In some cases there is a need to return composite DTOs from our repository, where the DTO just has a few properties that are Model properties and the function of the DTO is just to be a simple composite object (returning a Queryable is not enough because there is more information than T)
For example:
Model:
public class Job
{
int Id { get; set; }
//more properties
}
public class JobApplication
{
int Id { get; set; }
//more properties
}
Repository:
IQueryable<JobAndUserApplication> GetJobAndMatchingUserApplication(int userId):
public class JobAndUserApplication
{
public Job Job { get; set; }
public JobApplication JobApplication { get; set; }
}
Now - Id like to simply do (Project and To are Automapper functionality):
//this allows one efficient query to bring in the subproperties of the composite DTO
var jobVmList = jobRepository.GetAllJobsAndMatchingJobApplicationByUser(userId)
.Project()
.To<JobVM>()
.ToList();
So I need a mapping kind of like this:
Mapper.CreateMap<JobAndUserApplication, JobVM>()
.ForMember(jvm => jvm, opt => opt.ResolveUsing(src => src.Job));
//many other .ForMembers that are not relevant right now
I am attempting to map the Job property of the DTO directly on to the JobVM (which shares many of the same properties).
My mapping throws the following exception:
Custom configuration for members is only supported for top-level individual members on a type.
What am I doing wrong and how can I accomplish the mapping form the Job property of the DTO on the the JobVM itself?
Thanks
Automapper is telling you that you can only define custom actions on a member (property) of a class, not on the class itself. What you need to do is first create a Job to JobVM map:
Mapper.CreateMap<Job, JobVM>()
and
Mapper.CreateMap<JobAndUserApplication, JobVM>()
being sure to ignore and set any duplicate properties across the two types. Then run automapper twice, first from the child object:
var jobVM = Mapper.Map<Job, JobVM>(jobAndUserApplication.job);
then from the parent object
Mapper.Map<JobAndUserApplication, JobVM>(jobAndUserApplication, jobVM );
Or the other way around, depending on how your properties are laid out.
Quick side note: I have a feeling you might be mixing concerns, and my code smell alarm is going off. I'd take a second look at either your viewmodel or domain model, as this is not a typical issue I see come up. (just my $0.02 :-)
Related
Background
I have a class that looks more or less like this:
public class MyClass
{
[Id]
public long Id { get; set; }
public string MyProperty { get; set; }
public bool MyBoolean { get; set; }
public string AnotherProperty { get; set; }
public MyClass ChildOne { get; set; }
public MyClass ChildTwo { get; set; }
}
I will need to use a stored procedure to load a set of records, but that's ok as long as the structure itself is correct.
For any instance of MyClass, one or both of the children can be null. Any instance of MyClass can be used in a parent class - but the child itself doesn't need to know about this relationship, and a child can be used by any number of parents.
Problem
With this structure, I get the following error when creating a new migration:
Unable to determine the principal end of an association between the
types 'MyClass' and 'MyClass'. The principal end of this association
must be explicitly configured using either the relationship fluent API
or data annotations.
This error makes sense - when given a structure of an object with a foreign key to itself, I am not surprised that EF has a hard time determining the principal end. I'm not sure how to fix this, though.
I've tried some different Fluent mappings:
modelBuilder.Entity<MyClass>().HasOptional(x => x.ChildOne).WithOptionalPrincipal(x => x.ChildOne);
modelBuilder.Entity<MyClass>().HasOptional(x => x.ChildOne).WithOptionalDependent(x => x.ChildOne);
modelBuilder.Entity<MyClass>().HasOptional(x => x.ChildOne);
(Note: I didn't try these concurrently - I did one at a time & duplicated it for ChildTwo.)
I was able to get a migration to work by adding a ChildThree property to MyClass, but that doesn't make sense and isn't a useful property; it just creates another foreign key on the table but this isn't needed in my model.
So, in summary:
How do I get this structure to work the way I want? I think the secret is in some Fluent mapping voodoo but I'm very unfamiliar with that library and I don't know how to get that to work.
Why does adding a third (unneeded, unwanted) property fix everything and allow the migration to scaffold?
Your fluent mapping is totally wrong.
