I'm having troubles with the Except() method.
Instead of returning the difference, it returns the original set.
I've tried implementing the IEquatable and IEqualityComparer in the Account class.
I've also tried creating a separate IEqualityComparer class for Account.
When the Except() method is called from main, it doesn't seem to call my custom Equals() method, but when I tried Count(), it did call the custom GetHashCode() method!
I'm sure I made a trivial mistake somewhere and I hope a fresh pair of eyes can help me.
main:
IEnumerable<Account> everyPartnerID =
from partner in dataContext.Partners
select new Account { IDPartner = partner.ID, Name = partner.Name };
IEnumerable<Account> hasAccountPartnerID =
from partner in dataContext.Partners
from account in dataContext.Accounts
where
!partner.ID.Equals(Guid.Empty) &&
account.IDPartner.Equals(partner.ID) &&
account.Username.Equals("Special")
select new Account { IDPartner = partner.ID, Name = partner.Name };
IEnumerable<Account> noAccountPartnerID =
everyPartnerID.Except(
hasAccountPartnerID,
new LambdaComparer<Account>((x, y) => x.IDPartner.Equals(y.IDPartner)));
Account:
public class Account : IEquatable<Account>
{
public Guid IDPartner{ get; set; }
public string Name{ get; set; }
/* #region IEquatable<Account> Members
public bool Equals(Account other)
{
return this.IDPartner.Equals(other.IDPartner);
}
#endregion*/
}
LambdaComparer:
public class LambdaComparer<T> : IEqualityComparer<T>
{
private readonly Func<T, T, bool> _lambdaComparer;
private readonly Func<T, int> _lambdaHash;
public LambdaComparer(Func<T, T, bool> lambdaComparer) :
this(lambdaComparer, o => o.GetHashCode())
{
}
public LambdaComparer(Func<T, T, bool> lambdaComparer, Func<T, int> lambdaHash)
{
if (lambdaComparer == null)
throw new ArgumentNullException("lambdaComparer");
if (lambdaHash == null)
throw new ArgumentNullException("lambdaHash");
_lambdaComparer = lambdaComparer;
_lambdaHash = lambdaHash;
}
public bool Equals(T x, T y)
{
return _lambdaComparer(x, y);
}
public int GetHashCode(T obj)
{
return _lambdaHash(obj);
}
}
Basically your LambdaComparer class is broken when you pass in just a single function, because it uses the "identity hash code" provider if you don't provide anything else. The hash code is used by Except, and that's what's causing the problem.
Three options here:
Implement your own ExceptBy method and then preferably contribute it to MoreLINQ which contains that sort of thing.
Use a different implementation of IEqualityComparer<T>. I have a ProjectionEqualityComparer class you can use in MiscUtil - or you can use the code as posted in another question.
Pass a lambda expression into your LambdaComparer code to use for the hash:
new LambdaComparer<Account>((x, y) => x.IDPartner.Equals(y.IDPartner)),
x => x.IDPartner.GetHashCode());
You could also quickly fix your LambdaComparer to work when only the equality parameters are supplied like this:
public LambdaComparer(Func<T, T, bool> lambdaComparer) :
this(lambdaComparer, o => 1)
{
}
Look here, how to use and implementing IEqualityComparer in way with linq.Except and beyond.
https://www.dreamincode.net/forums/topic/352582-linq-by-example-3-methods-using-iequalitycomparer/
public class Department {
public string Code { get; set; }
public string Name { get; set; }
}
public class DepartmentComparer : IEqualityComparer {
// equal if their Codes are equal
public bool Equals(Department x, Department y) {
// reference the same objects?
if (Object.ReferenceEquals(x, y)) return true;
// is either null?
if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
return false;
return x.Code == y.Code;
}
public int GetHashCode(Department dept) {
// If Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
// if null default to 0
if (Object.ReferenceEquals(dept, null)) return 0;
return dept.Code.GetHashCode();
}
}
IEnumerable<Department> deptExcept = departments.Except(departments2,
new DepartmentComparer());
foreach (Department dept in deptExcept) {
Console.WriteLine("{0} {1}", dept.Code, dept.Name);
}
// departments not in departments2: AC, Accounts.
