I have 2 parts on an API that share some similarities but function differently. I am currently trying to take data from a list object of People from class B and add this data to a list of People created from Class A(hopefully explained well enough?)
The People structure in the 2 classes are actually the same:
[XmlRoot(ElementName = "people")]
public class People
{
[XmlElement(ElementName = "member")]
public List<Member> Member { get; set; }
}
[XmlRoot(ElementName = "member")]
public class Member
{
[XmlElement(ElementName = "firstName")]
public string FirstName { get; set; }
[XmlElement(ElementName = "lastName")]
public string LastName { get; set; }
[XmlAttribute(AttributeName = "memberId")]
public string MemberId { get; set; }
[XmlAttribute(AttributeName = "memberNotes")]
public string Notes { get; set; }
[XmlElement(ElementName = "departed")]
public string Departed { get; set; }
[XmlElement(ElementName = "currentPosition")]
public Name CurrentPosition { get; set; }
}
In normal operation the following code sets the People list just fine:
public People PersonData { get; set; }
...
....
var results = ApiA.People;
PersonData = results.Member; //during normal operation only one entry of member is returned
However in another operation the results returns a Larger list of member objects so I am trying to add to the same list to ensure handling later on uses single method for both operations due to the same data structure, what I am trying is as follows:
if(PersonData == null)
PersonData = new API_A.People();
var results = ApiB.People; //person data here belongs to API_B.Person
foreach (var res in results)
{
if (res?.Member != null)
{
if (PersonData == null)
{
PersonData.Member.AddRange(res.People.Member.Cast<API_A.Member>());
break;
}
else
PersonData.Member.Union(res.People.Member.Cast<API_A.Member>());
}
}
No errors are returned in the ide but during operation I continually receive a NullReferenceException during the add range operation; so as I am still learning I would really appreciate understanding what I am doing wrong here?
2 problems are obvious.
If PersonData is null, you cannot access to PersonData.Member before creating the PersonData object first. So in your case it should be:
PersonData = new People();
Next problem you'll have is the casting. Even if everything is same in 2 different classes, unless there is an inheritance relation between those, you cannot cast one to another. What you should do is to map your one class to the other. Just create a mapper method somewhere else that maps your API_A.Member to API_B.Member and/or vica versa. This kind of mapping workarounds are widely used, feel safe creating this heavy looking mapping method.
Example:
API_A.Member MapBToA(API_B.Member member)
{
return new API_A.Member {
CharacterName = member.CharacterName,
...
};
}
Related
I'm new to OO design, and I wondering whether it is typical to have designs where objects contain lists of other objects. An example is below:
// Person object containing a list of phone numbers
public class Person
{
public Guid Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public List<Phone> Contacts { get; set; }
public void AddPhoneNumber(Phone phone)
{
Contacts.Add(phoneNumber);
}
}
// Phone object
public class Phone
{
public Guid Id { get; set; }
public string Name { get; set; }
public string Number { get; set; }
}
// Example code to establish an object:
Person p1 = new Person();
p1.FirstName = "John";
p1.LastName = "Smith";
p1.AddPhoneNumber(new Phone() { Number = "555957000" });
p1.AddPhoneNumber(new Phone() { Number = "555579561" });
Is there a better way to structure this that simplifies the design and allows easier access to the data? Thanks!
Yes, it is absolutely fine to have an object contains list of object. In OOPs this is called Composition, which represent strong relationship between participating class.
I wondering whether it is typical to have designs where objects
contain lists of other objects.
Absolutely, this is normal as an object can contain lists that belong to only that particular object. One of many examples is when you're traversing a binary tree or such you could have each node have their own list which identifies their children. There are many more cases in which an object should/could contain their own list.
Going back to your code, you seem to have an error because the code below states that the list will contain Phone objects.
public List<Phone> Contacts { get; set; }
but yet you're passing in a string object rather than a phone object.
public void AddPhoneNumber(string phoneNumber)
{
Contacts.Add(phoneNumber); // this code shouldnt compile
}
rather what you can do is this:
public void AddPhoneNumber(string phoneNumber)
{
Contacts.Add(new Phone() { Number = phoneNumber });
}
There's nothing wrong with your code. It's perfectly valid to have a list of objects within an object.
