Question

I need to check for duplicates before saving to the database in the create and edit methods inside my controller. Then I need to display a duplicate error message instead of a generic error message.

My definition of a duplicate is:
userid + Code1ID + Code2ID + Code3ID + Code4ID.

Question:
How to check for a duplicate when the combination of the values above already exists?

Table Name

 Character:
CharacterID int 
UserID int
Code1ID int
Code2ID int
Code3ID int
Code4ID int
Name Varchar(40)

My primary key is composed of UserID + Code1ID + Code2ID + Code3ID + Code4ID.
This guarantees that no duplicates are entered into the database. But the error message I am returning is a general error message.

I need to check for duplicates first and then return a warning message or error message based on the duplication alone.

Here is the edit methods inside the controller

  //
        // GET: /Character/Edit/5

        public ActionResult Edit(int id)
        {
            Character character = db.Characters.Find(id);
        PopulateUserIDDropDownList(character.UserID);
            PopulateCode1IDDropDownList(character.Code1ID);
            PopulateCode2IDDropDownList(character.Code2ID);
            PopulateCode3IDDropDownList(character.Code3ID);
            PopulateCode4IDDropDownList(character.Code4ID);
            return View(character);
        }

        //
        // POST: /Character/Edit/5

        [HttpPost]
        public ActionResult Edit(Character character)
        {
            try
            {
                if (ModelState.IsValid)
                {
                    db.Entry(character).State = EntityState.Modified;
                    db.SaveChanges();
                    return RedirectToAction("Index");
                }
            }
            catch
            {
                ModelState.AddModelError("", "Generic Error. Unable to save changes. Try again, and if the problem persists, see your system administrator.");
            }
        PopulateUserIDDropDownList(character.UserID);
            PopulateCode1IDDropDownList(character.Code1ID);
            PopulateCode2IDDropDownList(character.Code2ID);
            PopulateCode3IDDropDownList(character.Code3ID);
            PopulateCode4IDDropDownList(character.Code4ID);
            return View(character);
        }

Here is the create methods inside the controller

    //
    // GET: /Character/Create

    public ActionResult Create()
    {
    PopulateUserIDDropDownList();
        PopulateCode1IDDropDownList();
        PopulateCode2IDDropDownList();
        PopulateCode3IDDropDownList();
        PopulateCode4IDDropDownList();
        return View();
    } 

    //
    // POST: /Character/Create

    [HttpPost]
    public ActionResult Create(Character character)
    {
        try
        {
            if (ModelState.IsValid)
            {
                db.Characters.Add(character);
                db.SaveChanges();
                return RedirectToAction("Index");
            }
        }
        catch
        {
            ModelState.AddModelError("", "Generic Error.Unable to save changes. Try again, and if the problem persists, see your system administrator.");
        }
    PopulateUserIDDropDownList(character.UserID);
        PopulateCode1IDDropDownList(character.Code1ID);
        PopulateCode2IDDropDownList(character.Code2ID);
        PopulateCode3IDDropDownList(character.Code3ID);
        PopulateCode4IDDropDownList(character.Code4ID);
        return View(character);
    }

Model

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;


namespace myproject.Models
{
    public class Character
    {
        [Key]
        public int CharacterID { get; set; }

        [Required(ErrorMessage = "User is required.")]
        [Display(Name = "User")]
        public Guid UserId { get; set; }

        [Required(ErrorMessage = "Code1 is required.")]
        [Display(Name = "Code1")]
        public int Code1ID { get; set; }


        [Required(ErrorMessage = "Code2 is required.")]
        [Display(Name = "Code2")]
        public int Code2ID { get; set; }

        [Required(ErrorMessage = "Code3 is required.")]
        [Display(Name = "Code3")]
        public int Code3ID { get; set; }

        [Required(ErrorMessage = "Code4 is required.")]
        [Display(Name = "Code4")]
        public int Code4ID { get; set; }

        [Required(ErrorMessage = "level is required.")]
        [Display(Name = "Level")]
        public int LevelID { get; set; }

        public virtual aspnet_Users Aspnet_User { get; set; }
        public virtual Code1 Code1 { get; set; }
        public virtual Code2 Code2 { get; set; }
        public virtual Code3 Code3 { get; set; }
        public virtual Code4 Code4 { get; set; }

    }
}

Answer 1

Before saving to DB… search the DB with those values… if you find something… you have a duplicate and you can display the correct message.

When you are editing, you need to exclude for the query the current object being edited.

You can do a Count() on your repository with those IDs as the WHERE part… if result is 1 or more… you have duplicates.