IMO, this answer above is the simplest solution compared to other solutions for this problem. I tweaked it such that I use the same logic for the Object class's Equals() and GetHasCode(). The benefit is that this solution is completely transparent to the client linq expression.
public class Ericsson4GCell
{
public string CellName { get; set; }
public string OtherDependantProperty { get; set; }
public override bool Equals(Object y)
{
var rhsCell = y as Ericsson4GCell;
// reference the same objects?
if (Object.ReferenceEquals(this, rhsCell)) return true;
// is either null?
if (Object.ReferenceEquals(this, null) || Object.ReferenceEquals(rhsCell, null))
return false;
return this.CellName == rhsCell.CellName;
}
public override int GetHashCode()
{
// If Equals() returns true for a pair of objects
// then GetHashCode() must return the same value for these objects.
// if null default to 0
if (Object.ReferenceEquals(this, null)) return 0;
return this.CellName.GetHashCode();
}
}
Related
I am doing unit testing, and basically want to check that the data that 2 objects hold is the same
Assert.AreEqual(object1, object2);
Assert.IsTrue(object1.Equals(object2)); //this of course doesn't work
I am searching for the C# equivalent of assertJ
Assert.That(object1).isEqualToComparingFieldByField(object2)
You could either use records (c# 9 +) or you have to override the Equals method (if you have access and you can change the objects that you're working with).
Records example:
var point = new Point(3, 4);
var point2 = new Point(3, 4);
var test = point.Equals(point2); //this is true
public record Point(int X, int Y);
with classes:
public class Point
{
public int X { get; }
public int Y { get; }
public override bool Equals(object? obj)
{
if (obj == null)
return false;
return obj is Point point && (point.X == X && point.Y == Y);
}
public override int GetHashCode()
{
return HashCode.Combine(X, Y);
}
}
if you are not allowed to touch the implementation, then you could use serialization and compare the strings:
var obj1Str = JsonConvert.SerializeObject(object1);
var obj2Str = JsonConvert.SerializeObject(object2);
Assert.Equal(obj1Str, obj2Str);
using Newtonsoft.Json nuget
C# classes are reference equality, which means that variables are the same using the standard Equals and == if they point to the same object, you could override that behaivour, but it may break something now or in the future.
Or, you could switch to using a construct that's value equality by default, which structs as well as record classes are. If you can't (or don't want to) do that you can implement a value equals "helper" method yourself. I would not recommend overriding the Equals method or the == operator, as that can (and most likely will) lead to errors in the future instead I recommend you write your own ValueEquals method or extension method, something along the lines of
class Foo
{
public int Count {get; set;}
public string Message {get; set;}
}
public static bool ValueEquals(this Foo self, Foo other)
{
return self.Count == other.Count && self.Message == other.Message;
}
public void MyTest()
{
// Arrange and Act
...
// Assert
Assert.IsTrue(myFoo1.ValueEquals(myFoo2));
}
Depending on whether or not you can/ want to add a ValueEquals to your Foo class you can decide on doing it with an extension method or a normal method.
You could also implement a IEqualityComparer<T> like
public class FooValueEqualityComparer : IEqualityComparer<Foo>
{
public bool Equals(Foo foo1, Foo foo2)
{
return foo1.Count == foo2.Count &&
foo1.Message == foo2.Message;
}
public int GetHashCode(Foo foo)
{
return foo.GetHashCode();
}
}
// Use it
public void MyTest()
{
// Arrange and Act
...
