[英]asp.net core Enum Nullable object must have a value
我有以下enum
:
public enum EventType
{
LoginSuccessfully = 1,
LoginFailure = 2,
UserCreated = 3,
UnableToCreateUser = 4,
PasswordReseted = 5,
UnableToResetPassword = 6,
UserDeleted = 7,
UnableToDeleteUser = 8
}
我有這種方法:
public IActionResult GetFilteredLogs([FromBody] SearchFilterContract contract)
{
//filter logs from database
}
這是從我的方法中作為parameter
接收的contract
:
public class SearchFilterContract
{
public EventType? EventTypes { get; set; }
public string Username { get; set; }
public DateTime? fromDate { get; set; }
public DateTime? toDate { get; set; }
public int pageSize { get; set; }
public int pageNumber {get; set;}
}
如果contract
中的所有值均為Null
,則從數據庫中獲取所有值。
在我的方法上,我比較合同的變量
public SearchStatementSource(int? EventId,string username,DateTime? fromDate,DateTime? toDate,int pageSize, int PageNumber)
{
StringBuilder sb = new StringBuilder();
sb.AppendLine("SELECT * FROM [dbo].[eventslog] ");
if(username != null)
{
sb.AppendLine("WHERE Username = @Username ");
}
else
{
sb.AppendLine("WHERE Username IS NOT NULL ");
}
if(fromDate.HasValue)
{
sb.AppendLine("AND CreatedTime >= @fromDate ");
}
if(toDate.HasValue)
{
sb.AppendLine("AND CreatedTime <= @toDate ");
}
if(EventId.HasValue)
{
sb.AppendLine("AND EventId = @EventId ");
}
sb.AppendLine("AND Id >=" + startingIndex);
sb.AppendLine("AND Id <=" + finalIndex);
_command = sb.ToString();
Parameters.Add(new SqlParameter("@null","null"));
AddNullable("@Username", username);
AddNullable("@EventId", EventId);
AddNullable("@fromDate", fromDate);
AddNullable("@toDate",toDate);
詮釋? EventId是從枚舉接收到的數字
這是我的控制器方法:
[HttpPost]
[Route("[action]")]
[AllowAnonymous]
public IActionResult GetFilteredLogs([FromBody] SearchFilterContract contract)
{
try
{
List<EventsLog> eventsLog = _logsBl.SearchLogs(contract.EventTypes,contract.Username,contract.fromDate,contract.toDate,contract.pageNumber,contract.pageSize);
return Ok(eventsLog);
}
catch(Exception ex)
{
return BadRequest(ex);
}
}
這是我的DataRepository方法
public List<EventsLog> SearchLogs(EventType? EventId, string username, DateTime? fromDate, DateTime? toDate,int pageSize, int pageNumber)
{
List<EventsLog> logs = new List<EventsLog>();
DataTable dt = Select(new SearchStatementSource((int)EventId,username,fromDate,toDate,pageSize,pageNumber));
foreach(DataRow dr in dt.Rows)
{
logs.Add(Map(dr));
}
return logs;
}
當它調用Repository方法SearchStatementSource
方法時,拋出該異常
我的問題是,當我將EventTypes
為Null時,它將返回以下錯誤:
“空對象必須具有值”
有想法該怎么解決這個嗎?
您將必須檢查使用EventTypes.Value
所有位置。
那是因為您正在訪問一個空對象的Value
屬性。
您首先像這樣檢查它:
if(obj.EventTypes.HasValue)
//Do your logic
或者,如果您使用的是C#6,則可以使用它
obj.EventTypes ?? DefaultValue
更新:
您的問題在這里:
DataTable dt = Select(new SearchStatementSource((int)EventId, username, [...]
當EventId
可以為null時,您將其轉換為int
將其更改為(int?)EventId
DataTable dt = Select(new SearchStatementSource((int?)EventId, username, [...]
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