SAVEPOINT

Src/FluentAssertions/Equivalency/Execution/ObjectInfo.cs

@@ -7,12 +7,15 @@ internal class ObjectInfo : IObjectInfo
     public ObjectInfo(Comparands comparands, INode currentNode)
     {
         Type = currentNode.Type;
+        ParentType = currentNode.ParentType;    
         Path = currentNode.PathAndName;
         CompileTimeType = comparands.CompileTimeType;
         RuntimeType = comparands.RuntimeType;
     }
 
     public Type Type { get; }
+
+    public Type ParentType { get; }
 
     public string Path { get; set; }
 

Src/FluentAssertions/Equivalency/Field.cs

@@ -27,6 +27,7 @@ public Field(Type reflectedType, FieldInfo fieldInfo, INode parent)
         GetSubjectId = parent.GetSubjectId;
         Name = fieldInfo.Name;
         Type = fieldInfo.FieldType;
+        ParentType = fieldInfo.DeclaringType;
         RootIsCollection = parent.RootIsCollection;
     }
 

Src/FluentAssertions/Equivalency/INode.cs

@@ -1,9 +1,11 @@
 using System;
+using JetBrains.Annotations;
 
 namespace FluentAssertions.Equivalency;
 
 /// <summary>
-/// Represents a node in the object graph as it is expected in a structural equivalency check.
+/// Represents a node in the object graph that is being compared as part of a structural equivalency check.
+/// This can be the root object, a collection item, a dictionary element, a property or a field.
 /// </summary>
 public interface INode
 {
@@ -22,9 +24,18 @@ public interface INode
     string Name { get; set; }
 
     /// <summary>
-    /// Gets the type of this node.
+    /// Gets the type of this node, e.g. the type of the field or property, or the type of the collection item. 
     /// </summary>
     Type Type { get; }
+
+    /// <summary>
+    /// Gets the type of the parent node, e.g. the type that declares a property or field.
+    /// </summary>
+    /// <value>
+    /// Is <c>null</c> for the root object.
+    /// </value>
+    [CanBeNull]
+    Type ParentType { get; }
 
     /// <summary>
     /// Gets the path from the root object UNTIL the current node, separated by dots or index/key brackets.

Src/FluentAssertions/Equivalency/IObjectInfo.cs

@@ -1,4 +1,5 @@
 using System;
+using JetBrains.Annotations;
 
 namespace FluentAssertions.Equivalency;
 
@@ -8,9 +9,19 @@ namespace FluentAssertions.Equivalency;
 public interface IObjectInfo
 {
     /// <summary>
-    /// Gets the type of this node.
+    /// Gets the type of the object 
     /// </summary>
+    [Obsolete("Use CompileTimeType or RunTimeType instead")]
     Type Type { get; }
+
+    /// <summary>
+    /// Gets the type of the parent, e.g. the type that declares a property or field.
+    /// </summary>
+    /// <value>
+    /// Is <c>null</c> for the root object.
+    /// </value>
+    [CanBeNull]
+    Type ParentType { get; }
 
     /// <summary>
     /// Gets the full path from the root object until the current node separated by dots.

Src/FluentAssertions/Equivalency/Node.cs

@@ -1,15 +1,11 @@
 using System;
 using System.Collections;
-using System.Collections.Generic;
 using System.Linq;
 using System.Text.RegularExpressions;
 using FluentAssertions.Common;
 
 namespace FluentAssertions.Equivalency;
 
