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How to update a record in database in Entity Framework?

I'm using c# mvc with EF and i'm building a website. When i'm updating a table with new values it gives the following error.
{"Violation of PRIMARY KEY constraint 'PK_Table_1_1'. Cannot insert duplicate key in object 'dbo.User'. The duplicate key value is (shan#gmail.com).\r\nThe statement has been terminated."}
Here is my design of the table.
Here is my controller file
[HttpPost]
public ActionResult Manage(ManageViewModel manageviewmodel)
{
TheFoodyContext db = new TheFoodyContext();
string UserEmail = Session["UserEmail"].ToString();
User user_to_update = db.Users.Find(UserEmail);
if (ModelState.IsValid)
{
try
{
HttpPostedFileBase photo = Request.Files["photo"];
if (photo != null && photo.ContentLength > 0)
{
var path = "";
var fileName = Path.GetFileName(photo.FileName);
var extension = Path.GetExtension(photo.FileName);
var allowedExtensions = new[] {".Jpg", ".png", ".jpg", "jpeg"};
if (allowedExtensions.Contains(extension))
{
string name = Path.GetFileNameWithoutExtension(fileName);
string myfile = name + "_" + UserEmail + extension;
path= Path.Combine(Server.MapPath("~/Img"), myfile);
photo.SaveAs(path);
user_to_update.photo = myfile;
}
else
{
ViewBag.message = "Please choose only Image file";
}
user_to_update.email = UserEmail;
user_to_update.fname = manageviewmodel.FirstName;
user_to_update.lname = manageviewmodel.LastName;
user_to_update.phone = manageviewmodel.Phone;
user_to_update.address = manageviewmodel.Address;
user_to_update.city = manageviewmodel.City;
user_to_update.postcode = Convert.ToDecimal(manageviewmodel.PostCode);
user_to_update.district = manageviewmodel.District;
user_to_update.user_type = manageviewmodel.UserType;
user_to_update.status = manageviewmodel.Status;
user_to_update.photo = path;
db.Users.Add(user_to_update);
db.SaveChanges();
Session["UserEmail"] = UserEmail;
Session["FirstName"] = manageviewmodel.FirstName;
Session["LastName"] = manageviewmodel.LastName;
Session["Address"] = manageviewmodel.Address;
Session["City"] = manageviewmodel.City;
Session["PostCode"] = manageviewmodel.PostCode;
Session["District"] = manageviewmodel.District;
Session["UserType"] = manageviewmodel.UserType;
Session["Status"] = manageviewmodel.Status;
Session["Phone"] = manageviewmodel.Phone;
return RedirectToAction("Manage");
}
}
catch (Exception ex)
{
return View(ex.Message);
}
return View(manageviewmodel);
}
return View(manageviewmodel);
}
Here is my Model file
public class ManageViewModel
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string Email { get; set; }
public string Phone { get; set; }
public string photo { get; set; }
public string Address { get; set; }
public string City { get; set; }
public int PostCode { get; set; }
public string District { get; set; }
public string UserType { get; set; }
public string Status { get; set; }
}

You don't need to add the user again (it already exists and EF tracks changes), simply call SaveChanges and you are done.
Just remove this line:
db.Users.Add(user_to_update);
and it should work (unless there are more errors).

Cannot initialize type 'PeopleModel' with a collection initializer because it does not implement 'System.Collections.IEnumerable'

I have a method that aims to fill a PersonModel from OleDB;
public IEnumerable<PeopleModel> GetPeopleDetails()
{
var constr = ConfigurationManager.ConnectionStrings["dbfString"].ConnectionString;
using (var dbfCon = new OleDbConnection(constr))
{
dbfCon.Open();
using (var dbfCmd = dbfCon.CreateCommand())
{
dbfCmd.CommandText = "SELECT pp_firstname, pp_surname, pp_title, pp_compnm, pp_hmaddr1, pp_hmaddr2, pp_hmtown, pp_hmcounty, pp_hmpcode, pp_spouse, pp_children FROM people ORDERBY pp_surname";
using (var myReader = dbfCmd.ExecuteReader())
{
var peopleList = new List<PeopleModel>();
while (myReader.Read())
{
var details = new PeopleModel
{
details.Firstname = myReader[0].ToString(),
details.Lastname = myReader[1].ToString(),
details.Title = myReader[2].ToString(),
details.Company = myReader[3].ToString(),
details.Addr1 = myReader[4].ToString(),
details.Addr2 = myReader[5].ToString(),
details.Town = myReader[6].ToString(),
details.County = myReader[7].ToString(),
details.Spouse = myReader[8].ToString(),
details.Children = myReader[9].ToString(),
};
peopleList.Add(details);
}
return peopleList;
}
}
}
}
This code is pretty much identical to the method I am using to fill a companies details, which works no problem. Here is the PeopleModel I am using to build a person.
namespace SdcDatabase.Model
{
public class PeopleModel
{
public string Firstname { get; set; }
public string Lastname { get; set; }
public string Title { get; set; }
public string Company { get; set; }
public string Addr1 { get; set; }
public string Addr2 { get; set; }
public string Town { get; set; }
public string County { get; set; }
public string Spouse { get; set; }
public string Children { get; set; }
}
}
Although the companies method has worked fine previously, I am now getting the following error when I try to build my project after implementing the People code: Cannot initialize type 'PeopleModel' with a collection initializer because it does not implement 'System.Collections.IEnumerable'
I really am at a lost cause with this as it is working in an almost identical method for a Company.