// Assert
Assert.IsTrue(new FooEqualityComparer().Equals(myFoo1, myFoo2));
}
Or, you could write a generic ValueEquals that works for all^* classes using Reflection:
public static class ValueEqualityComparer
{
public static bool ValueEquals<T>(this T self, T other) where T : class
{
var type = self.GetType();
if (type == typeof(string))
return self.Equals(other);
var properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);
foreach (var property in properties)
{
var selfValue = property.GetValue(self);
var otherValue = property.GetValue(other);
// String is special, it's not primitive but is value equality like primitives
if (property.PropertyType.IsPrimitive || property.PropertyType == typeof(string))
{
if (!selfValue.Equals(otherValue))
return false;
}
// If the property is a List value equals each member
// Maybe find another type that allows indexing and is less restrictive
else if (typeof(IEnumerable).IsAssignableFrom(property.PropertyType))
{
var selfList = ((IEnumerable)property.GetValue(self)).Cast<object>();
var otherList = ((IEnumerable)property.GetValue(other)).Cast<object>();
try
{
// Using EquiZip from MoreLinq: https://github.com/morelinq/MoreLINQ/blob/master/MoreLinq/EquiZip.cs
foreach (var element in selfList.EquiZip(otherList, (selfItem, otherItem) => new { selfItem, otherItem }))
{
if (!ValueEquals(element.selfItem, element.otherItem))
return false;
}
}
catch (InvalidOperationException)
{
// MoreLINQ throws a InvalidOperationException if our two enumerables aren't the same length
return false;
}
}
else
{
if (!ValueEquals(selfValue, otherValue))
return false;
}
}
return true;
}
}
This implementation is by no means perfect, and should honestly only be used for UnitTests and also should be thoroughly tested itself. You can see my tests as a dotnetfiddle here
Or you could do it "dirty" and serialize the objects to a string and compare those values.
I created class with overriden Equals. The problem is that Distinct method doesn't work for my class.
class MyClass
{
public int Item1 { get; private set; }
public int Item2 { get; private set; }
public MyClass(int item1, int item2)=>(Item1,Item2)=(item1,item2);
public override bool Equals(object obj)
{
var other = obj as MyClass;
if (other == null)
{
return false;
}
return (this.Item1 == other.Item1 && this.Item2 == other.Item2);
}
}
class Program
{
static void Main(string[] args)
{
MyClass x = new MyClass(1, 0);
MyClass y = new MyClass(1, 0);
var list = new List<MyClass>();
list.Add(x);
list.Add(y);
bool b = x.Equals(y)); //True
var distincts = list.Distinct(); //Doesn't work, contains both
}
}
How can I fix that and why it doesn't use my Equals in Distinct?
Distinct docs:
Returns distinct elements from a sequence by using the default equality comparer to compare values.
Let's see what the default equality comparer does:
The Default property checks whether type T implements the System.IEquatable<T> interface and, if so, returns an EqualityComparer<T> that uses that implementation. Otherwise, it returns an EqualityComparer<T> that uses the overrides of Object.Equals and Object.GetHashCode provided by T.
So basically, to make this work, you either:
implement GetHashCode as well
implement IEquatable<T>
Call the overload of Distinct that accepts a custom equality comparer.
If I were you, I would choose the second one because you need to change the least of your code.
class MyClass: IEquatable<MyClass> {
...
public bool Equals(MyClass obj)
{
if (obj == null)
{
return false;
}
return (this.Item1 == obj.Item1 && this.Item2 == obj.Item2);
}
}
You have to override GetHashCode as well:
public override int GetHashCode()
{
return Item1; // or something
}
Distinct first compares the hashcodes, which should be computed faster than the actual Equals. Equals is only further evaulated if the hashcodes are equal for two instances.
You need to implement IEquatable<MyClass> in MyClass and provide your own implementation of GetHashCode and Equals method.
see this for more information.
class MyClass
{
public int Item1 { get; private set; }
public int Item2 { get; private set; }
public MyClass(int item1, int item2)=>(Item1,Item2)=(item1,item2);
public override bool Equals(object obj)
{
var other = obj as MyClass;
if (other == null)
{
return false;
}
return (this.Item1 == other.Item1 && this.Item2 == other.Item2);
}
public override int GetHashCode()
{
return this.Item1;
}
}
This is how the custom object is defined:
public class AccountDomain
{
public string MAILDOMAIN { get; set; }
public string ORG_NAME { get; set; }
}
This is how I am populating the List of objects:
List<AccountDomain> mainDBAccountDomain = mainDB.GetAllAccountsAndDomains();
List<AccountDomain> manageEngineAccountDomain = ManageEngine.GetAllAccountsAndDomains();
This code works fine - if I look at the locals windows I can see a List of Objects in both mainDBAccountDomain and manageEngineAccountDomain.