You should do something like this:
modelBuilder.Entity<MyClass>().HasOptional(p => p.ChildOne).WithOptionalDependent();
modelBuilder.Entity<MyClass>().HasOptional(p => p.ChildTwo).WithOptionalDependent();
Consider having a ViewModel:
public class ViewModel
{
public int id { get; set; }
public int a { get; set; }
public int b { get; set; }
}
and an original Model like this:
public class Model
{
public int id { get; set; }
public int a { get; set; }
public int b { get; set; }
public int c { get; set; }
public virtual Object d { get; set; }
}
Each time I get the view model I have to put all ViewModel properties one by one into Model. Something like:
var model = Db.Models.Find(viewModel.Id);
model.a = viewModel.a;
model.b = viewModel.b;
Db.SaveChanges();
Which always cause lots of problems. I even sometimes forget to mention some properties and then disaster happens!
I was looking for something like:
Mapper.Map(model, viewModel);
BTW: I use AutoMapper only to convert Model to ViewModel but vice-versa I always face errors.
Overall that might be not the answer, that you are looking for, but here's a quote from AutoMapper author:
I can’t for the life of me understand why I’d want to dump a DTO
straight back in to a model object.
I believe best way to map from ViewModel to Entity is not to use AutoMapper for this. AutoMapper is a great tool to use for mapping objects without using any other classes other than static. Otherwise, code gets messier and messier with each added service, and at some point you won't be able to track what caused your field update, collection update, etc.
Specific issues often faced:
Need for non-static classes to do mapping for your entities
You might need to use DbContext to load and reference entities, you might also need other classes - some tool that does image upload to your file storage, some non-static class that does hashing/salt for password, etc etc... You either have to pass it somehow to automapper, inject or create inside AutoMapper profile, and both practices are pretty troublemaking.
Possible need for multiple mappings over same ViewModel(Dto) -> Entity Pair
You might need different mappings for same viewmodel-entity pair, based on if this entity is an aggregate, or not + based on if you need to reference this entity or reference and update. Overall this is solvable, but causes a lot of not-needed noise in code and is even harder to maintain.
Really dirty code that's hard to maintain.
This one is about automatic mapping for primitives (strings, integers, etc) and manual mapping references, transformed values, etc. Code will look really weird for automapper, you would have to define maps for properties (or not, if you prefer implicit automapper mapping - which is also destructive when paired with ORM) AND use AfterMap, BeforeMap, Conventions, ConstructUsing, etc.. for mapping other properties, which complicates stuff even more.
Complex mappings
When you have to do complex mappings, like mapping from 2+ source classes to 1 destination class, you will have to overcomplicate things even more, probably calling code like:
var target = new Target();
Mapper.Map(source1, target);
Mapper.Map(source2, target);
//etc..
That code causes errors, because you cannot map source1 and source2 together, and mapping might depend on order of mapping source classes to target. And I'm not talking if you forget to do 1 mapping or if your maps have conflicting mappings over 1 property, overwriting each other.
These issues might seem small, but on several projects where I faced usage of automapping library for mapping ViewModel/Dto to Entity, it caused much more pain than if it was never used.
Here are some links for you:
Jimmy Bogard, author of AutoMapper about 2-way mapping for your entities
A small article with comments about problems faced when mapping ViewModel->Entity with code examples
Similar question in SO: Best Practices For Mapping DTO to Domain Object?
For this purpose we have written a simple mapper. It maps by name and ignores virtual properties (so it works with entity framework). If you want to ignore certain properties add a PropertyCopyIgnoreAttribute.
Usage:
PropertyCopy.Copy<ViewModel, Model>(vm, dbmodel);
PropertyCopy.Copy<Model, ViewModel>(dbmodel, vm);
Code:
public static class PropertyCopy
{
public static void Copy<TDest, TSource>(TDest destination, TSource source)
where TSource : class
where TDest : class
{
var destProperties = destination.GetType().GetProperties()
.Where(x => !x.CustomAttributes.Any(y => y.AttributeType.Name == PropertyCopyIgnoreAttribute.Name) && x.CanRead && x.CanWrite && !x.GetGetMethod().IsVirtual);
var sourceProperties = source.GetType().GetProperties()
.Where(x => !x.CustomAttributes.Any(y => y.AttributeType.Name == PropertyCopyIgnoreAttribute.Name) && x.CanRead && x.CanWrite && !x.GetGetMethod().IsVirtual);
var copyProperties = sourceProperties.Join(destProperties, x => x.Name, y => y.Name, (x, y) => x);
foreach (var sourceProperty in copyProperties)
{
var prop = destProperties.FirstOrDefault(x => x.Name == sourceProperty.Name);
prop.SetValue(destination, sourceProperty.GetValue(source));
}
}
}
I want to address a specific point in your question, regarding "forgetting some properties and disaster happens". The reason this happens is that you do not have a constructor on your model, you just have setters that can be set (or not) from anywhere. This is not a good approach for defensive coding.
