如何在linq中比较两个不区分大小写的复杂对象

Question

I have to list object. so i need to compare these object and get satisfied list from "datActualItem" to the list. The list "datActualItem" items may be case sensitive but the list "datFiltItem" items all are small letter my code below.

 var datActualItem = (List<UserRoleListViewModel>)TempResult.ToList();
    var datFiltItem = ((List<UserRoleListViewModel>)usersDataSource.Data).ToList();

    var objnewm = new List<UserRoleListViewModel>();
            foreach (var item in datActualItem)
            {
                objnewm.Add(datActualItem.Where(s => s.Equals(datFiltItem)).FirstOrDefault());
            }

Note:- The array list item Firstname is "Sajith" other list is containing "sajith" so currently not checking due to this. I need to checking without case sensitive and to the add list from the "datActualItem"

Answer 1

To compare 2 lists with custom comparison strategy, you can create a class that implements IEqualityComparer<T> :

public class MyClassComparer : IEqualityComparer<UserRoleListViewModel>
{
    public bool Equals(UserRoleListViewModel x, UserRoleListViewModel y)
    {
        return x.ID == y.ID
            && x.FirstName.Equals(y.FirstName, StringComparison.CurrentCultureIgnoreCase)
            && x.LastName.Equals(y.LastName, StringComparison.CurrentCultureIgnoreCase);
         // continue to add all the properties needed in comparison
    }

    public int GetHashCode(MyClass obj)
    {
        StringComparer comparer = StringComparer.CurrentCultureIgnoreCase;

        int hash = 17;
        hash = hash * 31 + obj.ID.GetHashCode();
        hash = hash * 31 + (obj.FirstName == null ? 0 : comparer.GetHashCode(obj.FirstName));
        hash = hash * 31 + (obj.LastName == null ? 0 : comparer.GetHashCode(obj.LastName));
        // continue all fields

        return hash;
    }
}

Usage:

var list = actual.Except(expected, new MyClassComparer());

Another way would be to override equality of your own class UserRoleListViewModel but that affects everything and not just this Except method.

Answer 2

Use StringComparison.OrdinalIgnoreCase

bool equals = string.Equals("Test", "test", StringComparison.OrdinalIgnoreCase);

If you need to use this in Except method, you should create class which implements IEqualityComparer (see this page ) and use string.Equals("Test", "test", StringComparison.OrdinalIgnoreCase) in that class to compare two complex objects. Becasue Linq does not know according to what you are comparing data.

By default it checks the results of GetHashCode and Equals (implemented for any object) and the default implementation for a reference type is on the reference itself.