查找导航属性的相关FK属性 [英] Finding the related FK property of a Navigation Property

问题描述

在运行时，我想查找一个EntityObject是否还有一个给定的NavigationProperty的外键属性。我下面有两个步骤。我想这将需要一些元数据查询。

At run time I would like to find whether an EntityObject also has a foreign key property for a given NavigationProperty. I have this in two steps below. I imagine this is going to require some metadata querying.

我不确定如何测试元数据类是否指向特定EntityObject类型的类型：即我在概念上知道但不是程式上的EntityType实例和EntityObject实例之间的关系。

I am unsure how to test whether a metadata class points to the type of a particular EntityObject type: ie I know conceptually but not programmically the relationship between an EntityType instance and an EntityObject instance.

到目前为止，我有：

    /*puesdo code class representing edm example*/
    class Possesion: EntityObject
    {

        //Nav prop
        public Person Owner { get; set; }

        //related FK prop
        public int OwnerId { get; set; }

    }

    public static NavigationProperty GetNavigationProperty<TObjectContext, T>(
        this ObjectContext context, 
        Expression<Func<T, Object>> targetProperty)
        where TObjectContext : ObjectContext
    {
        //eg: possession => possession.Owner  property type would be person
        PropertyInfo targetProp = GetPropertyType(targetProperty);
        //target type would be Possesion
        Type targetType = targetProp.DeclaringType;

        var containerName = context.DefaultContainerName;
        var model = DataSpace.CSpace;
        var workspace = context.MetadataWorkspace;
        var container = workspace.GetEntityContainer(containerName, model);

        EntitySetBase entitySet = container.BaseEntitySets
            .Where(e => e.Name == context.GetEntitySetNameFromType(targetType))
            .FirstOrDefault();

        if (entitySet == null)
            return null;

        //materialize nav props for testing
        var navigationProps = entitySet.ElementType.Members
            .Where(m => m.BuiltInTypeKind == BuiltInTypeKind.NavigationProperty
            )
            .Cast<NavigationProperty>()
            .ToList();

        //The question: how to filter the nav props for that which pertains 
        // to the target property?
        NavigationProperty navProp = navigationProps
            .Where(
            //how do we select the nav property based on the Passed EntityObject's type
            //ie how to we link the Metadata type to the concrete type??
            n => n.FromEndMember.TypeUsage.???????? == targetProp.PropertyType)
            .FirstOrDefault();


        return navProp;
    }

    public static String GetPossibleFKPropertyName(Type entityObjectType, NavigationProperty property)
    { 
        //Check each end for the target type
        //with this end ie To or From, determine if there is a Property on the entityObject that equated to the PropertyRef column
        //return this.

        var toEnd = property.ToEndMember.GetEntityType();
        //Again how do I determine that the Person metadata is a Person EntityObjectType?
        if (toEnd.SomeTypeMember???? == entityObjectType)
            return toEnd.KeyMembers[0].Name; //Testing HACK, return name for now.

        var fromEnd = property.FromEndMember.GetEntityType();
        if (fromEnd.SomeTypeMember???? == entityObjectType)
            return fromEnd.KeyMembers[0].Name;

        return "";

    }

推荐答案

简单地对ElementType的FullName进行文本比较

I ended up simply doing a text comparison on the FullName of the ElementType

ie：

n =>((RefType)n.ToEndMember.TypeUsage.EdmType).ElementType.FullName 
                               == targetProp.PropertyType.FullName)

还有ToEnd是我定位的属性，一旦我有NavigationProperty，调用 GetDependentProperties（）似乎产生FK属性名称之后我是：

also the ToEnd being the property I am targeting then once I had the NavigationProperty, calling GetDependentProperties() seems to yield what I am after being the FK property name ie:

    public static String GetFKPropertyName(this NavigationProperty property)
    { 
        var depProp = property.GetDependentProperties().FirstOrDefault();

        if (depProp == null)
            return "";

        return depProp.Name;

    }

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