diff --git a/modules/swagger-codegen/src/main/resources/csharp/ApiClient.mustache b/modules/swagger-codegen/src/main/resources/csharp/ApiClient.mustache
index 158d087140b..8c5279b6c35 100644
--- a/modules/swagger-codegen/src/main/resources/csharp/ApiClient.mustache
+++ b/modules/swagger-codegen/src/main/resources/csharp/ApiClient.mustache
@@ -232,7 +232,7 @@ namespace {{packageName}}.Client
         /// <param name="contentType">Content type.</param>
         /// <returns>The Task instance.</returns>
         public async System.Threading.Tasks.Task<Object> CallApiAsync(
-            String path, {{^netStandard}}RestSharp.{{/netStandard}}Method method, Dictionary<String, String> queryParams, Object postBody,
+            String path, {{^netStandard}}RestSharp.{{/netStandard}}Method method, List<KeyValuePair<String, String>> queryParams, Object postBody,
             Dictionary<String, String> headerParams, Dictionary<String, String> formParams,
             Dictionary<String, FileParameter> fileParams, Dictionary<String, String> pathParams,
             String contentType)
diff --git a/modules/swagger-codegen/src/main/resources/csharp/api.mustache b/modules/swagger-codegen/src/main/resources/csharp/api.mustache
index e6b9fa5db75..08f416583df 100644
--- a/modules/swagger-codegen/src/main/resources/csharp/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/csharp/api.mustache
@@ -346,7 +346,7 @@ namespace {{packageName}}.{{apiPackage}}
 
             var localVarPath = "{{#netStandard}}.{{/netStandard}}{{{path}}}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -374,7 +374,7 @@ namespace {{packageName}}.{{apiPackage}}
             if ({{paramName}} != null) localVarPathParams.Add("{{baseName}}", Configuration.ApiClient.ParameterToString({{paramName}})); // path parameter
             {{/pathParams}}
             {{#queryParams}}
-            if ({{paramName}} != null) localVarQueryParams.Add("{{baseName}}", Configuration.ApiClient.ParameterToString({{paramName}})); // query parameter
+            if ({{paramName}} != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("{{#collectionFormat}}{{collectionFormat}}{{/collectionFormat}}", "{{baseName}}", {{paramName}})); // query parameter
             {{/queryParams}}
             {{#headerParams}}
             if ({{paramName}} != null) localVarHeaderParams.Add("{{baseName}}", Configuration.ApiClient.ParameterToString({{paramName}})); // header parameter
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/FakeApi.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/FakeApi.cs
index f135081da1e..6cac9990e18 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/FakeApi.cs
@@ -446,7 +446,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -680,7 +680,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -865,7 +865,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -885,9 +885,9 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (enumQueryStringArray != null) localVarQueryParams.Add("enum_query_string_array", Configuration.ApiClient.ParameterToString(enumQueryStringArray)); // query parameter
-            if (enumQueryString != null) localVarQueryParams.Add("enum_query_string", Configuration.ApiClient.ParameterToString(enumQueryString)); // query parameter
-            if (enumQueryInteger != null) localVarQueryParams.Add("enum_query_integer", Configuration.ApiClient.ParameterToString(enumQueryInteger)); // query parameter
+            if (enumQueryStringArray != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "enum_query_string_array", enumQueryStringArray)); // query parameter
+            if (enumQueryString != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_string", enumQueryString)); // query parameter
+            if (enumQueryInteger != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_integer", enumQueryInteger)); // query parameter
             if (enumHeaderStringArray != null) localVarHeaderParams.Add("enum_header_string_array", Configuration.ApiClient.ParameterToString(enumHeaderStringArray)); // header parameter
             if (enumHeaderString != null) localVarHeaderParams.Add("enum_header_string", Configuration.ApiClient.ParameterToString(enumHeaderString)); // header parameter
             if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", Configuration.ApiClient.ParameterToString(enumFormStringArray)); // form parameter
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/Fake_classname_tags123Api.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
index 675474b592a..d31a2bccc95 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
@@ -282,7 +282,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake_classname_test";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/PetApi.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/PetApi.cs
index 46fa3518bcc..9cca7fc41d0 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/PetApi.cs
@@ -602,7 +602,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -763,7 +763,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -913,7 +913,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/findByStatus";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -933,7 +933,7 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (status != null) localVarQueryParams.Add("status", Configuration.ApiClient.ParameterToString(status)); // query parameter
+            if (status != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "status", status)); // query parameter
 