Correct syntax, without details. in the assignments in the initializer:
var details = new PeopleModel
{
Firstname = myReader[0].ToString(),
Lastname = myReader[1].ToString(),
Title = myReader[2].ToString(),
Company = myReader[3].ToString(),
Addr1 = myReader[4].ToString(),
Addr2 = myReader[5].ToString(),
Town = myReader[6].ToString(),
County = myReader[7].ToString(),
Spouse = myReader[8].ToString(),
Children = myReader[9].ToString(),
};

Get PK value by passing in non-PK value using EntityFramework

I'm working on building a Windows Phone 8.1 app that uses a Web API and Entity Framework to connect to a SQL database. With my current setup, I have data objects for my entities in my services project (which contain the PK id property) and models in my phone client project (which don't contain the PK id property in order to enable auto-increment when a new member is created. I'm trying to write a services method that returns the memberID value (PK of Member entity) when the username is passed to it. However, when I do so, I get the following error:
System.InvalidCastException: Unable to cast object of type 'System.Net.Http.StreamContent' to type 'System.IConvertible'.
I'm not sure if I'm trying to do something that doesn't work, or if there's a much easier way to do this, but my code builds successfully. The above error is a run-time error. Here's the code I'm using for my relevant classes:
This is the method that calls my server from my client's backend:
public async void GetMembers(String currUser, String currPass)
{
using (var client = new HttpClient())
{
//MembersListBox.Items.Add("using block entered");
client.BaseAddress = new Uri("http://nflff.azurewebsites.net");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
//MembersListBox.Items.Add("client's defaultrequestheaders done");
//gets all members from table
HttpResponseMessage response = await client.GetAsync("api/Members");
//MembersListBox.Items.Add("after response reached");
if (response.IsSuccessStatusCode)
{
//reads all member objs from table as a json string
string s = await response.Content.ReadAsStringAsync();
//how can we pass the user's login credentials (including ID) to other pages? via HttpClient?
//converts string of members into a list of member objs
var deserializedResponse = JsonConvert.DeserializeObject<List<Members>>(s);
foreach (Members member in deserializedResponse)
{
//if current member matches a member found in list
if(member.compareUserAndPassword(currUser, currPass)) {
MembersListBox.Items.Add(currUser + " and " + currPass + " found.");
MembersListBox.Items.Add(member.userName + " " + member.password);
Members currMember = member; //this works
MembersListBox.Items.Add("Current member: " + currMember.ToString());
//how should memberID be remembered for user?
client.DefaultRequestHeaders.Authorization = CreateBasicHeader(currUser, currPass);
MembersListBox.Items.Add(client.DefaultRequestHeaders.Authorization);
HttpResponseMessage memResponse = await client.GetAsync("api/Members/" + currUser);
if (memResponse.IsSuccessStatusCode)
{
MembersListBox.Items.Add("memResponse successful");
}
//should only go to home page if successful
//int memID = Convert.ToInt32(await client.GetAsync("api/Members?MemberStr=" + currUser));
HttpResponseMessage thisMember = await client.GetAsync("api/Members?MemberStr=" + currUser);
var con = thisMember.Content;
var head = thisMember.Headers;
var rm = thisMember.RequestMessage;
int memID = Convert.ToInt32(thisMember.Content);//THIS IS THE LINE THAT GENERATES THE ERROR
//will need to call server's getidbyname method and pass result instead of currMember.memberID
//this.Frame.Navigate(typeof(HomeHub), currMember.memberID);
this.Frame.Navigate(typeof(HomeHub), memID);
}
}
}
//MembersListBox.Items.Add(Members.MembersList.Count);
foreach (var member in Members.MembersList)
{
// MembersListBox.Items.Add(member.ToString());
}
}
}
Here's my controller from my services project:
public class MembersController : ApiController
{
private GatoradeShowerDB db = new GatoradeShowerDB();
// GET: api/Members
public IQueryable<Member> GetMembers()
{
return db.Members;
}
// GET: api/Members/5
