In my domain model I have an Entity object that looks as follows:
public class Group
{
public int idGroup { get; set; }
public string Description { get; set; }
}
I have a repository for this object:
public class GroupRepository : IGroupRepository
{
public Group LoadGroup(int idGroup)
{
//imitation of SQL data reader
Group g = new Group();
g.idGroup = Convert.ToInt32(r["idTipoGrupo"]);
g.Description = Convert.ToString(r["Descricao"]);
return g;
}
}
But now I need to get some extra information from data store about Group objects through a new function in my created repository, here are the fields I need:
public bool HasChildGroups { get; set; }
public int ChildGroupsCount { get; set; }
public bool HasDeals { get; set; }
public int DealsCount { get; set; }
These properties look to me like a "service" or "helper" properties and I don't plan to use them everywhere in my application, only few times, but I need them. The simplest thing I could think of is that I added these "service" properties to my Group object and created a method in my repository that populates them. But I consider doing this wrong, as it is the Entity and I don't need them in here. So where should I keep such "service" objects? Do I have to create a new class that inherits from Group like this:
public class GroupHelper : Group
{
public bool HasChildGroups { get; set; }
public int ChildGroupsCount { get; set; }
public bool HasDeals { get; set; }
public int DealsCount { get; set; }
}
Or should I consider using some Data Transfer Objects?
How would you solve this problem?
Any help appreciated.
The first question to ask is how the state of the proposed GroupHelper object is managed. Attributes such as HasChildGroups seems like they would be altered as a result of behaviors invoked on a Group entity. If so, then they should be first class entities in your domain model, perhaps event part of the group entity itself. If the properties are managed outside of your domain model then you can just query that data as you would any other external data source. I would have this be a standalone object, perhaps called something like GroupInfo not extending Group itself.
What seems to be the issue here is that you have query requirements that aren't in alignment with the shape of your entities. In that case you have the flexibility to decouple your read-models from your domain models. Read-models are intended to fulfill query requirements and your domain models are intended to host behavior associated with your domain.
HasChildGroups [...] look to me like a "service" or "helper" properties [...] But I consider doing this wrong, as it is the Entity and I don't need them in here.
If you concider your Group object to be a data access object and you have a separate model for, say, viewdata, you're right.
But this may also be a fat class, providing in view-specific and database-specific code. It's not plain wrong.
You could indeed create a GroupDTO class that provides the properties you require in the application but not for the data access, to separate concerns.
Related
Our application has multiple drop down lists with data that is dynamically loaded from the database.
Drop down list of colours
Drop down list of Sizes
Drop down list of makes
Drop down list of models
We called 4 different procedures:
GetColours
GetSizes
GetMakes
GetModels
Historically, we map the results from those procedures to a generic model class:
public class Lookup
{
public int Key { get; set; }
public string Key_Value { get; set; }
}
This generic model is passed through to the front end, and we set option and option value to the key and key/value properties.
We are re-writing the application using clean architecture and SOLID principles.
The question is, is it still correct to map to a generic model, or it is preferred to create a separate model for each look up (SOLID), ie,
public class colourLookup
{
public int colourId { get; set; }
public string colourName { get; set; }
}
public class makeLookup
{
public int makeId { get; set; }
public string makeName { get; set; }
}
etc
Either way you look at it, Lookup is a data model, not a business class. As long as it does one thing and one thing only, is unlikely to change in the future as requirements change, is easily testable (can be mocked), and any applicable part of the Interface Segregation Principle and Dependency Inversion Principle are observed, it's fine like it is.
If you're feeling particularly nervous, just have your colourLookup and makeLookup derive from Lookup, with no specific behavior themselves.
I pretty want to understand how to organize my code. Let's say i have this class called "Brand" which has a "Product" object:
public class Brand {
public int ID { get; set; }
public int name { get; set; }
public Product product { get; set; }
public void add(Brand brand)
{
// Database logic
}
}
And this class called product
public class Product {
public int ID { get; set; }
public int name { get; set; }
}
What i want to know is should i have a method AddProduct inside product class or should the method be on the top class "Brand". That is my confusion.
In order to make better sense of this, think about separation of concerns and single responsiblity. The answer in this post is a nice way of putting this.
Right now you have an object called Brand that contains a method Add and some properties related to being a Brand object. This means that not only is the Brand charged with managing itself, it's also charged with managing it's own interaction with the database. You are fixing to have a similar coupling between the Product and the database as well. Then what happens when you have a collection of brands, and you realize each brand should have a collection of products, and they all have Database logic strewn throughout? Then, say you notice that each Product needs a list of ingredients, so you have to add that, so the ingredients need database logic, etc. etc. You can see this gets very confusing very quickly.
So really, you should have a third class that is responsible for managing database objects, and that class will have methods to call that take your Brand and Product objects as parameters and interact with the database internally. Now you have abstracted your database logic away from your Brand and Product logic, so the Database class can do what it's built for and no more, and the Brand and Class objects can exist as defined wrappers for related data and no more. Everything is now divided so each class represents a single simple concept. Brand class exists to represent brand data. Database class exists to interact with the database.
I'm sure you get the concept and you may have seen this a thousand times already, but thinking like this will help you spot what needs to change and find much simpler, cleaner, more maintainable solutions.
The way you declared the product is using the C# Auto Property.
First of all, you should ask yourself do you need the product to be visible as public member, or you want to encapsulate the logic of setting the product.
