linq - 最有效的 Entity Framework 代码第一种扁平化/投影父实体与特定子实体的方法

Question

我有一个父实体 Widget拥有核心成员和多个WidgetTranslation具有语言翻译成员的 child ，即 Description提供英语、法语、德语等文本。

例如

public class Widget
{
  public int Id { get; set; }
  public string Code { get; set; }
  public virtual ICollection<WidgetTranslation> WidgetTranslations { get; set; }
}

public class WidgetTranslation
{
  public int WidgetId { get; set; } 
  public virtual Widget Widget { get; set; }

  public int LanguageId { get; set; }
  public virtual Language Language { get; set; }

  public string Name { get; set; }
  public string Description { get; set; }
  public string Summary { get; set; }
} 

查询小部件集合的最有效方法是什么，为给定的 LanguageId 展平& 投影到 TranslatedWidget DTO

public class TranslatedWidget
{
  public int Id { get; set; }
  public string Code { get; set; }
  public int LanguageId { get; set; }
  public virtual Language Language { get; set; }
  public string Name { get; set; }
  public string Description { get; set; }
  public string Summary { get; set; }
} 

给定 languageId我已经开始了

DbSet.Select(w => new TranslatedWidget
  {
    Id = w.Id,
    Code = w.Code,
    LanguageId = w.LanguageId,
    Name = w.WidgetTranslations.First(wt=>wt.LanguageId == languageId).Name,
    Description = w.WidgetTranslations.First(wt=>wt.LanguageId == languageId).Description,
    Summary = w.WidgetTranslations.First(wt=>wt.LanguageId == languageId).Summary
  });

但我觉得这是低效的，并且不会扩展到 WidgetTranslation 上的更多属性。 .

谢谢

Answer 1

使用 SelectMany 通过单个连接展平结构:

var widgetQuery = from w in dbSet.Widgets
                  from wt in w.WidgetTranslations
                  where wt.Language == languageId
                  select new TranslatedWidget
                  {
                     Id = w.Id,
                     Code = w.Code,
                     LanguageId = w.LanguageId,
                     Name = wt.Name,
                     Description = wt.Description,
                     Summary = wt.Summary
                  });

我在这里假设您对于给定语言的每个小部件只有一个翻译。