我在实体框架中找不到带有lambda表达式的“包含”方法吗？

Question

我正在使用实体框架，但找不到此示例中的include方法：

using(ArticleExtractorEntities db=new ArticleExtractorEntities())  
{
    Preference pref= db.Preferences.Include(  

在这里，我只找到包含参数（字符串路径）的函数，而没有找到其他任何重载，那么如何在lambda表达式中使用Include？

Answer 1

它不在System.Linq中。 加

using System.Data.Entity

Answer 2

更新。 对于那些希望通过.Include（）扩展linq查询的人

不再是：

using System.Data.Entity;

使用netcoreapp1.0，它是：

using Microsoft.EntityFrameworkCore;

Answer 3

您可以实现此博客文章中所示的方法 ：

public static class ObjectQueryExtension
{
    public static ObjectQuery<T> Include<T>(this ObjectQuery<T> mainQuery, Expression<Func<T, object>> subSelector)
    {
        return mainQuery.Include(FuncToString(subSelector.Body));
    }
    private static string FuncToString(Expression selector)
    {
        switch (selector.NodeType)
        {
            case ExpressionType.MemberAccess:
                return ((selector as MemberExpression).Member as Reflection.PropertyInfo).Name;
            case ExpressionType.Call:
                var method = selector as MethodCallExpression;
                return FuncToString(method.Arguments[0]) + "." + FuncToString(method.Arguments[1]);
            case ExpressionType.Quote:
                return FuncToString(((selector as UnaryExpression).Operand as LambdaExpression).Body);
        }
        throw new InvalidOperationException();
    }
    public static K Include<T, K>(this EntityCollection<T> mainQuery, Expression<Func<T, object>> subSelector)
        where T : EntityObject, IEntityWithRelationships
        where K : class
    {
        return null;
    }
    public static K Include<T, K>(this T mainQuery, Expression<Func<T, object>> subSelector)
        where T : EntityObject
        where K : class
    {
        return null;
    }
}

Answer 4

请看以下文章：

http://www.thomaslevesque.com/2010/10/03/entity-framework-using-include-with-lambda-expressions/

http://msmvps.com/blogs/matthieu/archive/2008/06/06/entity-framework-include-with-func-next.aspx