Operator overloading is working perfect in C# code, since I am trying in the following way.
**
public class HostCode
{
public string Code { get; set; }
public string Name { get; set; }
public static bool operator ==(HostCode hc1, HostCode hc2)
{
return hc1.Code == hc2.Code;
}
public static bool operator !=(HostCode hc1, HostCode hc2)
{
return true;
}
}**
I have a clas called HostCode and it contains 2 overloading methods (one for '==' and another for '!=')
And I created a collection of Host Codes below.
**var hostCodes = new List<HostCode>()
{
new HostCode(){ Code = "1", Name = "sreekanth" },
new HostCode(){ Code = "2", Name = "sajan" },
new HostCode(){ Code = "3", Name = "mathew" },
new HostCode(){ Code = "4", Name = "sachin" }
};**
***var hc = new HostCode() { Code = "1", Name = "sreekanth" };***
***var isEq = hostCodes[1] == hc;***
when I am trying like above, the respective operator method fired in HostCode class (in this case it is '=='). So that I can write my custom logic there.
But if Iam trying with a Linq query as below, it is not firing. But in this case also Iam comparing 2 objects having same type.
**var isEqual = from obj in hostCodes where (HostCode)obj == (HostCode)hc select obj;**
Can anyone please help me to find out a way which I can compare 2 objects by Linq queries?
You can use IEqualityComparer or override equals for this purpose.
public class HostCode
{
....
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
return obj as HostCode == null ? false : (obj as HostCode).Code == Code;
}
}
And IEqualityComparer usage is when you have some equality on object and in some functions like Contain, ... you want use some specific equality:
public class EqualityComparer : IEqualityComparer<HostCode >
{
public bool Equals(HostCode x, HostCode y)
{
return y.ID == x.ID;
}
public int GetHashCode(string obj)
{
return obj.GetHashCode();
}
}
Since your question is "how should I compare them for this to work" I would answer "you should overload and use .Equals() instead of =="
And what's with your overload definition of !=?
Related
Thanks in advance. I can get required output when using var but i want to get required output by using Distinct in List<>.
InventoryDetails.cs
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
}
InventoryController.cs
[HttpGet("GetInventory")]
public IActionResult GetInventory(int id)
{
//Below code will return distinct record
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
//Below code is not doing distinct
List<InventoryDetails> inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).ToList().Distinct().ToList();
}
If i use var as return type, then i am able to get distinct records. Could some one assist it.
Please try like this it may help.
IList<InventoryDetails> inventory = _context.InventoryDetails.Where(x=>x.TempId == id).GroupBy(p => new {p.PersonalInventoryGroupId, p.PersonalInventoryBinId } )
.Select(g => g.First())
.ToList();
You need to override Equals and GetHashCode.
First, let's see the AnonymousType vs InventoryDetails
var AnonymousTypeObj1 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
var AnonymousTypeObj2 = new { PersonalInventoryGroupId = 1, PersonalInventoryBinId = 1 };
Console.WriteLine(AnonymousTypeObj1.Equals(AnonymousTypeObj2)); // True
var InventoryDetailsObj1 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
var InvertoryDetailsObj2 = new InventoryDetails { PersonalInventoryBinId = 1, PersonalInventoryGroupId = 1 };
Console.WriteLine(InventoryDetailsObj1.Equals(InvertoryDetailsObj2)); // False
You can see the Equals behave differently which make Distinct behave differently. The problem is not var you mentioned in your question but AnonoymizeType
To make Distinct works as you expect, you need to override Equals and GetHashCode
public class InventoryDetails
{
public int? PersonalInventoryGroupId { get; set; }
public int? PersonalInventoryBinId { get; set; }
public override bool Equals(object obj)
{
if (obj == null) return false;
if (obj is InventoryDetails)
{
if (PersonalInventoryGroupId == (obj as InventoryDetails).PersonalInventoryGroupId
&& PersonalInventoryBinId == (obj as InventoryDetails).PersonalInventoryBinId)
return true;
}
return false;
}
public override int GetHashCode()
{
int hash = 17;
hash = hash * 23 + PersonalInventoryBinId.GetHashCode();
hash = hash * 23 + PersonalInventoryGroupId.GetHashCode();
return hash;
}
}
Another approach would be
List<InventoryDetails> inventory = (from i in TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).AsQueryable().ToList().Distinct(new customComparer()).ToList();
public class customComparer:IEqualityComparer<InventoryDetails>
{
public bool Equals(InventoryDetails x, InventoryDetails y)
{
if (x.TempId == y.TempId && x.PersonalInventoryBinId == y.PersonalInventoryBinId
&& x.PersonalInventoryGroupId == y.PersonalInventoryGroupId)
{
return true;
}
return false;
}
public int GetHashCode(InventoryDetails obj)
{
return string.Concat(obj.PersonalInventoryBinId.ToString(),
obj.PersonalInventoryGroupId.ToString(),
obj.TempId.ToString()).GetHashCode();
}
}
As said in a comment by Ivan, you make your life difficult by calling ToList before Distinct. This prevents the SQL provider from incorporating the Distinct call into the generated SQL statement. But that leaves the question: what causes the difference?
