Develop Reference

How to set autoincrement Ids in unit test

I'm facing the following scenario:
The IDs of my entities are auto incremented, so I set the setter of all of them to private, but when I want to make a unit test for my domain class I found myself needing to get and set the ID.
How do I go about setting the ID?
public WorkingTime(string name, short numberOfHours, short numberOfShortDays, int workingGroupId)
{
Name = name;
NumberOfHours = numberOfHours;
NumberOfShortDays = numberOfShortDays;
WorkingGroupId = workingGroupId;
ActivatedWorkingTimes = new List<WorkingTimeActivation>();
}
private ICollection<WorkingTimeActivation> _activatedWorkingTimes;
public int Id { get; private set; }
public string Name { get; set; }
public short NumberOfHours { get; set; }
public short NumberOfShortDays { get; set; }
public int WorkingGroupId { get; set; }
public virtual WorkingGroup WorkingGroup { get; set; }
public virtual ICollection<WorkingTimeActivation> ActivatedWorkingTimes { get => _activatedWorkingTimes; set => _activatedWorkingTimes = value; }
Test example:
var workingGroup = new WorkingGroup("WG", 3, Week.Sunday, 2);
workingGroup.AssignedWorkingTimes.Add(new WorkingTime("Winter", 8, 1, 1));
workingGroup.AssignedWorkingTimes.Add(new WorkingTime("Summer", 6, 0, 1));
Now I want to set workingGroupId
Should I use public setter instead ?

Should I use public setter instead ?
Probably not, no.
There are two alternatives to consider.
One is that, if the identifier is really private data, then the test shouldn't need to interact with it directly. We limit the scope of the test to the observable side effects in the model, so that we have the freedom to later change the private implementation details.
Another is that the test is trying to draw your attention to the fact that there are different strategies that you might use for generating the identifier, and that a different strategy might be appropriate in different contexts -- one strategy in use in production code, another for use in the test harness.
The basic pattern isolates the strategy and provides the affordances you need to control which strategy is applied. In the test, we implement the strategy contract using a test double, which allows the test to maintain deterministic control over what would otherwise be an arbitrary side effect.

It seems you are wanting to keep your entities in the domain layer "pure" by creating the private setter. This is a good thing. One way I've handled tests or the mapping of DTOs to entities is by creating an extension method that gives access to the private setter.
This method uses Marc Gravell's FastMember library:
using FastMember;
...
public static class DomainExtensions
{
private static readonly IDictionary<Type, TypeAccessor> _accessors = new Dictionary<Type, TypeAccessor>();
public static T With<T, TFieldOrProperty>(this T instance, Expression<Func<T, TFieldOrProperty>> fieldOrProperty, TFieldOrProperty value)
where T : class
{
if (instance == null)
return null;
if (!(fieldOrProperty.Body is MemberExpression member))
throw new ArgumentException($"Expression '{fieldOrProperty}' is not for a property or field.");
try
{
if (!_accessors.TryGetValue(typeof(T), out var ta))
lock (_accessors)
ta = _accessors[typeof(T)] = TypeAccessor.Create(typeof(T), true);
if (ta[instance, member.Member.Name] != null)
{
ta[instance, member.Member.Name] = value;
return instance;
}
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
}
// fallback to reflection
var fi = member.Member as FieldInfo;
fi?.SetValue(instance, value);
var pi = member.Member as PropertyInfo;
pi?.SetValue(instance, value);
return instance;
}
Then you use it like this:
workingGroup.With(wg => wg.WorkingGroupId, 2);
In this way your entity stays pure. Now you may say, "well I can now bypass the read-only nature of the entity." That's true, but the developer would have to explicitly and mindfully violate this access by calling With().
If test cases are the only place you need this access then put the With() method in the assembly with your tests. This guarantees your production code can't set the ID.

