Develop Reference

Where to put constants for data models?

I am making ASP.NET core MVC project. In one Solution I have some assemblies - .Data, .Services, .Web. In the .Data there are the Models (for the database), DbContext, Migration etc. For the models I use DataAnnotations, but when there are some "magic" numbers like 100 (for the maximum length of the "Name" property) I prefer to use constants.
For example [MaxLength(CourseConstants.NameMaxLength)]. These constants I can use them in the ".Web" assemblie. For example when someone is making a course and I can restrict the maximum length of the name using the same constant like in the "Course" model.
So my question is - where to put the constants ? One way is in the separate class (example - "CourseConstants"). But I think that for better cohesion I should put the constants that are used for the "Course" model inside the "Course" class. And if I need them in ".Services" or in ".Web" I should call them from the Course class - example Course.NameMaxLength.
P.S. sorry if I dont follow some of the rules in this site and community, its my first question here.
CASE 1:
public class Course
{
public int Id { get; set; }
[Required]
[MaxLength(CourseConstants.NameMaxLength)]
public string Name { get; set; }
[Required]
[MaxLength(CourseConstants.DescriptionMaxlenght)]
public string Description { get; set; }
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
[Required]
public User Trainer { get; set; }
public string TrainerId { get; set; }
}
public class CourseConstants
{
public const int NameMaxLength = 100;
public const int DescriptionMaxlenght = 200;
}
CASE 2:
public class Course
{
public const string NameMaxLength = 100;
public const string DescriptionMaxlenght= 200;
public int Id { get; set; }
[Required]
[MaxLength(NameMaxLength)]
public string Name { get; set; }
[Required]
[MaxLength(DescriptionMaxlenght)]
public string Description { get; set; }
public DateTime StartDate { get; set; }
public DateTime EndDate { get; set; }
[Required]
public User Trainer { get; set; }
public string TrainerId { get; set; }
}

A common reason to separate models in a different project is that you might want to reuse them for other applications. For example you have an API and it returns some models in JSON format and you would want to use the exact same model in an application that consumes that API, since it's the same. Even better, when someone changes the class, it gets updated in your app as well.
Your question, though, relates to data models used inside the data access layer. These models should only be used in your business classes and, of course, in the DAL. They should not be reusable outside the scope of the DAL and projects that access data. If you want to make them consumable from the outside, you would map them to API models that would be different classes than EF classes.
That said, constants should be part of the DAL project, together with the EF data classes, since they should not be reused anywhere else. The only reason why you would put them somewhere else would be as an assembly to share between projects with constants like PersonNameLength or EmailLength or something like that.

Data annotations on models when there are multiple repository implementations

My DTOs are pretty simple classes.
public class PlainClass {
public int Id { get; set; }
public string Name { get; set; }
public List<PlainSubClass> SubObjects { get; set; }
}
public class PlainSubClass {
public int Id { get; set; }
public string Name { get; set; }
}
I have a repository interface, whose implementations are meant to retrieve data.
public interface IRepository
{
IEnumerable<PlainClass> PlainObjects { get; }
}
Now, I want to implement that interface in another class mocking the database and also using EF SQLite, and possibly more in the future. My mock is simple but, in trying to implement and then generate the database I'm getting an error back stating I need to designate a primary key.
Now, how should I go about doing that? Should I build out interfaces for my models and add annotations specific to each implementation? Should I -- if it's even possible -- add multiple sets of annotations to the models?

How to store two same entities in a database? Entity framework, c#

I have two entities with exactly the same properties:
public class Oil
{
public Guid Id { get; set; }
public string Title { get; set; }
public int Price { get; set; }
public int Ammount { get; set; }
}
public class Filter
{
public Guid Id { get; set; }
public string Title { get; set; }
public int Price { get; set; }
public int Ammount { get; set; }
}
Questions:
1) Can I somehow store them in one table? If so, than how?
2) Or should I implement inheritance? And what type then?
Edits:
In my case these two entities are just the same, they will not have any different properties in the future.
I implemented Table-per-Hierarchy approach, but there is another issue
(I have another type that has collections of oils and filters):
public class Warehouse
{
public Guid Id { get; set; }
public ICollection<Filter> Filters { get; set; }
public ICollection<Oil> Oils { get; set; }
}
So, when I create database, I get Warehouse_Id and Warehouse_Id1 fields in it. I don't want the Oil and Filter classes to have Warehouse property in them, how can I get just one field for Warehouse id in the db table?
If I include WarehouseId as a property in OilFilterBase class I will get 3 warehouse_id in the database table.
p.s. I also have DbSet<Oil> and DbSet<Filter> in my Context and don't have DbSet<OilFilterBase>.

