在asp.net Web API

Question

我试图在Web api响应中设置Expires标头值，但是即使将其设置为7天后失效，它也无法正常工作。

respMsg.Content.Headers.Expires = DateTimeOffset.Now.AddDays(7);

我将那行代码添加到了HttpResponseMessage中，最后将其返回。在响应标头中，我的Expires字段仍为-1。

下面是我的GET方法代码：

public HttpResponseMessage Get()
{
    List<string> vals = new List<string>();
    using (SqlConnection conn = new SqlConnection(WebConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString))
    {
        using (SqlDataAdapter sda = new SqlDataAdapter())
        {
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = @"                                       
                                    SELECT [ID]
                                    ,[Name]
                                    ,[Age]
                                    FROM [Customers]
                                    ";
                cmd.Connection = conn;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    foreach(DataRow dr in dt.Rows)
                    {
                        vals.Add(dr["Name"].ToString());
                    }
                }
            }
        }
    }
    var respMsg = Request.CreateResponse(HttpStatusCode.OK, vals);
    respMsg.Content.Headers.Expires = DateTimeOffset.Now.AddDays(7);
    return respMsg;
}