The first query generates anonymous type instances. As per the C# specification, by default anonymous types (in C#) are equal when their properties and property values are equal (structural equality). Conversely, by default, reference types (like InventoryDetails) are equal when their reference (say memory address) is equal (reference equality or identity). They can be made equal by overriding their Equals and GetHashcode methods, as some people suggested to do.
But that's not necessary if you remove the first ToList():
var inventory = (from i in _context.TempTbl
where i.TempId == id
select new InventoryDetails
{
PersonalInventoryBinId = i.PersonalInventoryBinId,
PersonalInventoryGroupId = i.PersonalInventoryGroupId,
}).Distinct().ToList();
Now the whole statement until ToList() is an IQueryable that can be translated into SQL. The SQL is executed and the database returns a distinct result set of raw records from which EF materializes InventoryDetails objects. The C# runtime code was even never aware of duplicates!
Hello I have a list of a custom object (its really just a tuple), I'm trying to remove from one list where the same object is in another list. But I'm having difficulty doing so.
Here is the code:
public class FileNameTuple
{
public FileNameTuple(string origFileName, string newFileName)
{
OrigFileName = origFileName;
NewFileName = newFileName;
}
public string OrigFileName
{
get;
set;
}
public string NewFileName
{
get;
set;
}
}
List<FileNameTuple> fileListing = new List<FileNameTuple>();
List<FileNameTuple> failedFileListing = new List<FileNameTuple>();
//doesn't work, has compliation error
fileListing.RemoveAll(i => failedFileListing.Contains(i.OrigFileName));
Contains compares the object itself, you want to compare a property. Use Any:
fileListing
.RemoveAll(i => failedFileListing.Any(fnt => i.OrigFileName == fnt.OrigFileName));
If you want to use Contains you need to override Equals (+ GetHashCode):
public class FileNameTuple
{
//...
public override bool Equals(object obj)
{
if(object.ReferenceEquals(obj, this) return true;
FileNameTuple t2 = obj as FileNameTuple;
if(t2 == null) return false;
return OrigFileName == t2.OrigFileName;
}
public override int GetHashCode()
{
return (OrigFileName ?? "").GetHashCode();
}
}
Now you can compare FileNameTuples:
fileListing.RemoveAll(i => failedFileListing.Contains(i));
If you just want a filtered list instead of changing an existing list, you can use the Except LINQ operator.
If you can't change your class like Tim Schmelter and don't want to build a custom equality comparer, you can always use my PredicateEqualityComparer.
fileListing.Except(
failedFileListing,
new PredicateEqualityComparer((f1, f2) => f1.OriginalName == f2.OriginalName));
Trying to save selections from a CheckBoxList as a comma-separated list (string) in DB (one or more choices selected). I am using a proxy in order to save as a string because otherwise I'd have to create separate tables in the DB for a relation - the work is not worth it for this simple scenario and I was hoping that I could just convert it to a string and avoid that.
The CheckBoxList uses an enum for it's choices:
public enum Selection
{
Selection1,
Selection2,
Selection3
}
Not to be convoluted, but I use [Display(Name="Choice 1")] and an extension class to display something friendly on the UI. Not sure if I can save that string instead of just the enum, although I think if I save as enum it's not a big deal for me to "display" the friendly string on UI on some confirmation page.
This is the "Record" class that saves a string in the DB:
public virtual string MyCheckBox { get; set; }
This is the "Proxy", which is some sample I found but not directly dealing with enum, and which uses IEnumerable<string> (or should it be IEnumerable<Selection>?):
public IEnumerable<string> MyCheckBox
{
get
{
if (String.IsNullOrWhiteSpace(Record.MyCheckBox)) return new string[] { };
return Record
.MyCheckBox
.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries)
.Select(r => r.Trim())
.Where(r => !String.IsNullOrEmpty(r));
}
set
{
Record.MyCheckBox = value == null ? null : String.Join(",", value);
}
}
To save in the DB, I am trying to do this in a create class:
proxy.MyCheckBox = record.MyCheckBox; //getting error here
but am getting the error:
Cannot implicitly convert 'string' to System.Collections.Generic.IEnumerable'
I don't know, if it's possible or better, to use Parse or ToString from the API for enum values.
