Add support of nullable types for DataReaderResult.Single<T>() #47

nreco · May 23, 2018 · f1d7899 · f1d7899
1 parent fd37c03
commit f1d7899
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Showing 2 changed files with 9 additions and 1 deletion.
diff --git a/src/NReco.Data.Tests/DbDataAdapterTests.cs b/src/NReco.Data.Tests/DbDataAdapterTests.cs
@@ -42,6 +42,10 @@ public void Select() {
 			// count for schema-qualified query
 			Assert.Equal(5, DbAdapter.Select( new Query( new QTable( "main.contacts",null) ).Select(QField.Count) ).Single<int>() );
 
+			// select single that is null
+			Assert.False( DbAdapter.Select( new Query("companies", (QField)"id">(QConst)1000).Select(new QField("sum", "sum(size)")) ).Single<int?>().HasValue );
+			Assert.Equal(0, DbAdapter.Select(new Query("companies", (QField)"id" > (QConst)1000).Select(new QField("sum", "sum(size)"))).Single<int>() );
+
 			// count: data view
 			Assert.Equal(5, DbAdapter.Select(new Query("contacts_view").Select(QField.Count) ).Single<int>() );
 

diff --git a/src/NReco.Data/Result/DataReaderResult.cs b/src/NReco.Data/Result/DataReaderResult.cs
@@ -237,6 +237,9 @@ public DataTable ToDataTable(DataTable tbl) {
 #endif
 
 		private T ChangeType<T>(object o, TypeCode typeCode) {
+			if (DataHelper.IsNullOrDBNull(o)) {
+				return default(T);
+			}
 			return (T)Convert.ChangeType(o, typeCode, System.Globalization.CultureInfo.InvariantCulture);
 		}
 
@@ -248,7 +251,8 @@ private Dictionary<string, object> ReadDictionary(IDataReader rdr) {
 		}
 
 		private T Read<T>(IDataReader rdr) {
-			var typeCode = Type.GetTypeCode(typeof(T));
+			var undelyingType = Nullable.GetUnderlyingType(typeof(T));
+			var typeCode = Type.GetTypeCode(undelyingType ?? typeof(T));
 			// handle primitive single-value result
 			if (typeCode!=TypeCode.Object || typeof(T)==typeof(object)) {
 				if (rdr.FieldCount==1) {