MVC 控制器：在保存之前使用 LINQ 检查表中是否存在重复值？

Question

我的Manufacturers 实体有以下Create() - POST 控制器：

// POST: INV_Manufacturers/Create
// To protect from overposting attacks, please enable the specific properties you want to bind to, for 
// more details see http://go.microsoft.com/fwlink/?LinkId=317598.
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Create([Bind(Include = "Id,manufacturer_description,created_date,created_by,modified_date,modified_by")] INV_Manufacturers iNV_Manufacturers)
{

    iNV_Manufacturers.created_date = DateTime.Now;
    iNV_Manufacturers.created_by = System.Environment.UserName;

    if (ModelState.IsValid == false && iNV_Manufacturers.Id == 0)
    {
        ModelState.Clear();
    }

    if (ModelState.IsValid)
    {
        db.INV_Manufacturers.Add(iNV_Manufacturers);
        await db.SaveChangesAsync();
        return RedirectToAction("Index");
    }

    return View(iNV_Manufacturers);
}

Model 是这样定义的：

public class INV_Manufacturers
{
    public int Id { get; set; }

    [Required(ErrorMessage = "Please enter a Manufacturer.")]
    public string manufacturer_description { get; set; }

    [Required]
    [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
    public DateTime created_date { get; set; }

    [Required]
    public string created_by { get; set; }

    [DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")]
    public DateTime? modified_date { get; set; }

    public string modified_by { get; set; }
}

在我的控制器中使用LINQ 的语法是什么，我可以在其中搜索INV_Manufacturers 表并检查表中是否已经存在具有相同description 的Manufacturer保存在我的Create() 方法中？

伪码：

if (manufacturer.description == ANY.manufacturer.description in Table)
{
    alert("This value already exists in table!");
} else {
    Save(new manufacturer);
}

Answer 1

当然，只需使用.Any()。它将根据是否找到实体返回一个布尔值。在第一次找到它时，它将停止枚举，因此如果它存在，它将快速爆发。如果它不存在，它将检查整个表，并返回 false（这就是 Add 在 !.Any() 中的原因）

if(!db.INV_Manufacturers.Any(m => m.manufacturer_description == iNV_Manufacturers.manufacturer_description))
{
    db.INV_Manufacturers.Add(iNV_Manufacturers);
}
else
{
    //logic for when that description exists
    //for example, to add to ModelState
    ModelState.AddModelError("manufacturer_description","Description Exists");
}