I know that doing something like this will store whatever I put in the ("") into the DB, so it's just a matter of figuring out how to overcome the error (or, if there is an alternative):
proxy.MyCheckBox = new[] {"foo", "bar"};
I am not good with this stuff and have just been digging and digging to come up with a solution. Any help is much appreciated.
You can accomplish this using a custom user type. The example below uses an ISet<string> on the class and stores the values as a delimited string.
[Serializable]
public class CommaDelimitedSet : IUserType
{
const string delimiter = ",";
#region IUserType Members
public new bool Equals(object x, object y)
{
if (ReferenceEquals(x, y))
{
return true;
}
var xSet = x as ISet<string>;
var ySet = y as ISet<string>;
if (xSet == null || ySet == null)
{
return false;
}
// compare set contents
return xSet.Except(ySet).Count() == 0 && ySet.Except(xSet).Count() == 0;
}
public int GetHashCode(object x)
{
return x.GetHashCode();
}
public object NullSafeGet(IDataReader rs, string[] names, object owner)
{
var outValue = NHibernateUtil.String.NullSafeGet(rs, names[0]) as string;
if (string.IsNullOrEmpty(outValue))
{
return new HashSet<string>();
}
else
{
var splitArray = outValue.Split(new[] {Delimiter}, StringSplitOptions.RemoveEmptyEntries);
return new HashSet<string>(splitArray);
}
}
public void NullSafeSet(IDbCommand cmd, object value, int index)
{
var inValue = value as ISet<string>;
object setValue = inValue == null ? null : string.Join(Delimiter, inValue);
NHibernateUtil.String.NullSafeSet(cmd, setValue, index);
}
public object DeepCopy(object value)
{
// return new ISet so that Equals can work
// see http://www.mail-archive.com/nhusers#googlegroups.com/msg11054.html
var set = value as ISet<string>;
if (set == null)
{
return null;
}
return new HashSet<string>(set);
}
public object Replace(object original, object target, object owner)
{
return original;
}
public object Assemble(object cached, object owner)
{
return DeepCopy(cached);
}
public object Disassemble(object value)
{
return DeepCopy(value);
}
public SqlType[] SqlTypes
{
get { return new[] {new SqlType(DbType.String)}; }
}
public Type ReturnedType
{
get { return typeof(ISet<string>); }
}
public bool IsMutable
{
get { return false; }
}
#endregion
}
Usage in mapping file:
Map(x => x.CheckboxValues.CustomType<CommaDelimitedSet>();
I have two unrelated classes. One is exposed as API, and the other is used internally by 3rd party API.
Entity is exposed from our API, while EntityProvider is from the 3rd party assembly.
class Entity
{
public A { get; set; }
}
class EntityProvider
{
public A { get; set; }
}
Consumers of our API will provide predicates of the form Expression <Func<Entity, bool>> and I need to modify it to Expression <Func<EntityProvider, bool>> so that I can pass the same to internal 3rd party assembly.
Please help with this conversion.
Since Expressions in .NET are immutable, the only way to do this is to rebuild the whole expression. To do this usually involves inheriting from the ExpressionVisitor class. Depending on the complexity of the expressions you have to convert this could be quite complicated.
This is a simple example of a visitor that will work with simple expressions( like x=>x.Someproperty == somevalue ). It's just an example to get you started and it's in no way finished or tested(it won't handle method calls in the expression for example)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
//Type from which to convert
public class A
{
public int Property1 { get; set; }
public int Property2 { get; set; }
}
//Type to which we want the Expression converted
public class B
{
public int Property1 { get; set; }
public int Property2 { get; set; }
}
class Program
{
static void Main(string[] args)
{
//the expression we want to convert expresion
Expression<Func<A, bool>> expA = x => x.Property1 == 6 && x.Property2 == 3;
var visitor = new ParameterTypeVisitor<A,B>(expA);
var expB = visitor.Convert();
var b = new B() { Property1 = 6, Property2 = 3 };
//try the converted expression
var result = expB.Compile().Invoke(b);
}
}
public class ParameterTypeVisitor<TFrom,TTo> : ExpressionVisitor
{
private Dictionary<string, ParameterExpression> convertedParameters;
private Expression<Func<TFrom, bool>> expression;
public ParameterTypeVisitor(Expression<Func<TFrom,bool>> expresionToConvert )
{
//for each parameter in the original expression creates a new parameter with the same name but with changed type
convertedParameters = expresionToConvert.Parameters
.ToDictionary(
x => x.Name,
x => Expression.Parameter(typeof (TTo), x.Name)
);
expression = expresionToConvert;
}
public Expression<Func<TTo,bool>> Convert()
{
return (Expression<Func<TTo, bool>>)Visit(expression);
}
//handles Properties and Fields accessors
protected override Expression VisitMember(MemberExpression node)
{
//we want to replace only the nodes of type TFrom
