[英]How to delete records from database correctly
當我試圖從 wep api 中的數據庫中刪除記錄時,發生錯誤“System.InvalidOperationException:已經有一個打開的 DataReader 與此連接關聯,必須先關閉”。 方法體:
[HttpDelete]
[Route("/DeleteUrls")]
public async Task<IActionResult> DeleteUrls(string userName)
{
var user = _dataContext.Users.FirstOrDefault(x => x.UserName == userName);
if (user==null)
{
return BadRequest("No user with such Username");
}
switch (user.IsAdmin)
{
case true:
var longUrls2Remove = _dataContext.Urls.AsQueryable();
foreach (var item in longUrls2Remove)
{
var shortUrl2Remove = _dataContext.ShortedUrls.FirstOrDefault(x => x.Url == item);
_dataContext.ShortedUrls.Remove(shortUrl2Remove);
_dataContext.Urls.Remove(item);
}
await _dataContext.SaveChangesAsync();
return Ok();
case false:
var longUrlsToRemove = _dataContext.Urls.Where(x => x.UserCreatedBy == user);
foreach (var item in longUrlsToRemove)
{
var shortUrlToRemove = _dataContext.ShortedUrls.FirstOrDefault(x => x.Url == item);
_dataContext.ShortedUrls.Remove(shortUrlToRemove);
_dataContext.Urls.Remove(item);
await _dataContext.SaveChangesAsync();
return Ok();
}
return BadRequest();
}
}
如果用戶是管理員,邏輯是刪除所有記錄,如果不是,則只刪除他自己的記錄。 數據庫結構:
public class User
{
public int Id { get; set; }
public string UserName { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public bool IsAdmin { get; set; }
public List<Url> Urls { get; set; }
}
public class Url
{
public int Id { get; set; }
public string OriginalUrl { get; set; }
public DateTime CreatedAt { get; set; }
public int UserId { get; set; }
public User UserCreatedBy { get; set; }
public ShortUrl ShortUrl { get; set; }
}
public class ShortUrl
{
public int Id { get; set; }
public string ShortedUrl { get; set; }
public int UrlId { get; set; }
public Url Url { get; set; }
}
顯然問題出在另一個開放連接上,但我不知道如何正確實現此方法。
原因:您正在同時執行兩個或多個查詢。
解決方案:在查詢后添加ToList()
。
var longUrlsToRemove = _dataContext.Urls.Where(x => x.UserCreatedBy == user).ToList()
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