I'm developing a web app that contains a User entity that is derived from .NET Core's IdentityUser. Lets suppose there is another entity called Comment which has a relation to a user (the user who posted the comment):
public class User : IdentityUser
{
public string SomeExtraField { get; set; }
}
public class Comment
{
//Owner (Creator) of the feedback
public User User { get; set; }
//body of the comment
public string Body { get; set; }
}
Now suppose I have an API endpoint that returns all of the comments in the system. If I query for all comments and include the User relation, when the object gets serialized, everything in the User class is serialized and sent to the client (including the users hashed password, etc). Obviously I don't want this. So I've created a CommentService layer that grabs the Comments from a CommentRepository. From my understanding, the service layer should do the job of mapping the raw Comment object into a Comment DTO, which only contains data that should be sent to the client. I've defined a comment and user DTO like this:
public class UserOutput
{
public string Id { get; set; }
public string SomeExtraField { get; set; }
}
public class CommentOutput
{
public UserOutput User { get; set; }
public string Body { get; set; }
}
Then in my service layer I have something like the following:
//Fetch all comments
var list = await _repository.ListAsync();
//Map comments to DTO
var result = list.Select(x => new CommentOutput
{
Body = x.Body,
User = new UserOutput
{
Id = x.User.Id,
SomeExtraField = x.User.SomeExtraField,
}
});
This all seems to work great. However I can foresee one problem. Lets say I have a large system with Comments, Posts, Likes, Private Messages, etc. I can map them all in a similar fashion above. Then one day I decide to add another field to the UserOutput DTO. Now I have to go through potentially hundreds of mapping code like the sample above to map the new field properly, and whats worse is the compiler wont tell me if I've missed anything. I would like to have a function somewhere that maps a User to a UserOutput but I don't know where it should go.
I've seen some suggestions to put a constructor to the DTO that does the mapping:
public class UserOutput
{
public UserOutput(User user)
{
Id = user.Id;
SomeExtraField = user.SomeExtraField
}
public string Id { get; set; }
public string SomeExtraField { get; set; }
}
but I've seen people against this because it tightly couples the DTO with the Entity. I've also seen suggestions of using Auto Mapper but is also seems an equal amount of people are against it.
Where should I place code that can perform these DTO->entity and entity->DTO mappings so I don't repeat myself all over the place?
Try to check out AutoMapper.
This library will help you to map the Entity Class into the ViewModel.
The way to use it is pretty straightforward.
Related
I want to accept different model type from body based on query param value.
Example:
[HttpGet]
[Route("GetSystemdetails")]
public string Getdeatils([FromBody] SystemDetail sysdetails, string type)
{
//some code here
string details = getdetails(sysdetails);
}
// abc model
public class abc
{
public int UserID { get; set; }
public string Email { get; set; }
}
//xyz model
public class xyz
{
public int xyzid { get; set; }
public string systemval { get; set; }
public string snum { get; set; }
}
type abc and xyz will have it's own model. So based on type I receive in query param I wanted to pick the model and proceed.
Sample url:
localhost/GetSystemdetails/type=abc
localhost/GetSystemdetails/type=xyz
I thought of creating a new model SystemDetail which holds these two models(xyz and abc) and based on system pick them.
I wanted to know what are possible ways to achieve this kind of requirements without creating multiple methods in controller(I don't want to change the format of the URL).
That's not something that's supported out of the box. Your linked solution is probably the closest you'll get to that.
ASP.NET Core is not supposed to take values of the parameters into account when routing, except for validation.
There are several possible ways to do so
Having multiple model objects
As in the link you provided, you can declare multiple model objects. The site has given the example of
public class PostUserGCM
{
public User User { get; set; }
public GCM GCM { get; set; }
}
but you can use your own examples.
Base model
Your models can inherit from some base model. If you only need a single model at a time and they share some similarities, then you could just create a base model which the other two are inheriting from, be agnostic at implementation time and your use cases will mainly differ on instantiation inside the controller, while some service methods could handle other differences.
I am very new to asp.net and C# so bear with me. I am trying to return data from a database using the entity framework .include() method so that I can get the foreign key information from another table. However, what is being returned is only part of the data. It seems to be cut off before everything is returned.
"[{"id":11,"name":"Mr. Not-so-Nice","heroType":3,"heroTypeNavigation":{"id":3,"type":"Villian","heroes":["
Which gives me the error: SyntaxError: Unexpected end of JSON input.
Please seem below for the model classes and the GET section of the controller where this is being returned. If I remove the "include()" method it returns all the heroes from the main table just fine.
public partial class Hero
{
public int Id { get; set; }
public string Name { get; set; }
public int? HeroType { get; set; }
public virtual HeroTypes HeroTypeNavigation { get; set; }
}
{
public partial class HeroTypes
{
public HeroTypes()
{
Heroes = new HashSet<Hero>();
}
public int Id { get; set; }
public string Type { get; set; }
public virtual ICollection<Hero> Heroes { get; set; }
}
// GET: api/Heroes
[HttpGet]
public async Task<ActionResult<IEnumerable<Hero>>> GetHeroesTable()
{
return await _context.HeroesTable.Include(hero => hero.HeroTypeNavigation).ToListAsync();
}
Serializer recursion rules will be tripping this up. Basically as jonsca mentions, you have a circular reference between hero, and hero type. The serializer will start with the hero, then go to serialize the hero type which it will find the Hero's collection and expect to serialize, which each would reference a hero type, with collections of Heros.. The serializer bails when it sees this.
