new DbString support

Dapper/SqlMapper.cs

@@ -589,6 +589,15 @@ public static void PackListParameters(IDbCommand command, string namePrefix, obj
             
             foreach (var prop in type.GetProperties().OrderBy(p => p.Name))
             {
+                if(prop.PropertyType == typeof(DbString))
+                {
+                    il.Emit(OpCodes.Ldloc_0); // stack is now [parameters] [typed-param]
+                    il.Emit(OpCodes.Callvirt, prop.GetGetMethod()); // stack is [parameters] [dbstring]
+                    il.Emit(OpCodes.Ldarg_0); // stack is now [parameters] [dbstring] [command]
+                    il.Emit(OpCodes.Ldstr, "@" + prop.Name); // stack is now [parameters] [dbstring] [command] [name]
+                    il.EmitCall(OpCodes.Callvirt, typeof(DbString).GetMethod("AddParameter"), null); // stack is now [parameters]
+                    continue;
+                }
                 DbType dbType = LookupDbType(prop.PropertyType);
                 if (dbType == DbType.Xml)
                 {
@@ -1006,12 +1015,12 @@ void SqlMapper.IDynamicParameters.AddParameter(IDbCommand command)
                 var p = command.CreateParameter();
                 var val = param.Value;
                 p.ParameterName = param.Name;
-                p.Value = val;
+                p.Value = val ?? DBNull.Value;
                 p.Direction = param.ParameterDirection;
                 var s = val as string; 
                 if (s != null)
                 {
-                    if (s.Length < 4000)
+                    if (s.Length <= 4000)
                     {
                         p.Size = 4000;
                     }
@@ -1034,4 +1043,32 @@ public T Get<T>(string name)
             return (T)parameters[name].AttachedParam.Value;
         }
     }
+    public sealed class DbString
+    {
+        public DbString() { Length = -1; }
+        public bool IsAnsi { get; set; }
+        public bool IsFixedLength { get; set; }
+        public int Length { get; set; }
+        public string Value { get; set; }
+        public void AddParameter(IDbCommand command, string name)
+        {
+            if (IsFixedLength && Length == -1)
+            {
+                throw new InvalidOperationException("If specifying IsFixedLength,  a Length must also be specified");
+            }
+            var param = command.CreateParameter();
+            param.ParameterName = name;
+            param.Value = (object)Value ?? DBNull.Value;
+            if (Length == -1 && Value != null && Value.Length <= 4000)
+            {
+                param.Size = 4000;
+            }
+            else
+            {
+                param.Size = Length;
+            }
+            param.DbType = IsAnsi ? (IsFixedLength ? DbType.AnsiStringFixedLength : DbType.AnsiString) : (IsFixedLength ? DbType.StringFixedLength : DbType.String);
+            command.Parameters.Add(param);
+        }
+    }
 }

Tests/Tests.cs

@@ -337,6 +337,31 @@ public void TestMultiMapDynamic()
             connection.Execute("drop table #Users drop table #Posts");
         }
 
+        class Product
+        {
+            public int Id { get; set; }
+            public string Name { get; set; }
+            public Category Category { get; set; }
+        }
+        class Category
+        {
+            public int Id { get; set; }
+            public string Name { get; set; }
+        }
+        public void TestMultiMapWithSplit() // http://stackoverflow.com/q/6056778/23354
+        {
+            var sql = @"select 1 as id, 'abc' as name, 2 as id, 'def' as name";
+            var product = connection.Query<Product, Category, Product>(sql, (prod, cat) =>
+            {
+                prod.Category = cat;
+                return prod;
+            }).First();
+            // assertions
+            product.Id.IsEqualTo(1);
+            product.Name.IsEqualTo("abc");
+            product.Category.Id.IsEqualTo(2);
+            product.Category.Name.IsEqualTo("def");
+        }
         public void TestFieldsAndPrivates()
         {
             var data = connection.Query<TestFieldCaseAndPrivatesEntity>(
@@ -544,6 +569,26 @@ select 1111
 
         }
 
+        public void TestDbString()
+        {
+            var obj = connection.Query("select datalength(@a) as a, datalength(@b) as b, datalength(@c) as c, datalength(@d) as d, datalength(@e) as e, datalength(@f) as f",
+                new
+                {
+                    a = new DbString { Value = "abcde", IsFixedLength = true, Length = 10, IsAnsi = true },
+                    b = new DbString { Value = "abcde", IsFixedLength = true, Length = 10, IsAnsi = false },
+                    c = new DbString { Value = "abcde", IsFixedLength = false, Length = 10, IsAnsi = true },
+                    d = new DbString { Value = "abcde", IsFixedLength = false, Length = 10, IsAnsi = false },
+                    e = new DbString { Value = "abcde", IsAnsi = true },
+                    f = new DbString { Value = "abcde", IsAnsi = false },
+                }).First();
+            ((int)obj.a).IsEqualTo(10);
+            ((int)obj.b).IsEqualTo(20);
+            ((int)obj.c).IsEqualTo(5);
+            ((int)obj.d).IsEqualTo(10);
+            ((int)obj.e).IsEqualTo(5);
+            ((int)obj.f).IsEqualTo(10);
+        }
+
         class Person
         {
             public int PersonId { get; set; }