return large string data from wcf service in asp.net

I have written WCF service methods that return large string data as below:

string IEmpService.GetEmployeeInfo()
{
    StringBuilder strData = new StringBuilder();
    //create list of user class  
    List<Users> lstUsers = new List<Users>();
    // populate 10000000 data from DB table at a time
    _ods = populateEmpData();// data store to dataset
    // convert dataset to list
    lstUsers = (from dr in _ods.Tables[0].AsEnumerable()
                   select new Users
                   {
                       UsersID = dr.Field<int>("UsersID"),
                       UserName = dr.Field<string>("UserName"),
                       Password = dr.Field<string>("Password")
                   }).ToList();

    // do Serialize of above list  and store it to a string builder(this create huge amount of string dada)     
    strData.Append(Utility.DeSerilization.comonMapper.SerializeList<List<Users>>(lstUsers));
    return strData.ToString(); 
}

User class:

[Serializable]
[XmlRootAttribute(ElementName = "Users", IsNullable = false)]
public class Users
{
    [XmlElement("UsersID")]
    public int UsersID { get; set; }
    [XmlElement("UserName")]
    public string UserName { get; set; }
    [XmlElement("Password")]
    public string Password { get; set; }
}

When I try to run the service it throws the following exception:

strData.ToString()

'strData开发者_开发技巧.ToString()' threw an exception of type 'System.OutOfMemoryException string {System.OutOfMemoryException}

And when I add service reference and show data to a grid view it also shows error.

What is the right approach to return very big string from WCF service?

---

The main problem with trying to grab so much data at once is the massive overhead of desearializing all that data. I would break up the data into more manageable chunks on the server side, and make repeated requests to the service for the next chunk, until there are no chunks left.

I also don't know why you are doing the serialization yourself. I would simply create a data contract to hold your data, and let WCF handle the serialization / deserializeation automatically :)

EDIT:

 [DataContract]
 public class Users
 {
     [DataMember]
     public int UsersID { get; set; }
     [DataMember]
     public string UserName { get; set; }
     [DataMember]
     public string Password { get; set; }
 }

 public List<Users> IEmpService.GetEmployeeInfo()
 {
     //create list of user class  
     List<Users> lstUsers = new List<Users>();
     // populate 10000000 data from DB table at a time
     _ods = populateEmpData();// data store to dataset
     // convert dataset to list
     lstUsers = (from dr in _ods.Tables[0].AsEnumerable()
               select new Users
               {
                   UsersID = dr.Field<int>("UsersID"),
                   UserName = dr.Field<string>("UserName"),
                   Password = dr.Field<string>("Password")
               }).ToList();

     return lstUsers;
 }