Though adding a string to your List of Phone objects will throw an error.
You can add a phone number like so:
Person p1 = new Person();
p1.Contacts.Add(new Phone() { Number = "555579561" });
Goal: to save ViewModel object by Entity Framework. I have UserViewModel object which has list of UnitViewModel. Then, I have a UserAdapter class which converts UserViewModel into Entity Framework User object (see Convert()below how).
Now, my question is how do I convert this list of UnitViewModel to its corresponding Entity Framework Unit list? - Do I have to get each object from DB Context by calling something like context.Units.Where(u=>myListofUnitIDs.Contains(u.UnitID))?
public class UserViewModel
{
public Guid? UserID { get; set; }
public string UserName { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string Password { get; set; }
public DateTime? CreateTime { get; set; }
public List<UnitViewModel> UserUnits { get; set; }
}
public class UnitViewModel
{
public Guid UnitID { get; set; }
public string Name { get; set; }
public int? SortIndex { get; set; }
public DateTime CreateTime { get; set; }
public bool Assigned { get; set; }
}
public class UserAdapter
{
public static User Convert(UserViewModel userView)
{
User user;
if (userView.UserID.HasValue)
{
using (var provider = new CoinsDB.UsersProvider())
{
user = provider.GetUser(userView.UserID.Value);
}
}
else
{
user = new User();
}
user.FirstName = userView.FirstName;
user.LastName = user.LastName;
user.Password = StringHelper.GetSHA1(userView.Password);
user.UserName = user.UserName;
user.CreateTime = DateTime.Now;
// Problem here :)
// user.Units = userView.UserUnits;
return user;
}
}
UPDATE: The main concern here is that I have to retrieve each Unit from database to match (or map) it with ViewModel.Unit objects, right? Can I avoid it?
For your information, this operation is called as Mapping mainly. So, you want to map your view model object to the entity object.
For this, you can either use already existed 3rd party library as AutoMapper. It will map properties by reflection which have same name. Also you can add your custom logic with After method. But, this approach has some advantages and disadvantages. Being aware of these disadvantages could help you to decide whether you must use this API or not. So, I suggest you to read some articles about advantages and disadvantages of AutoMapper especially for converting entities to other models. One of such disadvantages is that it can be problem to change the name of one property in the view model in the future, and AutoMapper will not handle this anymore and you won't get any warning about this.
foreach(var item in userView.UserUnits)
{
// get the mapped instance of UnitViewModel as Unit
var userUnit = Mapper.Map<UnitViewModel, UserUnit>(item);
user.Units.Add(userUnit);
}
So, I recommend to write your custom mappers.
For example, I have created a custom library for this and it maps objects lik this:
user.Units = userView.UserUnits
.Select(userUnitViewModel => userUnitViewModel.MapTo<UserUnit>())
.ToList();
And I am implementing these mapping functions as:
public class UserUnitMapper:
IMapToNew<UnitViewModel, UserUnit>
{
public UnitViewModel Map(UserUnit source)
{
return new UnitViewModel
{
Name = source.Name,
...
};
}
}
And then in runtime, I am detecting the types of the objects which will be used during mapping, and then call the Map method. In this way, your mappers will be seperated from your action methods. But, if you want it urgently, of course you can use this:
foreach(var item in userView.UserUnits)
{
// get the mapped instance of UnitViewModel as Unit
var userUnit= new UserUnit()
{
Name = item.Name,
...
