使用.NET Core检查数据库中unique的给定值的最佳方法

Question

我有以下控制器的操作：

public async Task<IActionResult> Create([FromForm]LanguageViewModel viewModel)
{
if (!ModelState.IsValid)
{
return View(viewModel);
}
var newLanguage = new Language()
{
Sort = viewModel.Sort,
LangCode = viewModel.Code,
LangName = viewModel.Name
};
await _languageRepository.SaveAsync(newLanguage);
return RedirectToAction("Index");
}

以及以下viewModel:

public class LanguageViewModel
{
public int Sort { get; set; }
[Required(ErrorMessage = "Language code is required")]
public string Code { get; set; }
[Required(ErrorMessage = "Language name is required")]
public string Name { get; set; }
}

注意，LanguageViewModel不是我的域(实体框架(对象。对于我数据库中的地图，我有另一个：

public class Language
{
public int LanguageId { get; set; }
public int Sort { get; set; }
public string LangName { get; set; }
public string LangCode { get; set; }
}

因此，我正在使用ASP.NET MVC Core 3.1，我需要检查具有给定代码的Language是否已经存在。如果它存在，我想展示关于它的验证错误。你可以说我可以像这样解决它：

public async Task<IActionResult> Create([FromForm] LanguageViewModel viewModel)
{
if (!ModelState.IsValid)
{
return View(viewModel);
}
var lang = await _languageRepository.All.FirstOrDefaultAsync(x =>
x.LangCode.ToUpper() == viewModel.Code.ToUpper());
if (lang != null)
{
ModelState.TryAddModelError("Code", $"The language with code {viewModel.Code} already exists");
}
if (!ModelState.IsValid)
{
return View(viewModel);
}
var newLanguage = new Language()
{
Sort = viewModel.Sort,
LangCode = viewModel.Code,
LangName = viewModel.Name
};
await _languageRepository.SaveAsync(newLanguage);
return RedirectToAction("Index");
}

好的。它是有效的。但它很丑陋：(也许有更好的解决方案？

Answer 1

也许这是一个更干净的解决方案。

if (_languageRepository.Any(o => o.LangCode.Equals(txnId, StringComparison.InvariantCultureIgnoreCase))) 
{
ModelState.TryAddModelError("Code", $"The language with code {viewModel.Code} already exists");
}

Answer 2

最好在EF Core 5:之后尝试一下

https://learn.microsoft.com/en-us/ef/core/modeling/indexes?tabs=data-注释

[Index(nameof(Url), IsUnique = true)]
public class Blog
{
public int BlogId { get; set; }
public string Url { get; set; }
}