Added a constructor for lazy cursors to the edge.

Author: michaelstaib

src/HotChocolate/Core/src/Types.CursorPagination/Edge.cs

@@ -1,9 +1,30 @@
 using System;
+using System.Diagnostics;
+using static HotChocolate.Types.Properties.CursorResources;
 
 namespace HotChocolate.Types.Pagination;
 
+/// <summary>
+/// Represents an edge in a connection.
+/// </summary>
+/// <typeparam name="T"></typeparam>
 public class Edge<T> : IEdge
 {
+    private readonly Func<T, string>? _resolveCursor;
+    private string? _cursor;
+
+    /// <summary>
+    /// Initializes a new instance of <see cref="Edge{T}" />.
+    /// </summary>
+    /// <param name="node">
+    /// The node that the edge will wrap.
+    /// </param>
+    /// <param name="cursor">
+    /// The cursor which identifies the <paramref name="node" /> in the current data set.
+    /// </param>
+    /// <exception cref="ArgumentNullException">
+    /// <paramref name="cursor" /> is <see langword="null" /> or empty.
+    /// </exception>
     public Edge(T node, string cursor)
     {
         if (string.IsNullOrEmpty(cursor))
@@ -12,12 +33,57 @@ public Edge(T node, string cursor)
         }
 
         Node = node;
-        Cursor = cursor;
+        _cursor = cursor;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of <see cref="Edge{T}" />.
+    /// </summary>
+    /// <param name="node">
+    /// The node that the edge will wrap.
+    /// </param>
+    /// <param name="resolveCursor">
+    /// A delegate that resolves the cursor which identifies the <paramref name="node" /> in the
+    /// </param>
+    /// <exception cref="ArgumentNullException">
+    /// <paramref name="resolveCursor" /> is <see langword="null" />.
+    /// </exception>
+    public Edge(T node, Func<T, string> resolveCursor)
+    {
+        Node = node;
+        _resolveCursor = resolveCursor ??
+            throw new ArgumentNullException(nameof(resolveCursor));
     }
 
+    /// <summary>
+    /// Gets the node.
+    /// </summary>
     public T Node { get; }
 
     object? IEdge.Node => Node;
 
-    public string Cursor { get; }
-}
+    /// <summary>
+    /// Gets the cursor which identifies the <see cref="Node" /> in the current data set.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">
+    /// The edge was initialized with a cursor resolver and the resolver returned <see langword="null" />.
+    /// </exception>
+    public string Cursor
+    {
+        get
+        {
+            if (_cursor is null)
+            {
+                if (_resolveCursor is null)
+                {
+                    throw new InvalidOperationException(Edge_Cursor_CursorAndResolverNull);
+                }
+
+                _cursor = _resolveCursor(Node);
+                Debug.Assert(_cursor is not null, "The edge's cursor resolver returned null.");
+            }
+
+            return _cursor;
+        }
+    }
+}

src/HotChocolate/Core/src/Types.CursorPagination/IEdge.cs

@@ -1,5 +1,8 @@
 namespace HotChocolate.Types.Pagination;
 
+/// <summary>
+/// Represents an edge in a connection.
+/// </summary>
 public interface IEdge
 {
     /// <summary>

src/HotChocolate/Core/src/Types.CursorPagination/Properties/CursorResources.Designer.cs

@@ -42,4 +42,7 @@
   <data name="ThrowHelper_PagingHandler_NoBoundariesSet" xml:space="preserve">
     <value>You must provide a `first` or `last` value to properly paginate the `{0}`.</value>
   </data>
+  <data name="Edge_Cursor_CursorAndResolverNull" xml:space="preserve">
+    <value>The edge state is invalid and has no cursor.</value>
+  </data>
 </root>