If Id needs to remain private to the class library and also needs to be tested via the testing project, in my opinion, this is the next best option when using C#:
Change the private set; to be an internal set; or create an internal method for setting the Id.
public int Id { get; internal set; }
In your class library that has the class that needs to be tested, in solution explorer, under Properties, in the AssemblyInfo.cs file, add the following line:
[assembly: InternalsVisibleTo("MyTestingAssembly")]
This will make the Internals in your class library that needs to be tested visible to the testing project only. This won't solve the issue of encapsulating Id from other code inside the class library but it will keep the internal concern of Id from being visible to other DLLs that are not testing the class library.

How to create a "pointer-like" class, easily exposing functions of member?

What I am trying to do is find the most elegant way to create a "pointer-like" class for a specific object/class type that I have in a project.
What I mean is a little confusing without an example. Take this really simple class:
public class MyClass
{
private string _name;
public string GetName() { return _name; }
public void SetName(string name) { _name = name; }
}
I want to create a second class which is like a pointer to it like this:
public class MyClassPtr
{
private MyClass _obj;
public bool IsValid = false;
public MyClassPtr(MyClass obj) { _obj = obj; IsValid = true; }
public void InvalidatePtr()
{
IsValid = false;
obj = null;
}
// SOME MAGIC HERE?
}
The challenge: The key is that I want to elegantly have MyClassPtr provide an interface to all of the public methods/members in MyClass without writing wrappers and/or accessors around each method/member.
I know that I could do this:
public class MyClassPtr
{
public string GetName() { return _obj.GetName(); }
...
}
But that's what I want to avoid. Is there some fundamental abstraction that I don't know of that I can apply to MyClassPtr to allow it to easily re-expose the methods/members in MyClass directed through _obj? I do NOT want MyClassPtr to inherit MyClass. Should MyClassPtr be a type instead, and some trick with accessors to expose the methods/members of MyClass?
Edit: More context on why I am looking for such a design through an example. Here is the overall goal. Imagine a platform that parses through data about people and when it finds information about a person, it creates an instance of Person with that information. You could get a handle to that person like:
Person person1 = platform.GetPerson(based_on_data);
Now, imagine the platform had two instances of Person that it thought were different people, but all of a sudden information came in that strongly suggested those two instances actually refer to the same person. So, the platform wants to merge the instances together in to a new object, let's call it personX.
Now, floating around in the platform someone had a copy of one of those two instances that got merged, which was person1. What I want to do is on-the-fly replace person1 with personX. Literally, I want person1==personX to be true, NOT just that they are two different objects with the same data. This is important since the platform could make a change to personX and unless the two objects are literally equal, a change to personX would not be automatically reflected in person1.
Since I can't on-the-fly replace person1 with personX I had that idea that I wouldn't give direct access to Person, instead I would give access to PersonPtr which the platform (on-the-fly) can change what Person it is pointing to. This would insurance that once person1ptr gets updated to point to personX, if a change is made in personX it will be seen in person1ptr