I would recommend avoiding passing back Entity classes to your view to avoid issues with EF and lazy loading. Serialization will iterate over properties, and this will trigger lazy loads. To avoid this, construct a view model for the details your view needs, flatten as necessary.
For example if you want to display a list of Heroes with their Type:
public class HeroViewModel
{
public int HeroId { get; set; }
public string Name { get; set; }
public string HeroType { get; set; }
}
to load:
var heroes = await _context.HeroesTable.Select(x => new HeroViewModel
{
HeroId = x.HeroId,
Name = x.Name,
HeroType = x.HeroType.Type
}).ToListAsync();
You can utilize Automapper for example to help translate entities to view models without that explicit code using ProjectTo<TEntity> which can work with EF's IQueryable implementation.
With larger realistic domains your client likely won't need everything in the object graph.
You won't expose more information than you need to. (I.e. visible via debugging tools)
You'll get a performance boost from not loading the entire graph or triggering
lazy load calls, and it's less data across the wire.
The last point is a rather important one as with complex object graphs, SQL can do a lot of the lifting resulting in a much more efficient query than loading "everything". Lazy hits to the database can easily add several seconds to each and every call from a client, and loading large graphs has a memory implication on the servers as well.
i'm writing a system to track observation values from sensors (e.g. temperature, wind direction and speed) at different sites. I'm writing it in C# (within VS2015) using a code-first approach. Although i've a reasonable amount of programming experience, I'm relatively new to C# and the code-first approach.
I've defined my classes as below. I've built a REST api to accept observation reading through Post, which has driven my desire to have Sensor keyed by a string rather than an integer - Some sensors have their own unique identifier built in. Otherwise, i'm trying to follow the Microsoft Contoso university example (instructors - courses- enrolments).
What I am trying to achieve is a page for a specific site with a list of the sensors at the site, and their readings. Eventually this page will present the data in graphical form. But for now, i'm just after the raw data.
public class Site
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Sensor> Sensors { get; set; }
}
public class Sensor
{
[Key]
public string SensorName { get; set; }
public int SensorTypeId { get; set; }
public int SiteId { get; set; }
public ICollection<Observation> Observations { get; set; }
}
public class Observation
{
public int Id { get; set; }
public string SensorName { get; set; }
public float ObsValue { get; set; }
public DateTime ObsDateTime { get; set; }
}
and I've created a View Model for the page I'm going to use...
public class SiteDataViewModel
{
public Site Site { get; set; }
public IEnumerable<Sensor> Sensors { get; set;}
public IEnumerable<Observation> Observations { get; set; }
}
and then i try to join up the 3 classes into that View Model in the SiteController.cs...
public actionresult Details()
var viewModel.Site = _context.Sites
.Include(i => i.Sensors.select(c => c.Observations));
i used to get an error about "cannot convert lambda expression to type string", but then I included "using System.Data.Entity;" and the error has changed to two errors... on the 'include', I get "cannot resolve method 'include(lambda expression)'...". And on the 'select' i get "Icollection does not include a definition for select..."
There's probably all sorts of nastiness going on, but if someone could explain where the errors are (and more importantly why they are errors), then I'd be extremely grateful.
Simply you can you use like
viewModel.Site = _context.Sites
.Include("Sensors).Include("Sensors.Observations");
Hope this helps.
The way your ViewModel is setup, you're going to have 3 unrelated sets of data. Sites, sensors, and observations. Sites will have no inherent relation to sensors -- you'll have to manually match them on the foreign key. Realistically, your ViewModel should just be a list of Sites. You want to do
#Model.Sites[0].Sensors[0].Observations[0]
not something convoluted like
var site = #Model.Sites[0]; var sensor = #Model.Sensors.Where(s => SiteId == site.Id).Single(); etc...
Try doing
viewModel.Site = _context.Sites.Include("Sensors.Observations").ToList();
Eager-loading multiple levels of EF Relations can be accomplished in just one line.
One of the errors you reported receiving, by the way, is because you're using 'select' instead of 'Select'
And lastly, be aware that eager-loading like this can produce a huge amount of in-memory data. Consider splitting up your calls for each relation, such that you display a list of Sensors, and clicking, say, a dropdown will call an API that retrieves a list of Sites, etc. This is a bit more streamlined, and it prevents you from getting held up because your page is loading so much information.
Update
I've created a sample application for you that you can browse and look through. Data is populated in the Startup.Configure method, and retrieved in the About.cshtml.cs file and the About.cshtml page.. This produces this page, which is what you're looking for I believe.
I'm having a hard time figuring something out that seems as a "easy" problem.
I'm working with Microsoft Azure mobile apps .Net backend, a MSSQL database, Entity Framework code-first and AutoMapper.
