entity-framework - IsLoaded用于自跟踪实体

Question

我将自跟踪实体与EF 4.0一起使用，我发现导航对象没有IsLoaded属性，该对象与标准EF对象一样具有多对多关系。因此，如果您要查询Person而不包含地址，那么person.Addresses会出现一个空列表，但是无法判断地址是否已加载或该人没有任何地址。

有没有办法判断导航属性是否已加载到自跟踪实体上？

如果没有，那么有一种方法可以从ObjectContext访问当前的ObjectQuery，这样我就可以查看用户尝试扩展哪些属性并创建自定义IsLoaded属性？

Answer 1

不幸的是，我最初的计划在HandleObjectMaterialized方法（从ObjectMaterialized事件中调用）中填充自跟踪实体上的IsLoaded属性并没有按期望的那样工作，因为许多集合仅在事件之后被填充（请参见this帖子） ）。我想遍历上下文中每个被跟踪实体的关系，测试IsLoaded属性并在我的自跟踪实体上设置相应的IsLoaded属性。

因此，我改为为First（）和ToList（）创建扩展方法，称为FirstWithLoaded（）和ToListWithLoaded（），以便为此使用反射：

public static T FirstOrDefaultWithLoaded<T>(this IQueryable<T> source) where T : new()
        {     
            T result = default(T);
            if (source != null)
            {       
                //Call the base FirstOrDefault
                result = source.FirstOrDefault();

                var querySource = source as ObjectQuery<T>;
                if (querySource != null)
                {
                    PopulateIsLoaded(result, querySource.Context);
                }
            }
            return result;
        }

        private static void PopulateIsLoaded(object inputEntity, ObjectContext dataContext)
        {
            var entry = dataContext.ObjectStateManager.GetObjectStateEntry(inputEntity);

            //var relationShipManagerProperty = entryType.GetProperty("RelationshipManager");//.GetValue(entityType, null);
            var relationShipManager = GetPropertyValue(entry, "RelationshipManager");// relationShipManagerProperty.GetValue(entry, null);

            if (relationShipManager != null)
            {
                //get the relationships (this is a sealed property)
                var relationships = GetPropertyValue(relationShipManager, "Relationships") as IEnumerable<RelatedEnd>;

                if (relationships != null)
                {
                    foreach (RelatedEnd relationship in relationships)
                    {
                        //check to see whether the relationship is loaded
                        var isLoaded = GetRelatedEndPropertyValue(relationship, "IsLoaded");

                        if (isLoaded != null && (bool)isLoaded)
                        {
                            //if the relationship is loaded then set the
                            //<NavigationPropertyName>IsLoaded on entry to true
                            var navigationProperty = GetRelatedEndPropertyValue(relationship, "NavigationProperty");
                            var identity = GetPropertyValue(navigationProperty, "Identity");

                            //get the IsLoaded property on entry
                            var isLoadedProperty = entry.Entity.GetType().GetProperty(identity + "IsLoaded");
                            if (isLoadedProperty != null)
                            {
                                isLoadedProperty.SetValue(entry.Entity, true, null);
                            }
                        }
                    }
                }
            }
        }

        private static object GetPropertyValue(object inputObject, string propertyName)
        {
            object result = null;

            if (inputObject != null)
            {
                var property = inputObject.GetType().GetProperty(propertyName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

                if (property != null)
                {
                    result = property.GetValue(inputObject, null);
                }
            }

            return result;
        }

        private static object GetRelatedEndPropertyValue(RelatedEnd inputObject, string propertyName)
        {
            object result = null;

            if (inputObject != null)
            {
                PropertyInfo property = null;

                property = inputObject.GetType().GetProperty(propertyName, BindingFlags.GetProperty | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

                if (property != null)
                {
                    result = property.GetValue(inputObject, null);
                }
            }

            return result;
        }

该解决方案有点让人失望，因为我必须访问密封属性“ NavigationProperty”，然后访问NavigationProperty.Identity才能获得正确的导航（例如，Person.Addresses而不是Person.Address）。希望将来会有更优雅的表现。

请注意，为了使其正常工作，我更新了Types T4模板以为我创建IsLoaded属性，例如，在Person上，我为Addresses创建了AddressesIsLoaded属性为：

<#
    if (navProperty.ToEndMember.RelationshipMultiplicity == RelationshipMultiplicity.Many)
        {
#>
    //The IsLoaded property for use on the client side when including collections
    [DataMember]
    <#=Accessibility.ForReadOnlyProperty(navProperty)#> bool <#=code.Escape(navProperty)#>IsLoaded
    {
        get; set;
    }
<#
        }
#>