fix #1993 - prefer non-normalized property name

Dapper/DefaultTypeMap.cs

@@ -206,6 +206,24 @@ public SqlMapper.IMemberMap GetConstructorParameter(ConstructorInfo constructor,
                 {
                     // same again, minus underscore delta
                     name = name?.Replace("_", "");
+
+                    // match normalized column name vs actual property name
+                    foreach (var member in members)
+                    {
+                        if (string.Equals(name, selector(member), StringComparison.Ordinal))
+                        {
+                            return member;
+                        }
+                    }
+                    foreach (var member in members)
+                    {
+                        if (string.Equals(name, selector(member), StringComparison.OrdinalIgnoreCase))
+                        {
+                            return member;
+                        }
+                    }
+
+                    // match normalized column name vs normalized property name
                     foreach (var member in members)
                     {
                         if (string.Equals(name, selector(member)?.Replace("_", ""), StringComparison.Ordinal))

tests/Dapper.Tests/ConstructorTests.cs

@@ -1,5 +1,4 @@
 using System;
-using System.Data;
 using System.Linq;
 using Xunit;
 
@@ -241,6 +240,72 @@ public void CtorWithoutUnderscores()
             Assert.Equal("def", obj.LastName);
         }
 
+        [Fact]
+        public void Issue1993_PreferPropertyOverField() // https://github.com/DapperLib/Dapper/issues/1993
+        {
+            var oldValue = DefaultTypeMap.MatchNamesWithUnderscores;
+            try
+            {
+                DefaultTypeMap.MatchNamesWithUnderscores = true;
+
+                var map = new DefaultTypeMap(typeof(ShowIssue1993));
+                var first = map.GetMember("field_first");
+                Assert.NotNull(first);
+                Assert.Null(first.Field);
+                Assert.Equal(nameof(ShowIssue1993.FieldFirst), first.Property?.Name);
+
+                var last = map.GetMember("field_last");
+                Assert.NotNull(last);
+                Assert.Null(last.Field);
+                Assert.Equal(nameof(ShowIssue1993.FieldLast), last.Property?.Name);
+            }
+            finally
+            {
+                DefaultTypeMap.MatchNamesWithUnderscores = oldValue;
+            }
+        }
+
+        [Fact]
+        public void Issue1993_Query()
+        {
+            var oldValue = DefaultTypeMap.MatchNamesWithUnderscores;
+            try
+            {
+                DefaultTypeMap.MatchNamesWithUnderscores = true;
+
+                var obj = connection.QueryFirst<ShowIssue1993>("select 'abc' as field_first, 'def' as field_last");
+                Assert.Equal("abc", obj.FieldFirst);
+                Assert.Equal("def", obj.FieldLast);
+
+                Assert.Equal("abc", obj.AltFieldFirst);
+                Assert.Equal("def", obj.AltFieldLast);
+            }
+            finally
+            {
+                DefaultTypeMap.MatchNamesWithUnderscores = oldValue;
+            }
+        }
+
+        public class ShowIssue1993
+        {
+            private string _fieldFirst { get; set; } = null!; // not actually a field
+            public string FieldFirst
+            {
+                get => _fieldFirst;
+                set => _fieldFirst = AltFieldFirst = value;
+            }
+
+            public string FieldLast
+            {
+                get => _fieldLast;
+                set => _fieldLast = AltFieldLast = value;
+            }
+            private string _fieldLast { get; set; } = null!;// not actually a field
+
+            public string AltFieldFirst { get; set; } = null!;
+            public string AltFieldLast { get; set; } = null!;
+        }
+
         class Type_ParamsWithUnderscores
         {
             public string FirstName { get; }