(courtesy @mrange) fix dictionary semantics of DapperRow

Dapper NET40/SqlMapper.cs

@@ -1327,7 +1327,7 @@ internal bool FieldExists(string key)
         sealed partial class DapperRowMetaObject : System.Dynamic.DynamicMetaObject
         {
             static readonly MethodInfo getValueMethod = typeof(IDictionary<string, object>).GetProperty("Item").GetGetMethod();
-            static readonly MethodInfo setValueMethod = typeof(DapperRow).GetMethod("SetValue");
+            static readonly MethodInfo setValueMethod = typeof(DapperRow).GetMethod("SetValue", new Type[] { typeof(string), typeof(object) });
 
             public DapperRowMetaObject(
                 System.Linq.Expressions.Expression expression,
@@ -1546,8 +1546,7 @@ IEnumerator IEnumerable.GetEnumerator()
 
             void IDictionary<string, object>.Add(string key, object value)
             {
-                IDictionary<string, object> dic = this;
-                dic[key] = value;
+                SetValue(key, value, true);
             }
 
             bool IDictionary<string, object>.Remove(string key)
@@ -1561,9 +1560,14 @@ IEnumerator IEnumerable.GetEnumerator()
             object IDictionary<string, object>.this[string key]
             {
                 get { object val; TryGetValue(key, out val); return val; }
-                set { SetValue(key, value); }
+                set { SetValue(key, value, false); }
             }
+
             public object SetValue(string key, object value)
+            {
+                return SetValue(key, value, false);
+            }
+            private object SetValue(string key, object value, bool isAdd)
             {
                 if (key == null) throw new ArgumentNullException("key");
                 int index = table.IndexOfName(key);
@@ -1571,10 +1575,21 @@ public object SetValue(string key, object value)
                 {
                     index = table.AddField(key);
                 }
-                if (values.Length <= index)
-                {   // we'll assume they're doing lots of things, and
+                else if (isAdd && index < values.Length && !(values[index] is DeadValue))
+                {
+                    // then semantically, this value already exists
+                    throw new ArgumentException("An item with the same key has already been added", "key");
+                }
+                int oldLength = values.Length;
+                if (oldLength <= index)
+                {
+                    // we'll assume they're doing lots of things, and
                     // grow it to the full width of the table
                     Array.Resize(ref values, table.FieldCount);
+                    for (int i = oldLength; i < values.Length; i++)
+                    {
+                        values[i] = DeadValue.Default;
+                    }
                 }
                 return values[index] = value;
             }

Tests/Tests.cs

@@ -378,6 +378,40 @@ public void TestStrings()
                 .IsSequenceEqualTo(new[] { "a", "b" });
         }
 
+        // see http://stackoverflow.com/questions/16726709/string-format-with-sql-wildcard-causing-dapper-query-to-break
+        public void CheckComplexConcat()
+        {
+            string end_wildcard = @"
+SELECT * FROM #users16726709
+WHERE (first_name LIKE CONCAT(@search_term, '%') OR last_name LIKE CONCAT(@search_term, '%'));";
+
+            string both_wildcards = @"
+SELECT * FROM #users16726709
+WHERE (first_name LIKE CONCAT('%', @search_term, '%') OR last_name LIKE CONCAT('%', @search_term, '%'));";
+
+            string formatted = @"
+SELECT * FROM #users16726709
+WHERE (first_name LIKE {0} OR last_name LIKE {0});";
+
+            string use_end_only = @"CONCAT(@search_term, '%')";
+            string use_both = @"CONCAT('%', @search_term, '%')";
+
+            // if true, slower query due to not being able to use indices, but will allow searching inside strings 
+            bool allow_start_wildcards = false;
+
+            string query = String.Format(formatted, allow_start_wildcards ? use_both : use_end_only);
+            string term = "F"; // the term the user searched for
+
+            connection.Execute(@"create table #users16726709 (first_name varchar(200), last_name varchar(200))
+insert #users16726709 values ('Fred','Bloggs') insert #users16726709 values ('Tony','Farcus') insert #users16726709 values ('Albert','Tenof')");
+
+            // Using Dapper
+            connection.Query(end_wildcard, new { search_term = term }).Count().IsEqualTo(2);
+            connection.Query(both_wildcards, new { search_term = term }).Count().IsEqualTo(3);
+            connection.Query(query, new { search_term = term }).Count().IsEqualTo(2);
+
+        }
+
         enum EnumParam : short
         {
             None, A, B