[ResponseType(typeof(Member))]
public async Task<IHttpActionResult> GetMember(int id)
{
Member member = await db.Members.FindAsync(id);
if (member == null)
{
return NotFound();
}
return Ok(member);
}
//GET: api/Members?MemberStr={memberStr}
[ResponseType(typeof(Member))]
public async Task<T> GetMemberIDByName<T>(String MemberStr) where T : struct
{
//var member = JsonConvert.DeserializeObject<Member>(MemberStr);
//Member member = await db.Members.FindAsync(MemberStr);
//var userId = ...;
var member = await db.Members.Where(x => x.UserName == MemberStr).ToListAsync();
if (member == null)
{
return (T)Convert.ChangeType(NotFound(), typeof(T));
}
return (T)Convert.ChangeType(member[0].MemberID, typeof(T));
//return member[0].MemberID; //hopefully gets id of first member in async list and returns it
//return Ok(member);
}
//other methods
}
Also, here's my client-side model:
public class Members
{
//[JsonProperty("MemberID")]
//public int memberID { get; private set; }
[JsonProperty("FirstName")]
private string firstName { get; set; }
[JsonProperty("LastName")]
private string lastName { get; set; } //both names should be optional
[JsonProperty("UserName")]
public string userName { get; private set; } //note: I don't think we should track first and last names
[JsonProperty("Password")]
public string password { get; private set; } //will probably need to implement validation in setter so won't be able to auto-implement
[JsonProperty("Email")]
private string email { get; set; }//same with this. will need validation
[JsonProperty("MemberCity")]
private string memberCity { get; set; }
[JsonProperty("MemberState")]
private string memberState { get; set; }
[JsonProperty("MemberZip")]
private string memberZip { get; set; }
[JsonProperty("MemberPhone")]
private string memberPhone { get; set; }//should also be optional
[JsonProperty("FaveTeamID")]
private int faveTeamID { get; set; }
public static List<Members> MembersList = new List<Members>();
public Members(string first, string last, string user, string pass, string email, string city, string state, string zip, string phone, int team)
{
//memberID = id;
firstName = first;
lastName = last;
userName = user;
password = pass;
this.email = email;
memberCity = city;
memberState = state;
memberZip = zip;
memberPhone = phone;
faveTeamID = team;
}
public override string ToString()
{
return "Member: " + userName + " in " + memberCity;
}
public bool compareUserAndPassword(string currUser, string currPass)
{
if (currUser.Equals(userName) && currPass.Equals(password))
{
return true;
}
else
{
return false;
}
}
}
Finally, here's my server-side data object:
public partial class Member
{
public int MemberID { get; set; }
[Required]
[StringLength(255)]
public string FirstName { get; set; }
[Required]
[StringLength(255)]
public string LastName { get; set; }
[Required]
[StringLength(50)]
public string UserName { get; set; }
[Required]
[StringLength(32)]
public string Password { get; set; }
[Required]
[StringLength(50)]
public string Email { get; set; }
[Required]
[StringLength(50)]
public string City { get; set; }
[Required]
[StringLength(30)]
public string State { get; set; }
[Required]
[StringLength(255)]
public string Zip { get; set; }
[Required]
[StringLength(255)]
public string Phone { get; set; }
public int FavTeamID { get; set; }
}
I know this is a lot of code, but I'd rather post too much than too little. One thought I had was to somehow add the MemberID value to the httpClient object and pass that as a parameter to other pages, but I'm not sure if that's possible either. How can I get the MemberID value for a specific member if that value is only stored in the server-side data object but not in the client-side model? I'm open to different approaches as well if there's an easier way to go about this. Thank you in advance for your help.
UPDATE
My issue seems to be originating from my GetMemberIDByName method in my controller. When I debugged it, I got the following error message:
Cannot call action method 'System.Threading.Tasks.Task`1[T] GetMemberIDByNameT' on controller 'WorkingVersionGetItDone.Controllers.MembersController' because the action method is a generic method.