//so we can handle expressions of the form x=> x.Property.SubProperty
//in the expression x=> x.Property1 == 6 && x.Property2 == 3
//this replaces ^^^^^^^^^^^ ^^^^^^^^^^^
if (node.Member.DeclaringType == typeof(TFrom))
{
//gets the memberinfo from type TTo that matches the member of type TFrom
var memeberInfo = typeof (TTo).GetMember(node.Member.Name).First();
//this will actually call the VisitParameter method in this class
var newExp = Visit(node.Expression);
return Expression.MakeMemberAccess(newExp, memeberInfo);
}
else
{
return base.VisitMember(node);
}
}
// this will be called where ever we have a reference to a parameter in the expression
// for ex. in the expression x=> x.Property1 == 6 && x.Property2 == 3
// this will be called twice ^ ^
protected override Expression VisitParameter(ParameterExpression node)
{
var newParameter = convertedParameters[node.Name];
return newParameter;
}
//this will be the first Visit method to be called
//since we're converting LamdaExpressions
protected override Expression VisitLambda<T>(Expression<T> node)
{
//visit the body of the lambda, this will Traverse the ExpressionTree
//and recursively replace parts of the expression we for which we have matching Visit methods
var newExp = Visit(node.Body);
//this will create the new expression
return Expression.Lambda(newExp,convertedParameters.Select(x=>x.Value));
}
}
I have this list of type IEnumerable<MyBaseType> for which I am trying to create an extra where-clause to retrieve a specific item in the list. The specific value does only exist on subtype MyFirstType and MySecondType. Not on MyBaseType.
Is it possible to create an expression kind of...
MyList.Where(b => (b is MyFirstType || (b is MySecondType)) && b.SpecificValue == message.SpecificValue);
Above is not working since b is of type MyBaseType and SpecificValue does not exist there. Also note that I do have another subtype MyThirdType that neither has the SpecificValue.
What does work doing what I want is this...
foreach (dynamic u in MyList)
{
if (u is MyFirstType || u is MySecondType)
{
if (u.SpecificValue == message.SpecificValue)
{
//Extracted code goes here
break;
}
}
}
Anyone have an idea how to create an linq expression for the above scenario?
Maybe there is a better solution but as I see it, this could work well enough... If you don't mind performance.
Well then, start by declaring an interface:
public interface IMySpecialType
{
object SpecificValue {get; set;} //you didn't specify what type this is
//all your other relevant properties which first and second types have in common
}
Then, make MyFirstType and MySecondType derive from this interface:
public class MyFirstType : MyBaseType, IMySpecialType
{
//snipet
}
public class MyFirstType : MySecondType, IMySpecialType
{
//snipet
}
Then, filter and cast:
MyList
.Where(b => (b is MyFirstType) || (b is MySecondType))
.Cast<IMySpecialType>()
.Where(b => b.SpecificValue == message.SpecificValue);
//do something
The direct translation of your code to a Linq where clause is
string messageValue = "foo";
var result = baseList.Where(item =>
{
dynamic c = item;
if(item is MyFirstType || item is MySecondType)
{
if( c.SpecificValue == messageValue)
return true;
}
return false;
});
This will require testing the type of the class though and using dynamic - so you might as well cast item to either MyFirstType or MySecondType directly.
An alternative would be using reflection to check if the property exists, using this approach you are not dependent on the actual types of your items as long as they do have the property you are interested in:
string messageValue = "foo";
var result = baseList.Where( item =>
{
var prop = item.GetType().GetProperty("SpecificValue");
if (prop != null && prop.GetValue(item, null) == messageValue)
return true;
else return false;
});
If modifying the class hierarchy is an option you can have you MyFirstType or MySecondType implement an interface that holds the property, then you can use OfType() in your Linq query:
interface ISpecific
{
string SpecificValue { get; set; }
}
class MyFirstType : MyBase, ISpecific
{
public string SpecificValue { get; set; }
}
...
string messageValue = "foo";
var result = baseList.OfType<ISpecific>()
.Where(item => item.SpecificValue == messageValue);
A far more easy way to do that would be to create an interface to mark all your classes having this property SpecificValue. Then it's a child play :
static void Main(string[] args)
{
List<MyBaseType> MyList = new List<MyBaseType>();
ISpecificValue message = new MyFirstType();
MyList.OfType<ISpecificValue>().Where(b => b.SpecificValue == message.SpecificValue);
}
}
class MyBaseType { }
interface ISpecificValue { string SpecificValue { get; set; } }
class MyFirstType : MyBaseType, ISpecificValue
{
public string SpecificValue;
}
class MySecondType : MyBaseType, ISpecificValue
{
public string SpecificValue;
}