Update ComparisonOperator logic to support comparing to object

src/System.Linq.Dynamic.Core/Extensions/TokenIdExtensions.cs

@@ -0,0 +1,16 @@
+using System.Linq.Dynamic.Core.Tokenizer;
+
+namespace System.Linq.Dynamic.Core.Extensions;
+
+internal static class TokenIdExtensions
+{
+    internal static bool IsEqualityOperator(this TokenId tokenId)
+    {
+        return tokenId is TokenId.Equal or TokenId.DoubleEqual or TokenId.ExclamationEqual or TokenId.LessGreater;
+    }
+
+    internal static bool IsComparisonOperator(this TokenId tokenId)
+    {
+        return tokenId is TokenId.Equal or TokenId.DoubleEqual or TokenId.ExclamationEqual or TokenId.LessGreater or TokenId.GreaterThan or TokenId.GreaterThanEqual or TokenId.LessThan or TokenId.LessThanEqual;
+    }
+}

src/System.Linq.Dynamic.Core/Parser/ExpressionHelper.cs

@@ -137,6 +137,8 @@ public Expression GenerateEqual(Expression left, Expression right)
     {
         OptimizeForEqualityIfPossible(ref left, ref right);
 
+        TryConvertTypes(ref left, ref right);
+
         WrapConstantExpressions(ref left, ref right);
 
         return Expression.Equal(left, right);
@@ -146,16 +148,20 @@ public Expression GenerateNotEqual(Expression left, Expression right)
     {
         OptimizeForEqualityIfPossible(ref left, ref right);
 
+        TryConvertTypes(ref left, ref right);
+
         WrapConstantExpressions(ref left, ref right);
 
         return Expression.NotEqual(left, right);
     }
 
     public Expression GenerateGreaterThan(Expression left, Expression right)
     {
+        TryConvertTypes(ref left, ref right);
+
         if (left.Type == typeof(string))
         {
-            return Expression.GreaterThan(GenerateStaticMethodCall("Compare", left, right), Expression.Constant(0));
+            return Expression.GreaterThan(GenerateStaticMethodCall(nameof(string.Compare), left, right), Expression.Constant(0));
         }
 
         if (left.Type.GetTypeInfo().IsEnum || right.Type.GetTypeInfo().IsEnum)
@@ -172,9 +178,11 @@ public Expression GenerateGreaterThan(Expression left, Expression right)
 
     public Expression GenerateGreaterThanEqual(Expression left, Expression right)
     {
+        TryConvertTypes(ref left, ref right);
+
         if (left.Type == typeof(string))
         {
-            return Expression.GreaterThanOrEqual(GenerateStaticMethodCall("Compare", left, right), Expression.Constant(0));
+            return Expression.GreaterThanOrEqual(GenerateStaticMethodCall(nameof(string.Compare), left, right), Expression.Constant(0));
         }
 
         if (left.Type.GetTypeInfo().IsEnum || right.Type.GetTypeInfo().IsEnum)
@@ -192,9 +200,11 @@ public Expression GenerateGreaterThanEqual(Expression left, Expression right)
 
     public Expression GenerateLessThan(Expression left, Expression right)
     {
+        TryConvertTypes(ref left, ref right);
+
         if (left.Type == typeof(string))
         {
-            return Expression.LessThan(GenerateStaticMethodCall("Compare", left, right), Expression.Constant(0));
+            return Expression.LessThan(GenerateStaticMethodCall(nameof(string.Compare), left, right), Expression.Constant(0));
         }
 
         if (left.Type.GetTypeInfo().IsEnum || right.Type.GetTypeInfo().IsEnum)
@@ -212,9 +222,11 @@ public Expression GenerateLessThan(Expression left, Expression right)
 
     public Expression GenerateLessThanEqual(Expression left, Expression right)
     {
+        TryConvertTypes(ref left, ref right);
+
         if (left.Type == typeof(string))
         {
-            return Expression.LessThanOrEqual(GenerateStaticMethodCall("Compare", left, right), Expression.Constant(0));
+            return Expression.LessThanOrEqual(GenerateStaticMethodCall(nameof(string.Compare), left, right), Expression.Constant(0));
         }
 
         if (left.Type.GetTypeInfo().IsEnum || right.Type.GetTypeInfo().IsEnum)
@@ -268,14 +280,14 @@ public void OptimizeForEqualityIfPossible(ref Expression left, ref Expression ri
 #endif
 
 #if !NET35
-        if (type == typeof(Guid) && Guid.TryParse(text, out Guid guid))
+        if (type == typeof(Guid) && Guid.TryParse(text, out var guid))
         {
             return Expression.Constant(guid, typeof(Guid));
         }
 #else
         try
         {
-            return Expression.Constant(new Guid(text));
+            return Expression.Constant(new Guid(text!));
         }
         catch
         {
@@ -399,7 +411,7 @@ private List<Expression> CollectExpressions(bool addSelf, Expression sourceExpre
         {
             switch (expression)
             {
-                case MemberExpression _:
+                case MemberExpression:
                     list.Add(sourceExpression);
                     break;
 