I'm pretty sure your method should look more like this:
public async Task<IHttpActionResult> GetMemberIDByName(string MemberStr)
{
var member = await db.Members.Where(x => x.UserName == MemberStr).ToListAsync();
if (member == null)
{
return NotFound();
}
return Ok(member[0].MemberID);
}
The caller will then either get a 404 (the NotFound()) or a 200 with a payload of the MemberID and you can process appropriately.
HttpResponseMessage memberResponse = await client.GetAsync("api/Members?MemberStr=" + currUser);
if(memberResponse.StatusCode == HttpStatusCode.OK)
{
// got the memberId...
var memberId = Convert.ToInt32( memberResponse.Content.ReadAsStringAsync().Result);
}
else if(memberResponse.StatusCode == HttpStatusCode.NotFound)
{
// member not found...
}

How do I extend a model class to another model?

I am trying to extend a class to another class that will collect them as a list.
model:
public class Brand
{
public int BrandId { get; set; }
public string Name { get; set; }
public string Guid { get; set; }
public float Rating { get; set; }
public string Industry { get; set; }
public string Address1 { get; set; }
public string Address2 { get; set; }
public string City { get; set; }
public string State { get; set; }
public string Postal { get; set; }
public string CountryCode { get; set; }
public virtual Snapshot Snapshot { get; set; }
}
public class Snapshot
{
public int ID { get; set; }
public string Guid { get; set; }
public int CompanyID { get; set; }
public string CompanyName { get; set; }
public string Email { get; set; }
public DateTime DateTimeSent { get; set; }
public string Subject { get; set; }
public string Html { get; set; }
public string Image { get; set; }
public string Unsubscribe { get; set; }
}
public class BrandSnaphotViewModel
{
public Brand Brand { get; set; }
public List<Snapshot> SnapshotItems { get; set; }
}
controller:
public ActionResult Index(string brandGuid)
{
BrandSnaphotViewModel viewModel = new BrandSnaphotViewModel();
Brand brand = GetBrand(brandGuid);
viewModel.Brand = brand;
List<Snapshot> snapshot = GetBrandSnapshots(brand.BrandId);
viewModel.SnapshotItems = snapshot;
List<BrandSnaphotViewModel> viewModelList = new List<BrandSnaphotViewModel>();
viewModelList.Add(viewModel);
return View(viewModelList.AsEnumerable());
}
private Brand GetBrand(string brandGuid)
{
Brand brand = new Brand();
string dbConnString = WebConfigurationManager.ConnectionStrings["dbConn"].ConnectionString;
MySqlConnection dbConn = new MySqlConnection(dbConnString);
dbConn.Open();
MySqlCommand dbCmd = new MySqlCommand();
dbCmd.CommandText = "SELECT *, industries.name AS industry_name FROM brands LEFT JOIN industries ON brands.industry_id = industries.industry_id WHERE brand_guid = '" + brandGuid.ToString() + "' AND private = 0 LIMIT 1";
dbCmd.Connection = dbConn;
MySqlDataReader dbResult = dbCmd.ExecuteReader();
if (dbResult.Read())
{
brand.Guid = dbResult["brand_guid"].ToString();
brand.BrandId = Convert.ToInt32(dbResult["brand_id"]);
brand.Industry = dbResult["industry_name"].ToString();
}
dbResult.Close();
dbConn.Close();
return brand;
}
private List<Snapshot> GetBrandSnapshots(int brandId)
{
string dbConnString = WebConfigurationManager.ConnectionStrings["dbConn"].ConnectionString;
MySqlConnection dbConn = new MySqlConnection(dbConnString);
dbConn.Open();
MySqlCommand dbCmd = new MySqlCommand();
dbCmd.CommandText = "SELECT * FROM snapshots WHERE brand_id = " + brandId + " AND archive = 0 ORDER BY date_sent DESC";
dbCmd.Connection = dbConn;
MySqlDataReader dbResult = dbCmd.ExecuteReader();
List<Snapshot> snapshots = new List<Snapshot>();
while (dbResult.Read())
{
snapshots.Add(new Snapshot
{
SnapshotId = Convert.ToInt32(dbResult["snapshot_id"]),
Subject = dbResult["subject"].ToString(),
DateTimeSent = Convert.ToDateTime(dbResult["date_sent"]),
Image = dbResult["image"].ToString(),
Email = dbResult["email"].ToString(),
ContentType = dbResult["content_type"].ToString(),
Type = dbResult["type"].ToString()
});
}
dbResult.Close();
dbConn.Close();
return snapshots;
}
edit
FIXED
The issue was the VIEW was not referencing the ViewModel as an IENumerable<>. FACEPALM.
#model IEnumerable<projectvia.ViewModels.BrandSnaphotViewModel>
#{
ViewBag.Title = "Index";
}
#foreach(var item in Model)
{
#item.Brand.Guid;
for(int i = 0; i< #item.SnapshotItems.Count; i++)
{
#item.SnapshotItems[i].Subject<br/>
}
}
That resolved the issue.
Thank you both experts for the insights... i took both advice and came to this solution.