So i have the following objects:
public class Route
{
public string Id { get; set; }
[...] //some other properties
public string SerializedGoogleRoute { get; set; }
}
public class DtoRoute
{
public string Id { get; set; }
[...]
public DtoGoogleRoute GoogleRoute { get; set; }
}
public class DtoGoogleRoute
{
[...] //only strings, ints,...
}
So what I want to do is: In the database save the GoogleRoute as a serialized string because it consists of many properties and I don't need them in different columns - I just want it as a serialized string in one column on the route entity.
When the Route object is projected to the DtoRoute object I want the GoogleRoute to be serialized and vice versa.
Because I'm working with LINQ / queryables I am limited to a few AutoMapper mapping options (see AutoMapper wiki). And with none of these I can't get it to work.
The problems I'm facing/what I tried:
I can't serialize/deserialize the string to the DtoGoogleRoute on mapping (with MapFrom or ConstructProjectionUsing) because LINQ obviously cannot transform the JsonConvert.Serialize/Deserialize methods to SQL statements.
I tried having a DtoGoogleRoute property in the Route object and a string property in the DtoRoute object with getters/setters doing the (de)serialization. This works almost perfectly in a custom API controller but because of the OData query filter the azure mobile app .Net backend uses in the tablecontrollers again only the serialized string property gets returned to the client (because OData/LINQ does not know of the other property).
Another option was making a complex type out of DtoGoogleRoute with Entity Framework - this works fine but not with AutoMapper because AutoMapper can't handle complex types.
For now I'm working with a custom API controller and this works. But it would be better to use the tablecontrollers because they support offline sync.
I can't imagine such a simple thing (at least I thought it was a simple thing) can't be done or is so hard to do. But maybe the problem is all the components (tablecontroller, OData, LINQ, EF, AutoMapper) involved.
I would really be thankful if someone could help.
[EDIT]: I think the fact that it works with a normal api controller and not with a tablecontroller has something to do with OData. I tried putting the same code in a tablecontroller method and in an API controller method. when calling the API controller method I can see on the server that it just calls this function and returns all the right properties to the client (checked with fiddler). But when calling the tablecontroller method the tablecontroller method "rewrites" the URL to a OData URL --> I think this is because of some of the EnableQuery or other OData attributes. Because here (although not AutoMapper but it seems like a similar project from Microsoft) it says that the EnableQuery attribute is called twice - also when the request leaves the server. And I think it cuts of the GoogleRoute property because it does not know about this property in the OData metadata or something like that.
You can achieve it like this -
internal class RouteToDtoConverter : TypeConverter<Route, DtoRoute>
{
protected override DtoRoute ConvertCore(Route source)
{
return new DtoRoute
{
Id = source.Id,
GoogleRoute = JsonConvert.DeserializeObject<DtoGoogleRoute>(source.SerializedGoogleRoute)
};
}
}
internal class DtoToRouteConverter : TypeConverter<DtoRoute, Route>
{
protected override Route ConvertCore(DtoRoute source)
{
return new Route
{
Id = source.Id,
SerializedGoogleRoute = JsonConvert.SerializeObject(source.GoogleRoute)
};
}
}
public class Route
{
public string Id { get; set; }
public string SerializedGoogleRoute { get; set; }
}
public class DtoRoute
{
public string Id { get; set; }
public DtoGoogleRoute GoogleRoute { get; set; }
}
public class DtoGoogleRoute
{
public int MyProperty { get; set; }
public int MyProperty2 { get; set; }
}
AutoMapper.Mapper.CreateMap<Route, DtoRoute>()
.ConvertUsing(new RouteToDtoConverter());
AutoMapper.Mapper.CreateMap<DtoRoute, Route>()
.ConvertUsing(new DtoToRouteConverter());
var res = Mapper.Map<DtoRoute>(new Route
{
Id = "101",
SerializedGoogleRoute = "{'MyProperty':'90','MyProperty2':'09'}"
});
var org = Mapper.Map<Route>(res); //pass
I am working with an EF Code First project, and all is well. I have a simple Class, Customer. In my Customer Class I have a field I want to encrypt (Yes, I know I can encrypt at the DB level but requirements dictate I encrypt at the Domain/Code level), so I am hoping that I can do something like the following:
public class Customer
{
public int CustomerID { get; set; }
public string FieldToEncrypt { get; set { _FieldToEncrypt = MyEncryptionFunction.Encrypt(); } }
}
However, I assume that if the setter has a definition, entity framework code first may ignore that property when generating the schema. So my question is, is there a way to do EF Code First with provided getters/setters, or should I move this functionality into a constructor? Should I override one of the methods/events that happens when the Context is saving, instead?
EDIT ********************
As a note, I am using DataService to transmit the data over an OData protocol service. This automatically generates insert/update/select methods. Some of the suggestions require creating a second property, but the DataService class does not seem to pass through NotMapped properties. This throws a bit of a kink into my earlier question.
public class Customer
{
public int CustomerID { get; set; }
public string EncryptedField { get; private set; }
[NotMapped]
public string Field
{
get { return MyEncryptionFunction.Decrypt(EncryptedField); }
set { EncryptedField = MyEncryptionFunction.Encrypt(value); }
}
}