};
user.Units.Add(userUnit);
}
I have a similar structure to the one below
Base class
public class BaseClass
{
public string Name { get; set; }
public string Address { get; set; }
public int Age { get; set; }
public Guid Guid { get; set; }
public string Hometown { get; set; }
}
Derived Class
public class DerivedClass : BaseClass
{
public List<DerivedClassDataItem> Data { get; set; }
}
Data class
public class DerivedClassDataItem
{
public string Datum1 { get; set; }
public string Datum2 { get; set; }
public string Datum3 { get; set; }
public string Datum4 { get; set; }
public int Datum5 { get; set; }
public DateTime Datum6 { get; set; }
}
What is the best practice to return specific set of info from the DerivedClass?
a potential set could be:
Name, Address, Guid and then a Data list that only contains Datum1 and Datum4
I could see anonymousTypes, Tuples or another set of class(es), all to be valid approaches.
My concern about creating new set of classs for the set returned is that the class(s) structure will be similar to the structure of the three mentioned above except it will have fewer selected members, which to me, does not sound ideal. (duplicate code and structure)
Using anonymousTypes was my initial solution to tackle this, something like
List<DerivedClass> list = new List<DerivedClass>();
var mySet = list.Select(d => new
{
Name = d.Name,
Address = d.Address,
.
.
.
.
.
Data = d.Data.Select(item => new
{
Datum1 = item.Datum1,
Datum4 = item.Datum4
})
});
but again, that was a headache for us to track through httpResponse and through out API calls.
Should I go with Tuple?
Any insights as to what is the best practice for doing this?
Edit
I am using this set of data to be a response returned by a API/GET call. I will send the set back using HttpRespose and then the framework will transform that into json
this is an actual method we have now
private void populateReturnFile()
{
var returnFileAnonymous = new
{
Vendor = this.Vendor,
OrganizationName = this.OrganizationName,
User = this.User,
Platform = this.Platform,
DictionaryType = this.DictionaryType,
UseCaseId = this.UseCaseId,
Data = this.Data.Select(d => new
{
MigrationTermId = d.MigrationTermId,
ImoLexicalCode = d.ImoLexicalCode
})
};
this.returnFile = returnFileAnonymous;
}
Then my GET will return the retunFile (this is a very simple method, i have remove irrelevant code)
[HttpGet]
public HttpResponseMessage Get(Guid migrationFileId)
{
ProblemList problemList = ProblemList.GetProblemList(migrationFileId);
return Request.CreateResponse(HttpStatusCode.OK, problemList.ReturnFile, new JsonMediaTypeFormatter());
}
If API calls is where you are using these classes, then I personally like to keep it simple and avoid complex inheritance hierarchy. Remember, simple code is good code.
I would make a separate class for each api request/response call. For very simple api calls (ajax requests for example) I like to use anonymous types, but for controllers that only handle API calls I like to create separate classes, organized in a nice folder structure.
Everyone has their "style" but as long as you strive for simplicity your code will be maintainable.
I have a simple test solution which consists of two projects (a 'business' layer and a Data Access layer) using Catel to tie the two together - works fine, no problems.
However, have been reading about how useful AutoMapper can be for helping to move data around such a setup by allowing easy population of DTO's and decided to give it a look...that's when my problems started!
I'm using Entity Framework 6.1, VS 2013 Express for Desktop and accessing a SQL Server Express 14 db - no problems with data retrieval and data displays correctly in my views.
AutoMapper was added using NuGet.
In order to use AutoMapper I've set up the following in my App.xaml.cs
private void InitializeAutomapper()
{
Mapper.CreateMap<Result, ResultDto>();
Mapper.AssertConfigurationIsValid();
}
This code is the first item called inside my 'OnStartup'.
A service in my business layer makes a call to the Data Access layer and retrieves a list of Result entites.
Subsequently, I take a single entity from this list and use that in the AutoMapper mapping call.
I'm trying to populate a resultDTO from this single entity, using the following
Result res = ResultList.First();
ResultDto resultDTO = Mapper.Map<Result, ResultDto>(res);
'res' is correctly populated with data but resultDTO is filled with the default values for the individual data types (in = 0, string = null, DateTime = {01/01/0001 00:00:00}) ie; no values are mapped from the source to the destination.