you are doing wrong, it is a list.
you cannot add element this way. Create object and add that object in list by calling Add()
do like this to add items in it:
List<BrandEmailList> brandSnapshotsList = new List<BrandEmailList>();
while (dbResult.Read())
{
BrandEmailList brandSnapshots = new BrandEmailList (); // create an object
brandSnapshots.ID = Convert.ToInt32(dbResult["snapshot_id"]);
brandSnapshots.Guid = dbResult["snapshot_guid"].ToString();
brandSnapshots.DateTimeSent = dbResult["date_sent"];
brandSnapshots.Subject = dbResult["subject"].ToString();
brandSnapshots.Image = dbResult["image"];
brandSnapshotsList.Add(brandSnapshots); // add it in list
}
EDIT:
List is a generic thing, you don't need to create a class for it. you can just instantiate a list and add items in it.
why are you doing like that you can do it this way simply:
List<Snapshot> brandSnapshotsList = new List<Snapshot>();
while (dbResult.Read())
{
Snapshot brandSnapshots = new Snapshot(); // create an object
brandSnapshots.ID = Convert.ToInt32(dbResult["snapshot_id"]);
brandSnapshots.Guid = dbResult["snapshot_guid"].ToString();
brandSnapshots.DateTimeSent = dbResult["date_sent"];
brandSnapshots.Subject = dbResult["subject"].ToString();
brandSnapshots.Image = dbResult["image"];
brandSnapshotsList.Add(brandSnapshots); // add it in list
}

Building on what Ehsan Sajjad did, looking at public IEnumerator<Snapshot> BrandEmails, i believe what you look for looks more like this:
public class Snapshot
{
public int ID { get; set; }
public string Guid { get; set; }
// ...
}
public class BrandEmailList : List<Snapshot>
{
}
You need not even create a new type for your brand email list, you can use List<Snapshot> directly.
public ViewResult Whatever() {
var brand = GetBrand(brandName);
var brandSnapshots = GetBrandSnapshots();
return View(brand, brandSnapshots);
}
private Brand GetBrand(string brandName)
{
try
{
var brand = new Brand();
brand.Name = brandName;
// database stuffs ...
return brand;
}
catch (Exception ex)
{
throw ex;
}
}
private List<Snapshot> GetBrandSnapshots()
{
// ...
// DB stuffs -- that *really* should not be in the controller anyways.
// ...
var snapshots = new List<BrandEmailList>();
while (dbResult.Read())
{
// object initializer syntax
snapshots.Add(new Snapshot {
ID = Convert.ToInt32(dbResult["snapshot_id"]),
Guid = dbResult["snapshot_guid"].ToString(),
DateTimeSent = dbResult["date_sent"],
Subject = dbResult["subject"].ToString(),
Image = dbResult["image"],
});
}
return snapshots
}
As a side note, mixing database access into controller methods can be a bad idea. It does not have to be, but it can be. Generally, fetching data from the database happens at a different "level" than serving a MVC result. MVC controller don't have the "purpose" to talk to a database, that work can/should be delegated to a dedicated type. Compare the single responsibility principle part of the SOLID principles.