I'm struggling with the next bit, ideally I want a new list of type AccountDomain that contains all entries that are in mainDBAccountDomain and not ManageEngineAccountDomain
Any help greatly appreciated, even if it's just a pointer in the right direction!
I want a new list of type AccountDomain that contains all entries that are in mainDBAccountDomain and not ManageEngineAccountDomain
It's very simple with linq to objects, it's exactly what the Enumerable.Except function does:
var result = mainDBAccountDomain.Except(manageEngineAccountDomain).ToList();
You can pass a comparer to the Except function if you need something different from reference equality, or you could implement Equals and GetHashCode in AccountDomain (and optionally implement IEquatable<AccountDomain> on top of these).
See this explanation if you need more details about comparers.
Here's an example:
public class AccountDomainEqualityComparer : IEqualityComparer<AccountDomain>
{
public static readonly AccountDomainEqualityComparer Instance
= new AccountDomainEqualityComparer();
private AccountDomainEqualityComparer()
{
}
public bool Equals(AccountDomain x, AccountDomain y)
{
if (ReferenceEquals(x, y))
return true;
if (x == null || y == null)
return false;
return x.MAILDOMAIN == y.MAILDOMAIN
&& x.ORG_NAME == y.ORG_NAME;
}
public int GetHashCode(AccountDomain obj)
{
if (obj == null)
return 0;
return (obj.MAILDOMAIN ?? string.Empty).GetHashCode()
^ (397 * (obj.ORG_NAME ?? string.Empty).GetHashCode());
}
}
Then, you use it like this:
var result = mainDBAccountDomain.Except(manageEngineAccountDomain,
AccountDomainEqualityComparer.Instance)
.ToList();
I have a class that was previously being used in a HashSet. This has now been changed so that the class is now used in a SortedSet, but the equality test no longer works as it did. I believe this it uses the CompareTo function for both sorting and comparing, and this is by design.
Anyone have any ideas, other than performing my own duplicate checks?
public sealed class DatedID : IEquatable<DatedID>, IComparable
{
readonly DateTime _added;
readonly int _ID;
public DateTime Added
{
get { return _added; }
}
public int ID
{
get { return _ID; }
}
public DatedID(int id)
: this(id, DateTime.Now) {}
public DatedID(int id, DateTime added)
{
id.ThrowDefault("id");
added.ThrowDefault("added");
_ID = id;
_added = added;
}
// Compare
int IComparable.CompareTo(object obj)
{
var other = (DatedID)obj;
// Newest => oldest
return this.Added > other.Added ? -1 : this.Added < other.Added ? 1 : 0;
}
// Equals
public bool Equals(DatedID other)
{
if (other == null) return false;
return this.ID == other.ID;
}
public override bool Equals(object obj)
{
if (obj == null) return false;
var di = obj as DatedID;
return di == null ? false : Equals(di);
}
public override int GetHashCode()
{
return ID.GetHashCode();
}
}
If you mean you need to be able to handle multiple values with different IDs but the same DateTime, you could include that in your CompareTo implementation:
// TODO: Implement IComparable<DatedID> as well :)
int IComparable.CompareTo(object obj)
{
var other = (DatedID)obj;
int dateComparison = other.Added.CompareTo(this.Added);
return dateComparison != 0
? dateComparison
: _ID.CompareTo(other._ID);
}
If you mean you don't want to be able to add multiple values with the same ID but different dates, then you can't achieve that with SortedSet. In SortedSet, the only measure of equality is if the comparison returns 0.