You could of course use something like
public class MyClassWrapper
{
MyClass _obj;
public MyClassWrapper(MyClass obj)
{
_obj = obj;
}
public void Invoke(Action<MyClass> action)
{
action(_obj);
}
public U Invoke<U>(Func<MyClass, U> func)
{
return func(_obj);
}
public void ChangeTo(MyClass obj)
{
_obj = obj;
}
}
Given your class looks like
public class MyClass
{
public string Name { get; set; }
}
Example:
var person1 = new MyClass { Name = "Instance1" };
var person2 = new MyClass { Name = "Instance2" };
var wrapper = new MyClassWrapper(person1);
wrapper.Invoke(x => x.Name += "original");
var x = wrapper.Invoke(x => x.Name); // Instance1original
wrapper.ChangeTo(person2);
var y = wrapper.Invoke(x => x.Name); // Instance2
but it has a major drawback: you can't access members directly, so you can't bind the data (to a DataTable or a Control).
It would be better to implement all members of your class also in your wrapper class. If you're afraid changes in your class will be forgotten to be implemented in your wrapper, just use an interface:
public interface IMyClass
{
string Name { get; set; }
}
public class MyClass : IMyClass
{
public string Name { get; set; }
}
public class MyClassWrapper: IMyClass
{
MyClass _obj;
public MyClassWrapper(MyClass obj)
{
_obj = obj;
}
public string Name
{
get { return _obj.Name; }
set { _obj.Name = value; }
}
}
Note that regardless which approach you use, you'll have to always keep a reference to the wrapper instance to actually change the underlying instance (using something like static aside).
Also, changing the underlying instance of such a wrapper without telling the component using it that it changed don't seem to be a good idea. Maybe your system is simple enough to get away with a wrapper; that's something you have to decide for yourself.
Maybe your wrapper should simply have an Invalid flag (and/or use an event to signal a change of the underlying object.). Once the underlying object is merged, it is set to true and each member access should throw an exception. This would force the component using the wrapper to deliberately react to changes and to reload the data from your service.
All in all, I think using such a wrapper will just clutter up your code and be error prone (just imagine adding multithreading to the mix). Think twice if you really need this wrapper.
Why not just simply ask your service for a new instance of your class everytime you use it (the service can simply use a cache)? Sure, you can't prevent that someone somewhere keeps a reference; but at least you'll keep your sanity.

C# Get property value without creating instance?

Is it possible to get value without creating an instance ?
I have this class:
public class MyClass
{
public string Name{ get{ return "David"; } }
public MyClass()
{
}
}
Now I need get the value "David", without creating instance of MyClass.

Real answer: no. It's an instance property, so you can only call it on an instance. You should either create an instance, or make the property static as shown in other answers.
See MSDN for more information about the difference between static and instance members.
Tongue-in-cheek but still correct answer:
Is it possible to get value without creating an instance ?
Yes, but only via some really horrible code which creates some IL passing in null as this (which you don't use in your property), using a DynamicMethod. Sample code:
// Jon Skeet explicitly disclaims any association with this horrible code.
// THIS CODE IS FOR FUN ONLY. USING IT WILL INCUR WAILING AND GNASHING OF TEETH.
using System;
using System.Reflection.Emit;
public class MyClass
{
public string Name { get{ return "David"; } }
}
class Test
{
static void Main()
{
var method = typeof(MyClass).GetProperty("Name").GetGetMethod();
var dynamicMethod = new DynamicMethod("Ugly", typeof(string),
Type.EmptyTypes);
var generator = dynamicMethod.GetILGenerator();
generator.Emit(OpCodes.Ldnull);
generator.Emit(OpCodes.Call, method);
generator.Emit(OpCodes.Ret);
var ugly = (Func<string>) dynamicMethod.CreateDelegate(
typeof(Func<string>));
Console.WriteLine(ugly());
}
}
Please don't do this. Ever. It's ghastly. It should be trampled on, cut up into little bits, set on fire, then cut up again. Fun though, isn't it? ;)
This works because it's using call instead of callvirt. Normally the C# compiler would use a callvirt call even if it's not calling a virtual member because that gets null reference checking "for free" (as far as the IL stream is concerned). A non-virtual call like this doesn't check for nullity first, it just invokes the member. If you checked this within the property call, you'd find it's null.
EDIT: As noted by Chris Sinclair, you can do it more simply using an open delegate instance:
var method = typeof(MyClass).GetProperty("Name").GetGetMethod();
var openDelegate = (Func<MyClass, string>) Delegate.CreateDelegate
(typeof(Func<MyClass, string>), method);
Console.WriteLine(openDelegate(null));
(But again, please don't!)