@@ -443,6 +455,26 @@ private List<Expression> CollectExpressions(bool addSelf, Expression sourceExpre
         return list;
     }
 
+    /// <summary>
+    /// If the types are different (and not null), try to convert the object type to other type.
+    /// </summary>
+    private void TryConvertTypes(ref Expression left, ref Expression right)
+    {
+        if (!_parsingConfig.ConvertObjectToSupportComparison || left.Type == right.Type || Constants.IsNull(left) || Constants.IsNull(right))
+        {
+            return;
+        }
+
+        if (left.Type == typeof(object))
+        {
+            left = Expression.Convert(left, right.Type);
+        }
+        else if (right.Type == typeof(object))
+        {
+            right = Expression.Convert(right, left.Type);
+        }
+    }
+
     private static Expression GenerateStaticMethodCall(string methodName, Expression left, Expression right)
     {
         return Expression.Call(null, GetStaticMethod(methodName, left, right), new[] { left, right });

src/System.Linq.Dynamic.Core/Parser/ExpressionParser.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Linq.Dynamic.Core.Exceptions;
+using System.Linq.Dynamic.Core.Extensions;
 using System.Linq.Dynamic.Core.Parser.SupportedMethods;
 using System.Linq.Dynamic.Core.Parser.SupportedOperands;
 using System.Linq.Dynamic.Core.Tokenizer;
@@ -475,17 +476,15 @@ private Expression ParseLogicalAndOrOperator()
     private Expression ParseComparisonOperator()
     {
         Expression left = ParseShiftOperator();
-        while (_textParser.CurrentToken.Id == TokenId.Equal || _textParser.CurrentToken.Id == TokenId.DoubleEqual ||
-               _textParser.CurrentToken.Id == TokenId.ExclamationEqual || _textParser.CurrentToken.Id == TokenId.LessGreater ||
-               _textParser.CurrentToken.Id == TokenId.GreaterThan || _textParser.CurrentToken.Id == TokenId.GreaterThanEqual ||
-               _textParser.CurrentToken.Id == TokenId.LessThan || _textParser.CurrentToken.Id == TokenId.LessThanEqual)
+        while (_textParser.CurrentToken.Id.IsComparisonOperator())
         {
             ConstantExpression? constantExpr;
             TypeConverter typeConverter;
             Token op = _textParser.CurrentToken;
             _textParser.NextToken();
             Expression right = ParseShiftOperator();
-            bool isEquality = op.Id == TokenId.Equal || op.Id == TokenId.DoubleEqual || op.Id == TokenId.ExclamationEqual || op.Id == TokenId.LessGreater;
+
+            var isEquality = op.Id.IsEqualityOperator();
 
             if (isEquality && (!left.Type.GetTypeInfo().IsValueType && !right.Type.GetTypeInfo().IsValueType || left.Type == typeof(Guid) && right.Type == typeof(Guid)))
             {

src/System.Linq.Dynamic.Core/ParsingConfig.cs

@@ -240,4 +240,37 @@ public IQueryableAnalyzer QueryableAnalyzer
     /// Caches constant expressions to enhance performance. Periodic cleanup is performed to manage cache size, governed by this configuration.
     /// </summary>
     public CacheConfig? ConstantExpressionCacheConfig { get; set; }
+
+    /// <summary>
+    /// Converts typeof(object) to the correct type to allow comparison (Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan and LessThanEqual).
+    ///
+    /// Default value is <c>false</c>.
+    ///
+    /// When set to <c>true</c>, the following code will work correct:
+    /// <example>
+    /// <code>
+    /// <![CDATA[
+    /// class Person
+    /// {
+    ///     public string Name { get; set; }
+    ///     public object Age { get; set; }
+    /// }
+    ///
+    /// var persons = new[]
+    /// {
+    ///     new Person { Name = "Foo", Age = 99 },
+    ///     new Person { Name = "Bar", Age = 33 }
+    /// }.AsQueryable();
+    ///
+    /// var config = new ParsingConfig
+    /// {
+    ///     ConvertObjectToSupportComparison = true
+    /// };
+    /// 
+    /// var results = persons.Where(config, "Age > 50").ToList();
+    /// ]]>
+    /// </code>
+    /// </example>
+    /// </summary>
+    public bool ConvertObjectToSupportComparison { get; set; }
 }

test/System.Linq.Dynamic.Core.Tests/Helpers/Models/User.cs

@@ -28,7 +28,7 @@ public class User
 
     public char C { get; set; }
 
-    public UserProfile Profile { get; set; }
+    public UserProfile? Profile { get; set; }
 
     public UserState State { get; set; }