I use constructors on all my Models like so:
public User(Person person, string email, string username, string password, bool isActive)
{
Person = person;
Email = email;
Username = username;
Password = password;
IsActive = isActive;
}
public Person Person { get; }
public string Email { get; }
public string Username { get; }
public string Password { get; }
public bool IsActive { get; }
As you can see I have no setters, so object construction must be done via constructor. If you try to create an object without all the required parameters the compiler will complain.
With this approach it becomes clear, that tools like AutoMapper don't make sense when going from ViewModel to Model, as Model construction using this pattern is no longer about simple mapping, its about constructing your object.
Also as your Models become more sophisticated you will find that they differ significantly from your ViewModels. ViewModels tend to be flat with simple properties like string, int, bool etc. Models on the other hand often include custom objects. You will notice in my example there is a Person object, but UserViewModel would use primitives instead like so:
public class UserViewModel
{
public int Id { get; set; }
public string LastName { get; set; }
public string FirstName { get; set; }
public string Email { get; set; }
public string Username { get; set; }
public string Password { get; set; }
public bool IsActive { get; set;}
}
So mapping from primitives to complex objects limits AutoMapper's usefulness.
My approach is always manual construction for the ViewModels to Model direction. In the other direction, Models to ViewModels, I often use a hybrid approach, I would manually map Person to FirstName, LastName, I'd but use a mapper for simple properties.
Edit: Based on the discussion below, AutoMapper is better at unflattering than I believed. Though I will refrain from recommending it one way or the other, if you do use it take advantage of features like Construction and Configuration Validation to help prevent silent failures.
Use Newtonsoft.Json to serialize viewmodel first and deserialize it to model.
First we need to Serialize the viewmodel:
var viewmodel = JsonConvert.SerializeObject(companyInfoViewModel);
Then Deserialize it to model:
var model = JsonConvert.DeserializeObject<CompanyInfo>(viewmodel);
Hence, all the data is passed from viewmodel to model easily.
One Line Code:
var company = JsonConvert.DeserializeObject<CompanyInfo>(JsonConvert.SerializeObject(companyInfoViewModel));
we've been using Automapper for sometime and we think it is great utility, thanks for creating it!
However, we have a question:
Question
"How do you configure AutoMapper to map a source property to an internal destination property?"
Background
In our layered architecture, Dto objects never leave the Data Access layer, only Domain objects are allowed to pass in and out of the Data Access layer. Thus, from a domain POV, domain objects shouldn't contain any database knowledge. However, in reality database Ids are very useful to carry around - expect the 'business-layer' developer shouldn't know about them.
Solution: add the database Ids to the domain object but market them as internal so that they aren't exposed to the 'business-layer'. Next expose the Common layer (which owns the domain objects) internals to the Data Access layer. Problem solved. Expect we can't figure out how to get Automapper (> v3.3.0) to work with our internal properties.
In, version 3.3.0 BindingFlags were exposed, which use to solve the problem.
Example
Common.Dll
public class Person
{
public Parent Father { get; set; }
internal int FatherId {get; private set; }
}
DataAccess.dll
internal class PersonDto
{
public ParentDto Father { get; set; }
public int FatherId {get; private set; }
}
In our Profile class we have CreateMap<PersonDto, Person>();
Edit 1 - Fixed a typo in the return type of Father.
Edit 2 - Added more info..
In the Common.Dll, we have Services something like this:
public class ParentService
{
public Parent GetFather(Person person)
{
return repo.Parents.FirstOrDefault(parent => parent.Id = person.Father.Id);
}
}
And in the Business.Dll we have developer's using the Services something like this:
var father = parentService.GetFather(son);
// use father separately or assign it to the son. Like so:
// son.Father = father;
The whole point is, we don't want the business developer's to have access to son.FatherId from the Businssess.Dll nor do they have access to the Dto object that created the domain object.