There are References in both projects to AutoMapper and AutoMapper.Net and no errors are raised - it just doesn't work as advertised...
I'm not slagging off the software, just asking what I'm doing wrong!
I realise there isn't much code to work on here but, in truth, what is posted here is pretty much all I've added to try out AutoMapper. I can see, conceptually how useful it could be - I just need to figure out how to make it happen so any help/comments gratefully received...:)
EDIT
#Andrew, as requested -
Result Class:
public partial class Result
{
public int Div { get; set; }
public System.DateTime Date { get; set; }
public string HomeTeam { get; set; }
public string AwayTeam { get; set; }
public int FTHG { get; set; }
public int FTAG { get; set; }
public string FTR { get; set; }
}
ResultDTO Class:
public class ResultDto
{
int Div { get; set; }
DateTime Date { get; set; }
string HomeTeam { get; set; }
string AwayTeam { get; set; }
int FTHG { get; set; }
int FTAG { get; set; }
string FTR { get; set; }
// Added tonight to try and get it to work
public ResultDto()
{
Div = 0;
Date = DateTime.Now;
HomeTeam = null;
AwayTeam = null;
FTHG = 0;
FTAG = 0;
FTR = null;
}
}
#stuartd, the following is used to retrieve the ResultList from which Result is obtained:
// Produce a list of DataLayer.Result entities.
var ResultList = (from x in dbContext.Results.Local
where x.HomeTeam == team.TeamName.ToString() || x.AwayTeam == team.TeamName.ToString()
orderby x.Date
select x).ToList();
Please note 'team.Teamname' is passed into the above from an external source - seems to be working fine.
So to sum up -
I produce ResultList as a list of Result entities.
Fill Result with the first entity in the list.
Try to map this Result entity to ResultDTO
Fail :(
Hope this helps!
By default, class members are declared private unless otherwise specified so the ResultDto properties aren't visible outside of the class.
public class ResultDto
{
int Div { get; set; }
....
}
needs to be
public class ResultDto
{
public int Div { get; set; }
....
}
AutoMapper can work out the type you are mapping from from the arguments provided. Try this:
ResultDto resultDTO = Mapper.Map<ResultDto>(res);
UPDATE
This is wrong, or at least won't help. We need to see the source and destination classes as mentioned in the comments.
Based off of the example located here:
Multiple ViewModels in View
Can anyone show this example without adding the individual items but by showing a datasource. So for instance if my business Logic layer has the means to pull the customer address then my two models would be CustomerInfo & CustomerLocations - doing it this way I am having trouble with the last line shown (the .Add) .. I tried removing the ToList but either way it says I have invalid arguements - my ViewModel class looks exactly like the example.
var ccus = new List<ViewModel.CustomerInfo>();
var cloc = new List<ViewModel.CustomerLocations>();
var cust = new ViewModel.Customers();
var cI1 = new Business.CustomerLogic.BLCustomerAddress();
cI1.LoadCustomerAddress(decryConcept, decryBnumber, intCustid).ToList();
ccus.Add(cI1);
In the previous example he declares the code inline
var car1 = new Car
{
Id = 1,
Name = "Passat"
};
I want to replace this piece with a call to my Business Logic
I have no reference to the BusinesLogic model in the new ViewModel I have setup per the example and perhaps this is where I need to tie the two objects together. Here is my code for that piece.
public class ViewModel
{ public class Customers
{ public IEnumerable<CustomerInfo> CInfo { get; set; }
public IEnumerable<CustomerLocations> CLoc { get; set; }
}
public class CustomerInfo
{
public int CustomerID { get; set; }
public string AccountNo { get; set; }
public bool Active { get; set; }
public string Company { get; set; }
.........
ccus is of type List<ViewModel.CustomerInfo> so the add method expects a ViewModel.CustomerInfo but you are passing in cI1 which is of type Business.CustomerLogic.BLCustomerAddress. Calling ToList() won't do anything as you are not storing the result of LoadCustomerAddress, so turning the result into a list has no affect on anything.