You can make that property static
public static string Name{ get{ return "David"; } }
Usage:
MyClass.Name;

You requirements do seem strange, but I think you're looking for some kind of metadata. You can use an attribute to achieve this:
public class NameAttribute : Attribute {
public string Name { get; private set; }
public NameAttribute(string name) {
Name = name;
}
}
[Name("George")]
public class Dad {
public string Name {
get {
return NameGetter.For(this.GetType());
}
}
}
[Name("Frank")]
public class Son : Dad {
}
public static class NameGetter {
public static string For<T>() {
return For(typeof(T));
}
public static string For(Type type) {
// add error checking ...
return ((NameAttribute)type.GetCustomAttributes(typeof(NameAttribute), false)[0]).Name;
}
}
Now this code can get names with and without instances:
Console.WriteLine(new Dad().Name);
Console.WriteLine(new Son().Name);
Console.WriteLine(NameGetter.For<Dad>());
Console.WriteLine(NameGetter.For<Son>());

You can make your property static, as pointed out by many others.
public static string Name{ get{ return "David"; } }
Be aware that this means your instances of MyClass will no longer have their own Name property, since static members belong to the class, not the individual object instances of it.
Edit:
In a note, you mentioned that you want to override the Name property in subclasses. At the same time, you want to be able to access it at the class level (access it without creating an instance of your class).
For the static properties, you would simply create a new Name property in each class. Since they are static, you're always (almost always, yay reflection) going to access them using a specific class, so you'd be specifying which version of Name you want to get. If you want to try and hack polymorphism in there and get the name from any given subclass of MyClass, you could do so using reflection, but I wouldn't recommend doing so.
Using the example from your comment:
public class Dad
{
public static string Name { get { return "George"; }
}
public class Son : Dad
{
public static string Name { get{ return "Frank"; }
}
public static void Test()
{
Console.WriteLine(Dad.Name); // prints "George"
Console.WriteLine(Son.Name); // prints "Frank"
Dad actuallyASon = new Son();
PropertyInfo nameProp = actuallyASon.GetType().GetProperty("Name");
Console.WriteLine(nameProp.GetValue(actuallyASon, null)); // prints "Frank"
}
As a side note, since you are declaring a property that has only a getter and it is returning a constant value, I recommend possibly using a const or static readonly variable instead.
public const string Name = "David";
public static readonly string Name = "David";
Usage for both would be the same:
string name = MyClass.Name;
The main benefit (and drawback) of const is that all references to it are actually replaced by its value when the code is compiled. That means it will be a little faster, but if you ever change its value, you will need to recompile ALL code that references it.

Whenever you write C# code, always check if your method and property getter/setter code does anything at all with other instance members of the class. If they don't, be sure to apply the static keyword. Certainly the case here, it trivially solves your problem.
The reason I really post to this question is that there's a bit of language bias at work in some of the answers. The C# rule that you can't call an instance method on a null object is a specific C# language rule. It is without a doubt a very wise one, it really helps to troubleshoot NullReferenceExceptions, they are raised at the call site instead of somewhere inside of a method where it gets very hard to diagnose that the this reference is null.
But this is certainly not a requirement to the CLR, nor of every language that run on the CLR. In fact, even C# doesn't enforce it consistently, you can readily bypass it in an extension method:
public static class Extensions {
public static bool IsNullOrEmpty(this string obj) {
return obj != null && obj.Length > 0;
}
}
...
string s = null;
bool empty = s.IsNullOrEmpty(); // Fine
And using your property from a language that doesn't have the same rule works fine as well. Like C++/CLI:
#include "stdafx.h"
using namespace System;
using namespace ClassLibrary1; // Add reference
int main(array<System::String ^> ^args)
{
MyClass^ obj = nullptr;
String^ name = obj->Name; // Fine
Console::WriteLine(name);
return 0;
}

Create a static property:
public class MyClass
{
public static string Name { get { return "David"; } }
public MyClass()
{
}
}
Get it like so:
string name1 = MyClass.Name;

That is not possible. As Name is an instance property, you can only get its value if you have an instance.
Also, note that you are not talking about a parameter, but about a property.

Create a static class or a static property, and you don't have to explicitly instantiate it.

How to make a property required in c#?