Thus, all the 'database' knowledge is encapsulated within in the various Common.dll Services or in the DataAccess.dll.
Thanks.
This question is answered here.
I quote the answer for your convenience:
Just set the ShouldMapProperty property of your configuration object
in the initialize method.
Here is an example using the static API, however, you should be able
to achieve the same in a similar fashion by using the non-static API.
Mapper.Initialize(i =>
{
i.ShouldMapProperty = p => p.GetMethod.IsPublic || p.GetMethod.IsAssembly;
i.CreateMap<Source, Target>();
});
This is a long one.
So, I have a model and a viewmodel that I'm updating from an AJAX request. Web API controller receives the viewmodel, which I then update the existing model using AutoMapper like below:
private User updateUser(UserViewModel entityVm)
{
User existingEntity = db.Users.Find(entityVm.Id);
db.Entry(existingEntity).Collection(x => x.UserPreferences).Load();
Mapper.Map<UserViewModel, User>(entityVm, existingEntity);
db.Entry(existingEntity).State = EntityState.Modified;
try
{
db.SaveChanges();
}
catch
{
throw new DbUpdateException();
}
return existingEntity;
}
I have automapper configured like so for the User -> UserViewModel (and back) mapping.
Mapper.CreateMap<User, UserViewModel>().ReverseMap();
(Note that explicitly setting the opposite map and omitting the ReverseMap exhibits the same behavior)
I'm having an issue with a member of the Model/ViewModel that is an ICollection of a different object:
[DataContract]
public class UserViewModel
{
...
[DataMember]
public virtual ICollection<UserPreferenceViewModel> UserPreferences { get; set; }
}
The corresponding model is like such:
public class User
{
...
public virtual ICollection<UserPreference> UserPreferences { get; set; }
}
The Problem:
Every property of the User and UserViewModel classes maps correctly, except for the ICollections of UserPreferences/UserPreferenceViewModels shown above. When these collections map from the ViewModel to the Model, rather than map properties, a new instance of a UserPreference object is created from the ViewModel, rather than update the existing object with the ViewModel properties.
Model:
public class UserPreference
{
[Key]
public int Id { get; set; }
public DateTime DateCreated { get; set; }
[ForeignKey("CreatedBy")]
public int? CreatedBy_Id { get; set; }
public User CreatedBy { get; set; }
[ForeignKey("User")]
public int User_Id { get; set; }
public User User { get; set; }
[MaxLength(50)]
public string Key { get; set; }
public string Value { get; set; }
}
And the corresponding ViewModel
public class UserPreferenceViewModel
{
[DataMember]
public int Id { get; set; }
[DataMember]
[MaxLength(50)]
public string Key { get; set; }
[DataMember]
public string Value { get; set; }
}
And automapper configuration:
Mapper.CreateMap<UserPreference, UserPreferenceViewModel>().ReverseMap();
//also tried explicitly stating map with ignore attributes like so(to no avail):
Mapper.CreateMap<UserPreferenceViewModel, UserPreference>().ForMember(dest => dest.DateCreated, opts => opts.Ignore());
When mapping a UserViewModel entity to a User, the ICollection of UserPreferenceViewModels is also mapped the User's ICollection of UserPreferences, as it should.
However, when this occurs, the individual UserPreference object's properties such as "DateCreated", "CreatedBy_Id", and "User_Id" get nulled as if a new object is created rather than the individual properties being copied.
This is further shown as evidence as when mapping a UserViewModel that has only 1 UserPreference object in the collection, when inspecting the DbContext, there are two local UserPreference objects after the map statement. One that appears to be a new object created from the ViewModel, and one that is the original from the existing model.
How can I make automapper update an existing Model's collection;s members, rather than instantiate new members from the ViewModel's collection? What am I doing wrong here?
Screenshots to demonstrate before/after Mapper.Map()
This is a limitation of AutoMapper as far as I'm aware. It's helpful to keep in mind that while the library is popularly used to map to/from view models and entities, it's a generic library for mapping any class to any other class, and as such, doesn't take into account all the eccentricities of an ORM like Entity Framework.
So, here's the explanation of what's happening. When you map a collection to another collection with AutoMapper, you are literally mapping the collection, not the values from the items in that collection to items in a similar collection. In retrospect, this makes sense because AutoMapper has no reliable and independent way to ascertain how it should line up one individual item in a collection to another: by id? which property is the id? maybe the names should match?
