带复合键的SortedDictionary：按1个属性建立索引，然后按另一个属性进行排序

Question

I am trying to implement a SortedDictionary as:

public IDictionary<CustomAttributeDataKey, object> Data { get; } = new SortedDictionary<CustomAttributeDataKey, object>();

I have defined CustomAttributeDataKey as:

public class CustomAttributeDataKey : IComparable {
    public long CustomAttributeID { get; set; }
    public int Order { get; set; }

    //ASSUMING this is used to check if there is a collision of keys
    protected bool Equals(CustomAttributeDataKey other) {
        return CustomAttributeID == other.CustomAttributeID;
    }

    //ASSUMING this is used to check if there is a collision of keys
    public override bool Equals(object obj) {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((CustomAttributeDataKey) obj);
    }

    //ASSUMING this is used to check if the key exists in the dictionary
    public override int GetHashCode() {
        return CustomAttributeID.GetHashCode();
    }

    //ASSUMING this is used for sorting
    public int CompareTo(object y) {
        if (y == null)
            return 0;

        return this.Order.CompareTo(((CustomAttributeDataKey) y).Order);
    }
}

Here's what I would like to happen:

1. I would like to key the dictionary on "CustomAttributeID" property ONLY
2. I would like the dictionary to sort by "Order" property when I enumerate the keys.

Whenever I add items to the dictionary I don't see any breakpoints in the "GetHashCode" or "Equals" methods being hit but I am seeing a breakpoint being hit in "CompareTo". So not sure how SortedDictionary would actually work in this case scenario. I'd be interested to find out how to make SortedDictionary work in this scenario (I know I can do this through Linq's OrderBy() method).

Answer 1

Here's what I would like to happen:

1. I would like to key the dictionary on "CustomAttributeID" property ONLY

2. I would like the dictionary to sort by "Order" property when I enumerate the keys.

Whenever I add items to the dictionary I don't see any breakpoints in the "GetHashCode" or "Equals" methods being hit but I am seeing a breakpoint being hit in "CompareTo". So not sure how SortedDictionary would actually work in this case scenario. I'd be interested to find out how to make SortedDictionary work in this scenario (I know I can do this through Linq's OrderBy() method).

Per The MSDN , SortedDictionary is stored using a binary search tree (Per The MSDN , SortedList is stored using a sorted list of Key-Value pairs) . This has a few implications which may be relevant to you:

1. SortedDictionary uses an IComparer , not GetHashCode / Equals . Equals is insufficient to gain a total ordering and similultaneously using Equals and CompareTo would be a bad idea, so Equals is not used at all.
2. Retrieval and insertion into a SortedDictionary are both O(log(n)).
3. Per The MSDN , enumerating a SortedDictionary retains the order of the dictionary. The way to control the order of the enumeration of the SortedDictionary is by ensuring that CompareTo orders the dctionary in the same way.

Personally, I would hesitate to order a SortedDictionary by an "Order" property, as sorting by such a property means you can only lookup members by their position. This provides a strong link between object position and object equality which does not normally exist. At that point, you may as well use a sorted List<T> instead.