             // authentication (petstore_auth) required
             // oauth required
@@ -1062,7 +1062,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/findByTags";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1082,7 +1082,7 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (tags != null) localVarQueryParams.Add("tags", Configuration.ApiClient.ParameterToString(tags)); // query parameter
+            if (tags != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "tags", tags)); // query parameter
 
             // authentication (petstore_auth) required
             // oauth required
@@ -1211,7 +1211,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1366,7 +1366,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1533,7 +1533,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1695,7 +1695,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}/uploadImage";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/StoreApi.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/StoreApi.cs
index 46cdae27f1b..f556612e151 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/StoreApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/StoreApi.cs
@@ -395,7 +395,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order/{order_id}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -526,7 +526,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/inventory";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -666,7 +666,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order/{order_id}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -810,7 +810,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/UserApi.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/UserApi.cs
index 05d7e8bdada..23079c0ffce 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Api/UserApi.cs
@@ -578,7 +578,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -727,7 +727,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/createWithArray";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -876,7 +876,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/createWithList";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1018,7 +1018,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1155,7 +1155,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1303,7 +1303,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/login";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1323,8 +1323,8 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (username != null) localVarQueryParams.Add("username", Configuration.ApiClient.ParameterToString(username)); // query parameter
-            if (password != null) localVarQueryParams.Add("password", Configuration.ApiClient.ParameterToString(password)); // query parameter
+            if (username != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "username", username)); // query parameter
+            if (password != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "password", password)); // query parameter
 
 
             // make the HTTP request
@@ -1428,7 +1428,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/logout";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1580,7 +1580,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/ApiClient.cs b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/ApiClient.cs
index 7bed82dbcc3..6531cc1a026 100644
--- a/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp/SwaggerClient/src/IO.Swagger/Client/ApiClient.cs
@@ -198,7 +198,7 @@ namespace IO.Swagger.Client
         /// <param name="contentType">Content type.</param>
         /// <returns>The Task instance.</returns>
         public async System.Threading.Tasks.Task<Object> CallApiAsync(
-            String path, RestSharp.Method method, Dictionary<String, String> queryParams, Object postBody,
+            String path, RestSharp.Method method, List<KeyValuePair<String, String>> queryParams, Object postBody,
             Dictionary<String, String> headerParams, Dictionary<String, String> formParams,
             Dictionary<String, FileParameter> fileParams, Dictionary<String, String> pathParams,
             String contentType)
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/FakeApi.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/FakeApi.cs
index f135081da1e..6cac9990e18 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/FakeApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/FakeApi.cs
@@ -446,7 +446,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -680,7 +680,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -865,7 +865,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -885,9 +885,9 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (enumQueryStringArray != null) localVarQueryParams.Add("enum_query_string_array", Configuration.ApiClient.ParameterToString(enumQueryStringArray)); // query parameter
-            if (enumQueryString != null) localVarQueryParams.Add("enum_query_string", Configuration.ApiClient.ParameterToString(enumQueryString)); // query parameter
-            if (enumQueryInteger != null) localVarQueryParams.Add("enum_query_integer", Configuration.ApiClient.ParameterToString(enumQueryInteger)); // query parameter
+            if (enumQueryStringArray != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "enum_query_string_array", enumQueryStringArray)); // query parameter
+            if (enumQueryString != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_string", enumQueryString)); // query parameter
+            if (enumQueryInteger != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "enum_query_integer", enumQueryInteger)); // query parameter
             if (enumHeaderStringArray != null) localVarHeaderParams.Add("enum_header_string_array", Configuration.ApiClient.ParameterToString(enumHeaderStringArray)); // header parameter
             if (enumHeaderString != null) localVarHeaderParams.Add("enum_header_string", Configuration.ApiClient.ParameterToString(enumHeaderString)); // header parameter
             if (enumFormStringArray != null) localVarFormParams.Add("enum_form_string_array", Configuration.ApiClient.ParameterToString(enumFormStringArray)); // form parameter
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/Fake_classname_tags123Api.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
index 675474b592a..d31a2bccc95 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/Fake_classname_tags123Api.cs
@@ -282,7 +282,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/fake_classname_test";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/PetApi.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/PetApi.cs
index 46fa3518bcc..9cca7fc41d0 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/PetApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/PetApi.cs
@@ -602,7 +602,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -763,7 +763,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -913,7 +913,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/findByStatus";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -933,7 +933,7 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (status != null) localVarQueryParams.Add("status", Configuration.ApiClient.ParameterToString(status)); // query parameter
+            if (status != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "status", status)); // query parameter
 
