get; set; }
}
public class InterestModel
{
public long Id { get; set; }
public string Name { get; set; }
public InterestCategoryModel InterestCategory { get; set; }
public long? InterestCategoryId { get; set; }
}
Mapping functions:
public static InterestCategoryModel ToModel(this InterestCategory category)
{
var m = new InterestCategoryModel
{
Name = category.Name,
Description = category.Description
};
if (category.Interests != null)
m.Interests = category.Interests.Select(i => i.ToModel()).ToList();
return m;
}
public static InterestModel ToModel(this Interest interest)
{
var m = new InterestModel
{
Name = interest.Name,
Description = interest.Description
};
if (interest.InterestCategory != null)
m.InterestCategory = interest.InterestCategory.ToModel();
return m;
}
This is returned by the query. (Sorry, needed to censor some things.)
This is not .NET Core related! JSON.NET is doing the serialization.
To disable it globally, just add this during configuration in Startup
services.AddMvc()
.AddJsonOptions(options =>
{
options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
}));
edit:
Is it an option to remove the circular references form the model and have 2 distinct pair of models, depending on whether you want to show categories or interests?
public class InterestCategoryModel
{
public long Id { get; set; }
public string Name { get; set; }
public List<InterestModel> Interests { get; set; }
public class InterestModel
{
public long Id { get; set; }
public string Name { get; set; }
}
}
public class InterestModel
{
public long Id { get; set; }
public string Name { get; set; }
public InterestCategoryModel InterestCategory { get; set; }
public class InterestCategoryModel
{
public long Id { get; set; }
public string Name { get; set; }
}
}
Note that each of the models has a nested class for it's child objects, but they have their back references removed, so there would be no infinite reference during deserialization?
I am getting a rather weird casting error. Here is the code:
public class OrganizationLocation : IOrganizationLocation
{
public Guid Id { get; set; }
public string Name { get; set; }
}
public interface IOrganizationLocation
{
string Name { get; }
}
public class Organization : IOrganization
{
public Guid Id { get; set; }
public string Alias { get; set; }
public virtual ICollection<OrganizationLocation> Location { get; set; }
public ICollection<IOrganizationLocation> Locations
{
get
{
return (ICollection<IOrganizationLocation>) Location;
}
}
}
public interface IOrganization
{
string Alias { get; }
ICollection<IOrganizationLocation> Locations { get; }
}
now when I try to run this via a service (backend data layer is EF6), the "Location" variable has all the values, however, the "Locations" variable fails to cast. If I try to do a safe cast, it comes back as null every time.
I'm not understanding why would the cast fail? It has same fields, both are ICollection Type, so why do I get a HashSet?
The reason why I am doing it this way is because for EF6 framework to be able to treat this class as a table it needs to have a concrete type and a public get/set. However, I do not wish to expose that, so I use interface instead and then inject the class when the interface is called. This way I only expose get method and on top of it I only expose interface layers.
Unable to cast object of type 'System.Collections.Generic.HashSet`1[Namespace.OrganizationLocation]' to type 'System.Collections.Generic.ICollection`1[Namespace2.IOrganizationLocation]'.
I was able to resolve this by changing the code to the following:
public class OrganizationLocation : IOrganizationLocation
{
public Guid Id { get; set; }
public string Name { get; set; }
}
public interface IOrganizationLocation
{
string Name { get; }
}
public class Organization : IOrganization
{
public Guid Id { get; set; }
public string Alias { get; set; }
public virtual ICollection<OrganizationLocation> Location { get; set; }
public IEnumerable<IOrganizationLocation> Locations => Location
}
public interface IOrganization
{
string Alias { get; }
IEnumerable<IOrganizationLocation> Locations { get; }
}
Continuing to develop the API I have mentioned in previous posts, I have come across the following situation:
I need to be able to access a list of responses returned by the
webservice.
Problem is I am unsure how to implement IEnumerable on this class.
...
public class ResponseBodyResponse
{
public ResponseListResponse ResponseList { get; set; }
public class ResponseListResponse
{
public ResponseInfoResponse ResponseInfo { get; set; }
public class ResponseInfoResponse
{
public string RequestId { get; set; }
public string RequestType { get; set; }
public DateTime RequestDate { get; set; }
public string RequestStatus { get; set; }
public string Error { get; set; }
public string Memo { get; set; }
}
public ResponseListResponse()
{
ResponseInfo = new ResponseInfoResponse();
}
}
public ResponseBodyResponse()
{
ResponseList = new ResponseListResponse();
}
...
Before anyone asks I did get a copy of the xsd files, however generating the classes using xsd.exe resulted in a ridiculous mishmash of files with conflicting class names causing over 1000 ambiguous naming errors.
You really should return a concrete collection such as a list or an array from a web service instead of an implementation IEnumerable<T>, even though lists and arrays (and other colections) do implement it. Its not IEnumerable<T> that is the key for the serialization.
Aside, the nested class structure makes your code hard to consume.
Since I'm not sure of your intent with your above code, here is an example
public class Road
{
public Car[] Cars { get; set; } // this can be also `List<Car>`
}
public class Car
{
// stuff
}