It's hard to say what's best without knowing more about your requirements. What makes these two entities different? If they perform different functions and just happen to have the same properties, then it would probably be a good idea to store them in separate tables; that makes the most sense conceptually, and it would make things much easier if, say, you decided you wanted to add additional properties to one of them in the future.
On the other hand, if they're really the same at every level, it's also worth asking if you really need two different entity types to store them.
For the middle ground where the two classes serve related purposes but also differ in some ways, then yes, some form of inheritance might be a good approach -- either having one entity type derive from the other, or creating a new common base type and having both entities derive from that.
If you decide this is the best approach, then it looks like a good candidate for Table-per-Hierarchy mapping. You could restructure your code something like this:
public abstract class OilFilterBase
{
public Guid Id { get; set; }
public string Title { get; set; }
public int Price { get; set; }
public int Amount { get; set; }
}
public class Oil : OilFilterBase
{
}
public class Filter : OilFilterBase
{
}
...and then the Entity Framework will, by default, create a single table with an automatically-generated discriminator column, and store all instances of both entity types in that table.
If you decide that either of those entity types should have additional fields, then you could look at some of the other inheritance options, like Table-per-Type, that create separate but related tables for each entity type.
The first thing to do is decide how these classes fit together conceptually, and then figure out the best way to implement that in EF terms. If you can give more information about what these entities are and how they work, it'll be easier for people here to give good advice.
Response to Edits:
I think what's happening with the extra columns (Warehouse_Id and Warehouse_Id1) is this:
Because you're setting up the relationships for Oil and Filter separately, it's not comfortable assuming you want to use the base class's WarehouseId property as the foreign key -- what if you only wanted to set up that relationship for Oil and not Filter? It shouldn't be writing to the base class column in that case. So, it decides to create new properties instead.
Fortunately, you can use the [ForeignKey()] attribute (or the fluent API) to tell it what you really want, like this:
using System.ComponentModel.DataAnnotations.Schema;
public abstract class OilFilterBase
{
public Guid Id { get; set; }
public string Title { get; set; }
public int Price { get; set; }
public int Amount { get; set; }
public Guid WarehouseId { get; set; }
}
public class Oil : OilFilterBase
{
}
public class Filter : OilFilterBase
{
}
public class Warehouse
{
public Guid Id { get; set; }
[ForeignKey("WarehouseId")]
public virtual ICollection<Filter> Filters { get; set; }
[ForeignKey("WarehouseId")]
public virtual ICollection<Oil> Oils { get; set; }
}
Also, I think you'll need to include a DbSet<OilFilterBase> (in addition to DbSet<Oil> and DbSet<Filter>) in your context in order to get Table-per-Hierarchy inheritance to work -- try it and see.
Good luck!

Model and partial model, how to avoid the redundant code?

I have a model and a partial model which contains only the properties that I need to expose in JSON.
But the properties between the model and his partial model are redundant.
How can I avoid that or improve my approach?
namespace Dashboard.Models.UserModels
{
public class UserModel
{
public int id { get; set; }
public string dbName { get; set; }
public string firstname { get; set; }
public string lastname { get; set; }
public int idExternal { get; set; }
public int idInstance { get; set; }
public string login { get; set; }
public string password { get; set; }
public DateTime? dtContractStart { get; set; }
public DateTime? dtContractEnd { get; set; }
public string emailPro { get; set; }
public string emailPerso { get; set; }
public LuccaUserModel()
{
idInstance = -1;
}
// partial model for json result
// not sure is the best way or have to be here
public class PartialUserModel
{
public int id { get; set; }
public string firstname { get; set; }
public string lastname { get; set; }
public string emailPro { get; set; }
public string emailPerso { get; set; }
public DateTime? dtContractStart { get; set; }
public DateTime? dtContractEnd { get; set; }
public string url { get; set; }
}
// UserModel Methods
}
}

You can rename PartialUserModel UserModelBase class (or leave it as is... it just makes better logical sense to do so) and make UserModel to inherit from it:
public class UserModel : UserModelBase
{
...
}
Of course you'll need to remove all duplicate properties from UserModel in this case.