             // authentication (petstore_auth) required
             // oauth required
@@ -1062,7 +1062,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/findByTags";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1082,7 +1082,7 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (tags != null) localVarQueryParams.Add("tags", Configuration.ApiClient.ParameterToString(tags)); // query parameter
+            if (tags != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("csv", "tags", tags)); // query parameter
 
             // authentication (petstore_auth) required
             // oauth required
@@ -1211,7 +1211,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1366,7 +1366,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1533,7 +1533,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1695,7 +1695,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/pet/{petId}/uploadImage";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/StoreApi.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/StoreApi.cs
index 46cdae27f1b..f556612e151 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/StoreApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/StoreApi.cs
@@ -395,7 +395,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order/{order_id}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -526,7 +526,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/inventory";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -666,7 +666,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order/{order_id}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -810,7 +810,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/store/order";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/UserApi.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/UserApi.cs
index 05d7e8bdada..23079c0ffce 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/UserApi.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Api/UserApi.cs
@@ -578,7 +578,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -727,7 +727,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/createWithArray";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -876,7 +876,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/createWithList";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1018,7 +1018,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1155,7 +1155,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1303,7 +1303,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/login";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1323,8 +1323,8 @@ namespace IO.Swagger.Api
             if (localVarHttpHeaderAccept != null)
                 localVarHeaderParams.Add("Accept", localVarHttpHeaderAccept);
 
-            if (username != null) localVarQueryParams.Add("username", Configuration.ApiClient.ParameterToString(username)); // query parameter
-            if (password != null) localVarQueryParams.Add("password", Configuration.ApiClient.ParameterToString(password)); // query parameter
+            if (username != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "username", username)); // query parameter
+            if (password != null) localVarQueryParams.AddRange(Configuration.ApiClient.ParameterToKeyValuePairs("", "password", password)); // query parameter
 
 
             // make the HTTP request
@@ -1428,7 +1428,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/logout";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
@@ -1580,7 +1580,7 @@ namespace IO.Swagger.Api
 
             var localVarPath = "/user/{username}";
             var localVarPathParams = new Dictionary<String, String>();
-            var localVarQueryParams = new Dictionary<String, String>();
+            var localVarQueryParams = new List<KeyValuePair<String, String>>();
             var localVarHeaderParams = new Dictionary<String, String>(Configuration.DefaultHeader);
             var localVarFormParams = new Dictionary<String, String>();
             var localVarFileParams = new Dictionary<String, FileParameter>();
diff --git a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Client/ApiClient.cs b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Client/ApiClient.cs
index 7bed82dbcc3..6531cc1a026 100644
--- a/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp/SwaggerClientWithPropertyChanged/src/IO.Swagger/Client/ApiClient.cs
@@ -198,7 +198,7 @@ namespace IO.Swagger.Client
         /// <param name="contentType">Content type.</param>
         /// <returns>The Task instance.</returns>
         public async System.Threading.Tasks.Task<Object> CallApiAsync(
-            String path, RestSharp.Method method, Dictionary<String, String> queryParams, Object postBody,
+            String path, RestSharp.Method method, List<KeyValuePair<String, String>> queryParams, Object postBody,
             Dictionary<String, String> headerParams, Dictionary<String, String> formParams,
             Dictionary<String, FileParameter> fileParams, Dictionary<String, String> pathParams,
             String contentType)