If the answer is that you want to want the Product to be able to set outside, then there is no need to declare any additional method:
public class Brand
{
public int Id { get; set; }
public string Name { get; set; }
public IProduct Product { get; set; }
}
public static void Main(string[] args)
{
var brand = new Brand
{
Id = 1,
Name = "Name",
Product = new Product()
};
}
However, if you want to encapsulate the way you set the product then consider using either Composition or Aggregation approaches:
public class Brand
{
private int _id;
public string _name;
private readonly IProduct _product;
public Brand(IProduct product, int id, string name )
{
_product = product;
_id = id;
_name = name;
}
}
public static void Main(string[] args)
{
var brand = new Brand(new Product(), 1, "prd");
}
Note: if you still want to be able to set the product after object declaration, consider a different name for the method, like SetProduct or something with close meaning, because AddProduct means that you are dealing with the collection of Products.
I have 3 classes
public class ActivityLog
{
// The activity log affects an employee
public int EmployeeID { get; set; }
public Employee Employee { get; set; }
// The activity log affects a department
public int DepartmentID { get; set; }
public Department Department { get; set; }
}
In this example there are two different object types that could be displayed on the view, but in reality there are much more types that differ and for which it doesn't seem sensible to move it to its own inheritance model.
I would like to be able to do the below:
public class ActivityLog<T>
{
// The activity log affects an unknown type
public T ConcernedObjectID { get; set; }
public T ConcernedObject { get; set; }
}
Right now we have a lot of null checks in our view (if employee is null then use department).
Is this something that entity framework can help with somehow, or would it be best to implement a code only solution (e.g. Interfaces)?
I think you have a design problem here. The ActivityLog class tries to do too much. Its both an entry in the log for an employee and for a department. Which are completely different things. The only thing they have in common is that they can be put into an activity log.
I would either use a common interface or an abstract base class. You can then use the asp.net equivalent of data templates to visualize the data.
So something like this:
public abstract class ActivityLogEntry
{
int Id { get; }
}
public EmployeeActivityLogEntry : ActivityLogEntry
{
Employee Employee {get;}
}
public DepartmentActivityLogEntry : ActivityLogEntry
{
Department Department {get;}
}
Another thing that can help you with null checks is to make it explicit that something can be null. I use the Optional NuGet package for that. This gives you something like this
Option<Employee> Employee {get; }
public string ToString()
{
return this.Employee.Match(e => e.Name, () => "");
}
In this case you cannot directly access the Employee that is captured in the Option. Instead you have to provide a Func for what to do when there is an Employee (its not null) and for when there isn't. There are a lot more helper functions in the optional library. It makes it a lot clearer that you need to handle both cases. You can no longer be surprised by something begin null.
(Of course you should not use Option<T> for everything. Only use it on properties that can sometimes be null. Not on properties that should never be null, or you start hiding bugs from yourself).
Hello I'm writing a little C# web app using asp.net core 1.1 MVC with EF (code first)
I want to know what is the best engineering choice.
Let's assume that I have a class and I need to calculate something using one or more related properties; let's make an example:
class A
{
public virtual int Id { get; set; }
public virtual Collection<B> Bs { get; set; }
public int GetMaxB()
{
return Bs.Max( b => b.Num ); /*simple example, can be more complex */
}
}
class B
{
public virtual int Id { get; set; }
public virtual int Num { get; set; }
}
So, for GetMaxB() (let's think about a more complex function, not only one line) what is the best option?
a function in the model class
a generated (NotMapped) property in the model class
a function in controller
other
Your logic can be a part of VM, you may not want to have it mix with the Model, which should be a pure class with properties.
Depends upon situations and nature of property.
A calculated property like DiscountValue (which depend few other properties) be part of Model class.
If use of a GetMaxB() is less frequent then it can be a function in Model.
If GetMaxB() is only reason for which collection class is used in Class A, then you can think separate out provided use is not frequent.
I'm trying to perform a mapping between an EF domain object to a DTO object using the Automapper 'Project' method, but am having problems when trying to project from an interface to a concrete class. My EF domain object implements an interface that I use commonly with my lookup tables:
public interface ILookupItem
{
int Id { get; set; }
string Name { get; set; }
}
and here's an example of my domain object:
public partial class ReportType : ILookupItem
{
public int Id { get; set; }
public string Name { get; set; }
}
In my app, I'm using a DTO object which exactly matches the domain object interface:
public class LookupItemModel
{
public static void CreateMapping(IConfiguration configuration)
{
configuration.CreateMap<ILookupItem, LookupItemModel>();
}
public int Id { get; set; }
public string Name { get; set; }
}
I then perform my database query with a call such as:
return DbContext.Query<ReportType>().Project().To<LookupItemModel>();
however on this call Automapper gives an error about missing a required mapping to perform the function:
Missing map from ReportType to LookupItemModel. Create using Mapper.CreateMap<ReportType, LookupItemModel>.
I would have assumed that the mapping could be performed from the interface since all it should need to know are the properties which to pull data for (Id & Name). Am I missing something to be able to perform this projection without creating maps for each concrete implementation of my interface?
Thanks!
I asked in a comment but haven't had a response yet but I'm fairly sure this is your problem so I'm going to go ahead and make it an answer.
You're creating the mapping between ILookupItem and LookupItemModel but you aren't ever calling the method that creates the map - LookupItemModel.CreateMapping().
Before you do the mapping you need to call this method:
LookupItemModel.CreateMapping(your IConfiguration);
return DbContext.Query<ReportType>().Project().To<LookupItemModel>();
That said, instead of setting up your mapping logic inside your models, I would create an AutoMapper configuration class that sets up all your maps. Something like:
public class AutoMapperConfig {
public static CreateMaps() {
CreateLookupItemMaps();
}
public static CreateLookupItemMaps() {
Mapper.CreateMap<ILookupItem, LookupItemModel>();
}
}
Or a cleaner approach would be to use AutoMapper Profiles
And then call AutomapperConfig.CreateMaps() during your app startup and you should be good.