It's a thin line between doing a proper design and building an overkill design. Answer depends on many inputs, among which I chose to have project and model breadth most important.
In hope to have my answer clearer, I have to say I use different terminology. Data which is adopted for use in UI is usually called ViewModel. In your case, you would build UserViewModel which contains necessary subset of information.
If I'm working on a one-off project, I'll reuse model as a ViewModel. I'll do this by having helper method which removes sensitive information, loads up or cuts off data which is lazy loaded from database and does other preparation on data. All this is done with same model class.
If it's not a short term project, I look to create separate ViewModel classes which I map from model data. Then, if I'm working with mostly flat data I use AutoMapper tool to have data automatically copied, instead of writing my own mappers.
As another answer here states, you write a basic class with data you need in UI and extend it with other model data, however this is not a good approach for several reasons.
If violates separation of concerns. Project dealing with model and persistance should not know about your ViewModel
You may need to flatten data from related objects into ViewModel objects. In that case, your model objects would have fields which should not be there, or would be redundant.
You may need calculated fields and helper methods in ViewModel which would again end up in model, confusing everyone that is not updated about design.
You could want to adopt several unrelated model classes to same ViewModel class
To try and put it shortly, either reuse model class or create ViewModels. There is unfortunately no clever solution. If you find one, please post a comment as I'd like to hear about it :)

DTO shape: flat, complex/nested, or a mixture of both

I have an MVC2 n-tier application (DAL, Domain, Service, MVC web) using a DDD approach (Domain Driven Design), having a Domain Model with repositories. My service layer uses a Request/Response pattern, in which the Request and Response objects contain DTO's (Data Transfer Objects) to marshal data from one layer to the next, and the mapping is done via help from AutoMapper. My question is this: what shape should a DTO typically take? Can it have nested/complex DTO's as well or should it strictly be a flat projection? Or possibly a mixture of both? Also, what are the main reasons for having a flat DTO vs a more complex/nested DTO?
For instance, suppose I had a domain such as the following:
public class Employee
{
public string FirstName { get; set; }
public string LastName { get; set; }
public Company Company { get; set; }
}
public class Company
{
public string Name { get; set; }
public string Address { get; set; }
public string City { get; set; }
public string State { get; set; }
}
There are three different ways I've thought of modeling the Response object.
Option 1 - the DRYest option:
public class GetEmployeeResponse
{
public class EmployeeDTO { get; set; } // contains a CompanyDTO property
}
From the research I've done, it would be inappropriate for a DTO to take a similar shape as the domain object(s) as demonstrated above.
Option 2 - a flattened projection of the domain (anti-DRY):
public class GetEmployeeResponse
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string CompanyName { get; set; }
public string CompanyAddress { get; set; }
public string CompanyCity { get; set; }
public string CompanyState { get; set; }
}
This is more simple, like a DTO apparently should be, but ultimately makes for more DTOs.
Option 3 - a mixture of both:
public class GetEmployeeResponse
{
public EmployeeDTO Employee { get; set; }
public CompanyDTO Company { get; set; }
}
This allows for the code to be a little bit more dry, reusable and manageable, and doesn't expose my domain structure to the end user. The other main benefit is that other responses, like GetCompanyResponse could simply return CompanyDTO, without having to make a copy of all those properties, similar to option 2. What do you think? Which option of these (if any) have you taken and/or have worked for you? If these Request/Responses later get exposed as WCF service methods, does your answer change?

My personal preference would be to try and keep it flat as possible with only the required data being transfered. having said that I have used deeply nested DTO in the past because it made sense at the time and fitted the requirements. so I guess it comes down to "it depends". At the end of the day go with what makes sense for the application at hand. No point trying to shoe horn data into a DTO convention that doesn't fit what you are tying to achieve.