API Rest only returns the last value

Question

I am using ASP.Net to create a REST API

I’m trying to create a method that returns a list of groups structured this way:

{
  "IdGroup": "1",
  "NameGroup": "Group1",
  "Installations": [
    {
      "IdInstallation": "1",
      "NameInstallation": "Installation 1"
    },
    {
      "IdInstallation": "2",
      "NameInstallation": "Installation 2"
    },
    {
      "IdInstallation": "3",
      "NameInstallation": "Installation 3"
    },
    {
      "IdInstallation": "4",
      "NameInstallation": "Installation 4"
    }
  ]
}

But my method is only returning the last installation of the group (installation 4, in this case).

My method:

[HttpPost]
[Route ("groups")]
public HttpResponseMessage GetGroups() 
{
    try
    {
        List<Groups> listGroups = new List<Groups>();

        using (SqlConnection connection = new SqlConnection(this.connectionString))
        {
            connection.Open();

            using (SqlCommand command = new SqlCommand())
            {
                command.Connection = connection;
                command.CommandText = "select Groups.IdGroup, Groups.NameGroup, AttributeCloned.IdInstallation, AttributeCloned.NameInstallation " +
                                      "from Groups " +
                                      "join AttributeCloned " +
                                      "on Groups.IdGroup = AttributeCloned.IdGroup "+
                                      "where Groups.IdGroup = 1 "+
                                      "order by IdInstallation asc";

                SqlDataReader reader = command.ExecuteReader();

                Groups group = new Groups();
                Installations inst = new Installations();
                while (reader.Read())
                {
                    group.IdGroup = reader["IdGroup"] == DBNull.Value ? 0 : Convert.ToInt32(reader["IdGroup"]);
                    group.NameGroup = reader["NameGroup"] == DBNull.Value ? string.Empty : reader["NameGroup"].ToString();
                    inst.IdInstallation = reader["IdInstallation"] == DBNull.Value ? 0 : Convert.ToInt32(reader["IdInstallation"]);
                    inst.NameInstallation = reader["NameInstallation"] == DBNull.Value ? string.Empty : reader["NameInstallation"].ToString();
                }

                group.installations.Add(inst);
                listGroups.Add(group);
            }
        }
        return Request.CreateResponse(HttpStatusCode.OK, listGroups.ToArray());
    }
    catch(Exception ex)
    {
        return Request.CreateResponse(HttpStatusCode.BadRequest, ex.Message);
    }
}

What I am missing so that not be returned all the facilities of the respective group?

Answer 1

There’s only one object inst in your code and every iteration it is updated. Place the lines Installations inst = new Installations(); and group.installations.Add(inst); while and the problem should be solved.

However, there is still another problem, this code is only prepared to return a list of groups with only one entry (in this case it is id =1). The problem is both in the query and in the Binding for your model.