I have requirement in a custom class where I want to make one of my properties required.
How can I make the following property required?
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}

If you mean "the user must specify a value", then force it via the constructor:
public YourType(string documentType) {
DocumentType = documentType; // TODO validation; can it be null? blank?
}
public string DocumentType {get;private set;}
Now you can't create an instance without specifying the document type, and it can't be removed after that time. You could also allow the set but validate:
public YourType(string documentType) {
DocumentType = documentType;
}
private string documentType;
public string DocumentType {
get { return documentType; }
set {
// TODO: validate
documentType = value;
}
}

.NET 7 or newer
Syntax
public class MyClass
{
public required string Name { get; init; }
}
new MyClass(); // illegal
new MyClass { Name = "Me" }; // works fine
Remarks
The required properties must declare a setter (either init or set).
Access modifiers on properties or setters cannot be less visible than their containing type, as they would make impossible to initialize the class in some cases.
public class MyClass
{
internal required string Name { get; set; } // illegal
}
Documentation
Official documentation here
Feature demo here
.NET 6 or older
See this answer

If you mean you want it always to have been given a value by the client code, then your best bet is to require it as a parameter in the constructor:
class SomeClass
{
private string _documentType;
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}
public SomeClass(string documentType)
{
DocumentType = documentType;
}
}
You can do your validation – if you need it – either in the property's set accessor body or in the constructor.

With the release of .NET 7 and C# 11 in November 2022 you can now use the required modifier this way:
public class Person
{
public Person() { }
[SetsRequiredMembers]
public Person(string firstName) => FirstName = firstName;
public required string FirstName { get; init; }
public int Age { get; set; }
}
And when you don't have the required properties it will throw an error when you try to initialize an object.
For more information refer to:
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-11#required-members
https://learn.microsoft.com/en-us/dotnet/csharp/properties#init-only

Add a required attribute to the property
Required(ErrorMessage = "DocumentTypeis required.")]
public string DocumentType
{
get
{
return _documentType;
}
set
{
_documentType = value;
}
}
For custom attribute detail Click Here

I used an other solution, not exactly what you want, but worked for me fine because I declare the object first and based on specific situation I have different values. I didnt want to use the constructor because I then had to use dummy data.
My solution was to create Private Sets on the class (public get) and you can only set the values on the object by methods. For example:
public void SetObject(string mandatory, string mandatory2, string optional = "", string optional2 = "")

This one liner works in C# 9:
public record Document(string DocumentType);
new Document(); // compiler error
new Document("csv"); // correct way to construct with required parameter
This explains how it works. In the above code, Document is the name of the class or "record". That first line of code actually defines an entire class. In addition to this solution essentially making a required DocumentType property (required by an auto implemented constructor), because it uses records, there are additional implications. So this may not always be an appropriate solution, and the C# 11 required keyword will still come in handy at times. Just using record types doesn't automatically make properties required. The above code is a special syntax way of using records that essentially has this effect as well as making the property init only and causes a deconstructor to be automatically implemented.
A better example would be using an int property instead of a string since a string could still be empty. Unfortunately I don't know of any good way to do extra validation within the record to make sure the string is not empty or an int is in range, etc. You would have to go deeper down the TOP (type driven development) rabbit hole, which may not be a bad thing. You could create your own type that doesn't allow empty strings or integers outside your accepted range. Unfortunately such an approach would lead to runtime discovery of invalid input instead of compile time. There might be a better way using static analysis and metadata, but I've been away from C# for too long to know anything about that.

Constructors with the same argument type

I have a Person object with two constructors - one takes an int (personId), the other a string (logonName). I would like another constructor that takes a string (badgeNumber). I know this can't be done, but seems it might be a common situation. Is there a graceful way of handling this? I suppose this would apply to any overloaded method. Code:
public class Person
{
public Person() {}
public Person(int personId)
{
this.Load(personId);
}
public Person(string logonName)
{
this.Load(logonName);
}
public Person(string badgeNumber)
{
//load logic here...
}
...etc.