-/// <summary>
-/// Represents a node in the object graph that is being compared as part of a structural equivalency check.
-/// </summary>
 public class Node : INode
 {
     private static readonly Regex MatchFirstIndex = new(@"^\[\d+\]$");
@@ -21,6 +17,8 @@ public class Node : INode
     public GetSubjectId GetSubjectId { get; protected set; } = () => string.Empty;
 
     public Type Type { get; protected set; }
+
+    public Type ParentType { get; protected set; }
 
     public string Path
     {
@@ -82,6 +80,7 @@ public static INode From<T>(GetSubjectId getSubjectId)
             Name = string.Empty,
             Path = string.Empty,
             Type = typeof(T),
+            ParentType = null,
             RootIsCollection = IsCollection(typeof(T))
         };
     }
@@ -91,6 +90,7 @@ public static INode FromCollectionItem<T>(string index, INode parent)
         return new Node
         {
             Type = typeof(T),
+            ParentType = parent.Type,
             Name = "[" + index + "]",
             Path = parent.PathAndName,
             GetSubjectId = parent.GetSubjectId,
@@ -103,6 +103,7 @@ public static INode FromDictionaryItem<T>(object key, INode parent)
         return new Node
         {
             Type = typeof(T),
+            ParentType = parent.Type,
             Name = "[" + key + "]",
             Path = parent.PathAndName,
             GetSubjectId = parent.GetSubjectId,

Src/FluentAssertions/Equivalency/Ordering/CollectionMemberObjectInfo.cs

@@ -7,7 +7,12 @@ internal class CollectionMemberObjectInfo : IObjectInfo
     public CollectionMemberObjectInfo(IObjectInfo context)
     {
         Path = GetAdjustedPropertyPath(context.Path);
+
+#pragma warning disable CS0618
         Type = context.Type;
+#pragma warning restore CS0618
+
+        ParentType = context.ParentType;
         RuntimeType = context.RuntimeType;
         CompileTimeType = context.CompileTimeType;
     }
@@ -18,6 +23,8 @@ private static string GetAdjustedPropertyPath(string propertyPath)
     }
 
     public Type Type { get; }
+
+    public Type ParentType { get; }
 
     public string Path { get; set; }
 

Src/FluentAssertions/Equivalency/Property.cs

@@ -26,6 +26,7 @@ public Property(Type reflectedType, PropertyInfo propertyInfo, INode parent)
         DeclaringType = propertyInfo.DeclaringType;
         Name = propertyInfo.Name;
         Type = propertyInfo.PropertyType;
+        ParentType = propertyInfo.DeclaringType;
         Path = parent.PathAndName;
         GetSubjectId = parent.GetSubjectId;
         RootIsCollection = parent.RootIsCollection;
@@ -36,7 +37,7 @@ public object GetValue(object obj)
         return propertyInfo.GetValue(obj);
     }
 
-    public Type DeclaringType { get; private set; }
+    public Type DeclaringType { get; }
 
     public Type ReflectedType { get; }
 

Tests/FluentAssertions.Equivalency.Specs/ExtensibilitySpecs.cs

@@ -226,6 +226,27 @@ public void When_property_of_other_is_incompatible_with_generic_type_the_message
             .WithMessage("*Id*from expectation*System.String*System.Double*");
     }
 
+    [Fact]
+    public void Can_exclude_all_properties_of_the_parent_type()
+    {
+        // Arrange
+        var subject = new
+        {
+            Id = "foo",
+        };
+
+        var other = new
+        {
+            Id = 0.5d,
+        };
+
+        // Act
+        subject.Should().BeEquivalentTo(other,
+            o => o
+                .Using<string>(c => c.Subject.Should().Be(c.Expectation))
+                .When(si => si.ParentType != other.GetType() && si.Path == "Id"));
+    }
+
     [Fact]
     public void When_property_of_subject_is_incompatible_with_generic_type_the_message_should_include_generic_type()
     {

docs/_pages/releases.md

@@ -7,6 +7,11 @@ sidebar:
   nav: "sidebar"
 ---
 
+Unreleased
+
+### What's new
+* Adds a `ParentType` to `IObjectInfo` to help determining the parent in a call to `Using`/`When` constructs - [#2000](https://github.com/fluentassertions/fluentassertions/pull/2000)
+
 ## 6.7.0
 
 ### What's new