So, what's happening is that the original collection on your entity is entirely replaced with a brand new collection composed of brand new item instances. In many situations, this wouldn't be a problem, but when you combine that with the change tracking in Entity Framework, you've now signaled that the entire original collection should be removed and replaced with a brand new set of entities. Obviously, that's not what you want.
So, how to solve this? Well, unfortunately, it's a bit of a pain. The first step is to tell AutoMapper to ignore the collection completely when mapping:
Mapper.CreateMap<User, UserViewModel>();
Mapper.CreateMap<UserViewModel, User>()
.ForMember(dest => dest.UserPreferences, opts => opts.Ignore());
Notice that I broke this up into two maps. You don't need to ignore the collection when mapping to your view model. That won't cause any problems because EF isn't tracking that. It only matters when you're mapping back to your entity class.
But, now you're not mapping that collection at all, so how do you get the values back on to the items? Unfortunately, it's a manual process:
foreach (var pref in model.UserPreferences)
{
var existingPref = user.UserPreferences.SingleOrDefault(m => m.Id == pref.Id);
if (existingPref == null) // new item
{
user.UserPreferences.Add(Mapper.Map<UserPreference>(pref));
}
else // existing item
{
Mapper.Map(pref, existingPref);
}
}
In the meantime there exists an AutoMapper Extension for that particular problem:
cfg.AddCollectionMappers();
cfg.CreateMap<S, D>().EqualityComparison((s, d) => s.ID == d.ID);
With AutoMapper.EF6/EFCore you can also auto generate all equality comparisons. Plaese see AutoMapper.Collection AutoMapper.EF6 or AutoMapper.Collection.EFCore
According to the AutoMapper source file that handles all ICollection (among other things) and the ICollection Mapper:
The collection is cleared by a call to Clear() then added again, so as far as I can see there is no way that AutoMapper will be able to automagically do the mapping this time.
I would implement some logic to loop over the collections and AutoMapper.Map the ones that are the same
I've been trying to find a flexible way of exposing an object through a 'view'. I'm probably better off explaining by way of example.
I have an Entity Framework entity model, and a web service that can be used to query it. I am able to return the entity classes themselves, but this would include some fields I might not want to share - IDs, for examples, or *Reference properties from any associations in the entity model.
I figure what I need is a view of the data, but I don't particular want to write a view wrapper class for every return type. I'm hoping I'll be able to define an interface and somehow make use of that. For example:
interface IPersonView
{
string FirstName { get; }
string LastName { get; }
}
-
// (Web service method)
IPersonView GetPerson(int id)
{
var personEntity = [...];
return GetView<IPersonView>(personEntity);
}
However, in order to do something like this, I'd have to have my entities implement the view interfaces. I was hoping for a more flexible 'duck-typed' approach as there may be many views of an object, and I don't really to want to have to implement them all.
I've had some success building a dynamic type by reflecting the interface and copying fields and properties across, but I'm not able to cast this back to the interface type in order to get strong typing on the web service.
Just looking for some comments and advice, both would be welcome. Thanks.
You shouldn't ever really be passing entities directly out to a client, they should be used for persistance only. You should introduce DTOs/POCOs tailored to whatever data your API wants to return e.g.
public class PersonDto
{
public string FirstName { get; set; }
public string LastName { get; set; }
}
// public API method
public PersonDto GetPersonApi(int id)
{
var personEntity = // pull entity from db
return new PersonDto()
{
FirstName = personEntity.FirstName,
LastName = personEntity.LastName
};
}
This keeps a clean separation between your persistence layer & public interface. You can use a tool like AutoMapper to do the legwork in terms of mapping the data across. Just setup a mapping once e.g. in your global asax:
protected void Application_Start()
{
Mapper.CreateMap<Person, PersonDto>();
}
...
// public API method
public PersonDto GetPersonApi(int id)
{
var personEntity = // pull entity from db
return Mapper.Map<Person, PersonDto>(personEntity);
}
I typically see this done with AutoMapper or a similar tool. It makes mapping between similar classes much simpler. You still have to create the Views (which in an MVC-context would be a Model), but the most tedious part (the mapping) is taken care of for you so long as you use the same field names.
As a side note, sharing IDs and other reference data will be necessary if you want to update the data, since you'll need to know the keys in order to know which record(s) to update.