Adding a list to a dictionary

In my program I have a list of marks and a dictionary which stores the studentId. I want that the user enters the studentId and according to that id it will point to the list of marks. I think I am implementing it incorrectly. Can someone help me in implementing it. Thanks
public class Student() {
private string name;
private string surname;
private string dob;
private string address;
private int id;
public Student()
{
}
public Student(string year,string name, string surname, string dob, string address)
{
this.name = name;
this.surname = surname;
this.dob = dob;
this.address = address;
this.year = year;
}
public string Name
{
get { return name; }
set { name = value; }
}
public string Surname
{
get { return surname; }
set { surname = value; }
}
public string DOB
{
get { return dob; }
set { dob = value; }
}
public string Addr
{
get { return address; }
set { address = value; }
}
public int Id
{
get { return id; }
set { id = value; }
}
private string year;
public string Year
{
get { return year; }
set { year = value; }
}
public Student(string s)
{
string[] splitted = s.Split(',');
name = splitted[0];
surname = splitted[1];
dob = splitted[2];
address = splitted[3];
// id = splitted[4];
}
public Dictionary<int,List<Marks>> dictionary= new Dictionary<int,List<Marks>>();
public List<Marks> Mathematics = new List<Marks>();
public List<Marks> English = new List<Marks>();
public List<Marks> Maltese = new List<Marks>();
public List<Marks> ReligiousStudies = new List<Marks>();
public List<Marks> SocialStudies = new List<Marks>();
public Dictionary<int, List<Marks>> dictionar = new Dictionary<int, List<Marks>>();
public void AddMarks(int hyexam, int anexam)
{
{
Console.WriteLine("enter id of student to input marks to:");
string id = Console.ReadLine();
if (dictionar.ContainsKey(Id).Equals(id))
{
Mathematics.Add(new Marks(hyexam, anexam));
English.Add(new Marks(hyexam, anexam));
Maltese.Add(new Marks(hyexam, anexam));
ReligiousStudies.Add(new Marks(hyexam, anexam));
SocialStudies.Add(new Marks(hyexam, anexam));
dictionar.Add(id, (Mathematics)); //dont know how to implement it
}
else
{
Console.WriteLine("id not found");
}
}
}
public class Marks
{
private int hyexam;
private int anexam;
private string id;
public int HYEXAM
{
get { return hyexam; }
set { hyexam = value; }
}
public int ANEXAM
{
get { return anexam; }
set { anexam = value; }
}
public string Id
{
get { return id; }
set { id = value; }
}
public Marks(int hyexam, int anexam)
{
this.hyexam = hyexam;
this.anexam = anexam;
}
public Marks(string id)
{
this.id = id;
}
public double OverallExam()
{
return (0.4 * hyexam) + (0.6 * anexam);
}
}
}

I'd say the main problem is your modelling. You've included the Dictionary<int, List<Marks>> as a field within Student. That means that each Student object has a dictionary. That makes no sense - because the key for the dictionary is meant to be the student ID, right?
It probably makes sense for each Student object to the lists of marks as you've currently got (although not as public fields, IMO). Given that information, do you really need a Dictionary going to the marks at all? Wouldn't it be cleaner to have a Dictionary<int, Student> somewhere (not in the Student class - maybe in a School class?) mapping each student ID to a Student, and you can get the marks from the Student?
Think hard about what you're trying to achieve, and where the data really belongs. In my experience, when you've got the data modelling right, the code usually follows in a clean way.
(I'd also question your Marks class, both in terms of name and design. What are those properties meant to represent? Isn't it really a single mark in an exam? Perhaps ExamResult would be clearer? Does it really need to be mutable?)

I'd agree with Jon that this is definitely a modeling issue (based on the OP's other posts). If you're new to object oriented programming, the first thing you need to do is determine what objects you'll need to create to answer the problem.
What is a Student? A student has a name, id, dob, class year, etc. For every attribute a student has, you need to set up a field or property.
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public DateTime DoB { get; set; }
... etc ...
}
What is a Mark? From your descriptions, a Mark has a subject, a mid-exam score, and an annual-exam score.
public class Mark
{
public string Subject { get; set; }
public int MidScore { get; set; }
public int FinalScore { get; set; }
}
What is the relationship between a Student and a Mark? A student has a list of marks associated with them. This is best described with a List<> object.
public class Student() // continued
{
public List<Mark> Marks { get; set; }
}
Once you have the basics set up for your objects, it will be easier to filter out what you DON'T need, and make it much easier to answer your question. :)

My proposal:
Your "Mark" class must have something that identifies the subject (could be an enum called Subject, or an string, or an int with the ID of the subject if you have it stored in database)
Then you could have:
Console.WriteLine("enter id of student to input marks to:");
string id = Console.ReadLine();
var marks = new Dictionary<int, List<Mark>>();
if (UserExists(id))
{
Console.WriteLine("mark for subject1:");
string s1 = Console.ReadLine();
Console.WriteLine("mark for subject2:");
string s2 = Console.ReadLine();
var list = new List<Mark>();
list.Add(new Mark { Subject = SubjectEnum.Subject1, Value = Convert.ToDecimal(s1), });
list.Add(new Mark { Subject = SubjectEnum.Subject2, Value = Convert.ToDecimal(s2), });
marks.Add(Convert.ToInt32(id), list)
}
else
{
Console.WriteLine("id not found");
}
Hope this helps.