You could perhaps use factory methods instead?
public static Person fromId(int id) {
Person p = new Person();
p.Load(id);
return p;
}
public static Person fromLogonName(string logonName) {
Person p = new Person();
p.Load(logonName);
return p;
}
public static Person fromBadgeNumber(string badgeNumber) {
Person p = new Person();
// load logic
return p;
}
private Person() {}

You might consider using custom types.
For example, create LogonName and BadgeNumber classes.
Then your function declarations look like...
public Person(LogonName ln)
{
this.Load(ln.ToString());
}
public Person(BadgeNumber bn)
{
//load logic here...
}
Such a solution might give you a good place to keep the business logic that governs the format and usage of these strings.

You have four options that I can think of, three of which have already been named by others:
Go the factory route, as suggested by several others here. One disadvantage to this is that you can't have consistent naming via overloading (or else you'd have the same problem), so it's superficially less clean. Another, larger, disadvantage is that it precludes the possibility of allocating directly on the stack. Everything will be allocated on the heap if you take this approach.
Custom object wrappers. This is a good approach, and the one I would recommend if you are starting from scratch. If you have a lot of code using, e.g., badges as strings, then rewriting code may make this a non-viable option.
Add an enumeration to the method, specifying how to treat the string. This works, but requires that you rewrite all the existing calls to include the new enumeration (though you can provide a default if desired to avoid some of this).
Add a dummy parameter that is unused to distinguish between the two overloads. e.g. Tack a bool onto the method. This approach is taken by the standard library in a few places, e.g. std::nothrow is a dummy parameter for operator new. The disadvantages of this approach are that it's ugly and that it doesn't scale.
If you already have a large base of existing code, I'd recommend either adding the enumeration (possibly with a default value) or adding the dummy parameter. Neither is beautiful, but both are fairly simple to retrofit.
If you are starting from scratch, or only have a small amount of code, I'd recommend the custom object wrappers.
The factory methods would be an option if you have code which heavily uses the raw badge/logonName strings, but doesn't heavily use the Person class.

No.
You might consider a flag field (enum for readability) and then have the constructor use htat to determine what you meant.

That won't work. You might consider making a class called BadgeNumber that wraps a string in order to avoid this ambiguity.

You cannot have two different constructors/methods with the same signature, otherwise, how can the compiler determine which method to run.
As Zack said, I would consider creating an "options" class where you could actually pass the parameters contained in a custom type. This means you can pretty much pass as many parameters as you like, and do what you like with the options, just be careful you dont create a monolithic method that tries to do everything..
Either that, or vote for the factory pattern..

You could use a static factory method:
public static Person fromLogon(String logon) { return new Person(logon, null); }
public static Person fromBadge(String badge) { return new Person(null, badge); }

As has been suggested, custom types is the way to go in this case.

If you are using C# 3.0, you can use Object Initializers:
public Person()
{
}
public string Logon { get; set; }
public string Badge { get; set; }
You would call the constructor like this:
var p1 = new Person { Logon = "Steve" };
var p2 = new Person { Badge = "123" };

Only thing I can think of to handle what you're wanting to do is to have to params, one that describes the param type (an enum with LogonName, BadgeNumer, etc) and the second is the param value.

You could switch to a factory style pattern.
public class Person {
private Person() {}
public static PersonFromID(int personId)
{
Person p = new Person().
person.Load(personID);
return p;
this.Load(personId);
}
public static PersonFromID(string name)
{
Person p = new Person().
person.LoadFromName(name);
return p;
}
...
}
Or, as suggested, use custom types. You can also hack something using generics, but I wouldn't recommend it for readability.

Depending on your business constraints:
public class Person
{
public string Logon { get; set; } = "";
public string Badge { get; set; } = "";
public Person(string logon="", string badge="") {}
}
// Use as follow
Person p1 = new Person(logon:"MylogonName");
Person p2 = new Person(badge:"MyBadge");

How about ...
public Person(int personId)
{
this.Load(personId);
}
public Person(string logonName)
{
this.Load(logonName);
}
public Person(Object badgeNumber)
{
//load logic here...
}