I have defined the following interface:
public interface IHaveAProblem
{
string Issue { get; set; }
}
And here is the implementation of IHaveAProblem:
public class SomeProblem : IHaveAProblem
{
public string Issue { get; set; }
public override bool Equals(object obj)
{
SomeProblem otherObj = obj as SomeProblem;
if (otherObj == null)
{
return false;
}
return this.Issue == otherObj.Issue;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
public static bool operator ==(SomeProblem rhs, SomeProblem lhs)
{
// Null check
if (Object.ReferenceEquals(rhs, null) || Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(rhs, null) && Object.ReferenceEquals(lhs, null))
{
// Both are null. They do equal each other
return true;
}
// Only 1 is null the other is not so they do not equal
return false;
}
return rhs.Equals(lhs);
}
public static bool operator !=(SomeProblem rhs, SomeProblem lhs)
{
// Null check
if (Object.ReferenceEquals(rhs, null) || Object.ReferenceEquals(lhs, null))
{
if (Object.ReferenceEquals(rhs, null) && Object.ReferenceEquals(lhs, null))
{
// Both are null. They do equal each other
return false;
}
// Only 1 is null the other is not so they do not equal
return true;
}
return !rhs.Equals(lhs);
}
}
When I use the object, I can get the correct results for the == compare:
SomeProblem firstTest = new SomeProblem()
{
Issue = "Hello World"
};
SomeProblem secondTest = new SomeProblem()
{
Issue = "Hello World"
};
// This is true
bool result = firstTest == secondTest;
However, when I try to compare the interfaces, it is doing a memory compare rather than the operator == on SomeProblem:
IHaveAProblem firstProblem = new SomeProblem()
{
Issue = "Hello World"
};
IHaveAProblem secondProblem = new SomeProblem()
{
Issue = "Hello World"
};
Is it possible to have the interface use the == on SomeProblem rather than a memory compare?
I know I can do a firstProblem.Equals(secondProblem) and get the proper results. However, I am creating a framework and I will not know how it is used in the end. I thought == would work correctly.
The operator == is static. You cannot define static methods for interfaces in C#. Also, for all operators at least one of the argument types needs to be of the same type as the class it is defined in, therefore: No operator overloading for interfaces :(
What you CAN do is use an abstract class instead - and define the operator there. Again, the operator may NOT be virtual (since static methods cannot be virtual...)
[Edited, reason see comment.]
I konw, this is an old question, but all examples provided show how to compare two class instances, and no one points out how to compare two interface instances.
In some cases, this is the DRYest way to compare interfaces.
public interface IHaveAProblem
{
string Issue { get; set; }
}
public class IHaveAProblemComparer : IComparer<IHaveAProblem>, IEqualityComparer<IHaveAProblem>
{
public int Compare(IHaveAProblem x, IHaveAProblem y)
{
return string.Compare(x.Issue, y.Issue);
}
public bool Equals(IHaveAProblem x, IHaveAProblem y)
{
return string.Equals(x.Issue, y.Issue);
}
public int GetHashCode(IHaveAProblem obj)
{
return obj.GetHashCode();
}
}
Usage?
IHaveAProblemComparer comparer = new IHaveAProblemComparer();
List<IHaveAProblem> myListOfInterfaces = GetSomeIHaveAProblemObjects();
myListOfInterfaces.Sort(comparer); // items ordered by Issue
IHaveAProblem obj1 = new SomeProblemTypeA() { Issue = "Example1" };
IHaveAProblem obj2 = new SomeProblemTypeB() { Issue = "Example2" };
bool areEquals = comparer.Equals(obj1, obj2); // False
IIRC (and I could be wrong here), C# interfaces don't allow operator overloading.
But in this case that's okay. The == operator normally maps to reference equality. It sounds like you want value equality, and that means you want to force them to override the .Equals() (and consequently also .GetHashCode()) functions. You do that by having your interface inherit from IEquatable.
Have you tried implementing IComparable?
Like this:
public interface IHaveAProblem : IComparable
{
string Issue { get; set; }
}
And then in the implementation of the class:
public class SomeProblem : IHaveAProblem
{
public string Issue { get; set; }
...
public int CompareTo(object obj)
{
return Issue.CompareTo(((SomeProblem)obj).Issue);
}
}
Note that, this works only when you compare two instances of SomeProblem, but not any other implementations of the IHaveAProblem interface.
Not sure if there could occur a NullReferenceException.