How is the comparison of records and objects within the database carried out?

In databases, comparison of records and objects usually occurs based on the values of their fields, not by references or memory addresses. In C#, when working with objects that represent database records, comparison can be implemented by overriding the Equals and GetHashCode methods.

For example, if you have a class representing a record, you can define that two objects are equal if the values of key fields match:

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }

    public override bool Equals(object obj)
    {
        if (obj is Person other)
        {
            return this.Id == other.Id;
        }
        return false;
    }

    public override int GetHashCode()
    {
        return Id.GetHashCode();
    }
}

In the context of a database, record comparison usually occurs at the SQL query level, where column values are compared. ORM (e.g., Entity Framework) uses these methods for correct comparison of objects in memory.