分離物體或使用“AsNoTracking”加載的物體不支持延遲加載

我使用物體框架作為 SQL Server 的 ORM。

這是我的 POST API 中的代碼：

var group = await _context.Groups.FindAsync(id);
            
foreach (CalendarRuleGroup calendarRuleGroup in group.CalendarRuleGroups)
{
    CalendarRule calendarRule = _context.CalendarRules
        .Where(cr => cr.CalendarRuleGroupId == calendarRuleGroup.Id)
        .First();
    
    CalendarRule calendarRuleTemp = (CalendarRule)calendarRule.Clone();
    _context.CalendarRules.Add(calendarRuleTemp);
}

await _context.SaveChangesAsync();

這是 Clone() 函式：

public object Clone()
{
    CalendarRule clonedRule = (CalendarRule)MemberwiseClone();
    clonedRule.Calendar = null;
    clonedRule.CalendarId = default;
    clonedRule.CalendarRuleGroup = null;
    clonedRule.CalendarRuleGroupId = default;
    clonedRule.CalendarContexts = null;
    clonedRule.Id = default;
    List<CalendarRuleCondition> conditions = new List<CalendarRuleCondition>();
    
    foreach (CalendarRuleCondition condition in clonedRule.CalendarRuleConditions)
    {
        conditions.Add((CalendarRuleCondition)condition.Clone());
    }
    
    clonedRule.CalendarRuleConditions = conditions;
    return clonedRule;
}

這是 CalendarRule 的模型：

public class CalendarRule: ICloneable
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime StartingFrom { get; set; }
    public DateTime? Until { get; set; }
    public int? Count { get; set; }
    public double Duration { get; set; }
    public Frequency Frequency { get; set; }
    public int Interval { get; set; }
    public int Priority { get; set; }
    public bool IsWorking { get; set; }
    public int Efficiency { get; set; }
    public int Cost { get; set; }
    public bool AllowedSetup { get; set; }
    public int Color { get; set; }
    public string Description { get; set; }
    public bool? IsActive { get; set; }
    public int CalendarId { get; set; }
    public int? CalendarRuleGroupId { get; set; }
    public virtual Calendar Calendar { get; set; }
    public virtual CalendarRuleGroup CalendarRuleGroup { get; set; }
    public virtual ICollection<CalendarContext> CalendarContexts { get; set; }
    public virtual ICollection<CalendarRuleCondition> CalendarRuleConditions { get; set; }
}

這是foreach中的“clonedRule.CalendarRuleConditions”執行時出現的錯誤：

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HMG79T5K5ECK", Request id "0HMG79T5K5ECK:00000002": An unhandled exception was thrown by the application.
      System.InvalidOperationException: An error was generated for warning 'Microsoft.EntityFrameworkCore.Infrastructure.DetachedLazyLoadingWarning': An attempt was made to lazy-load navigation 'CalendarRuleConditions' on a detached entity of type 'CalendarRuleProxy'. Lazy-loading is not supported for detached entities or entities that are loaded with 'AsNoTracking'. This exception can be suppressed or logged by passing event ID 'CoreEventId.DetachedLazyLoadingWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.

看起來好像“CalendarRule.CalendarRuleConditions”中包含的資料尚未加載。我不使用“AsNoTracking”，并且在我發布的 API 代碼之前沒有對 SaveChangesAsync() 的任何呼叫。我該如何解決這個問題？

uj5u.com熱心網友回復：

這里的代碼沒有任何意義：

foreach (CalendarRuleCondition condition in clonedRule.CalendarRuleConditions)
{
    conditions.Add((CalendarRuleCondition)condition.Clone());
}

clonedRule.CalendarRuleConditions = conditions;

如果您從要克隆的物體實體中呼叫此 Clone() 方法，則應為：

foreach (CalendarRuleCondition condition in CalendarRuleConditions)
{
    conditions.Add((CalendarRuleCondition)condition.Clone());
}

clonedRule.CalendarRuleConditions = conditions;

我們在這個物件的延遲加載的 CalendarRuleConditions 中遍歷每個條件來為克隆構建一個克隆串列。即使這樣，也最好預先加載 CalendarRuleConditions 并且只依賴延遲加載作為后備。

uj5u.com熱心網友回復：

這個問題與其他問題類似。

我認為問題出在，您應該使用(ef) 或(efcore) intead(CalendarRule)MemberwiseClone()創建物體。CreateCreateProxynew

標籤：C＃ 实体框架 asp.net 核心 延迟加载

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