问题描述
对于我正在使用实体框架的项目，我希望能够枚举给定对象实例的所有导航属性(假设它是由 EF 生成的对象).从那里我想为每个导航属性获取相关的 Id 属性.
For a project I'm working with Entity Framework and I'd like to be able to enumerate all navigational properties for a given object instance (assuming it's an object generated by EF). From there I'd like to get the related Id property for every navigational property.
例如，如果我得到一个类 Person 的实例，我希望能够找到它的导航属性，称为 Address 和 Boss.对于这两个导航属性，我想查找"名为 AddressId 和 BossId 的相关 Id 属性.
For example, if I get an instance of the class Person, I want to be able to find it's navigational properties called Address and Boss. For those two navigational properties I want to then "lookup" the related Id properties called AddressId and BossId.
我需要这些 Id 属性，以便我可以在不同的数据库上运行查询，该数据库没有相同的外键但确实具有完全相同的 Id.
I need those Id properties so I can run queries on a different database which does not have the same foreign keys but does have exactly the same Ids.
到目前为止，我已经找到了一种方法来获取 RelationshipManager 用于 EF 生成的随机对象实例.在调试时，我可以通过 Manager 的 Relationships 属性获得外键关系.但我只能得到导航属性名称.所以我可以看到有一个 FK_Person_Address 与名为 Address 的导航属性相关，但我找不到 AddressId.
So far I have figured out a way to get the RelationshipManager for a random object instance generated by EF. And while debugging I can get to the foreign key relations via the Manager's Relationships property. But I can only get as far as the navigational property name. So I can see there's a FK_Person_Address which is related to the navigational property called Address but I can't find the AddressId.
所以我的问题是，我如何动态地(不了解 Person 类的布局)发现与 Address<相关的 AddressId 属性/代码>?
So my question is, how can I dynamically (with no knowledge of the Person class' layout) discover the AddressId property which is related to Address?
我知道外键关系可能在关系的另一端具有 Id 属性(Boss 指向 Person 而不是 Person 有一个 BossId).在这种情况下，我仍然希望在检查 Person 的实例时发现 Boss 有一个 PersonId.
I am aware the Foreign Key relationship might have the Id property on the other side of the relation (Boss pointing to Person in stead of Person having a BossId). In that case, I'd still like to discover that Boss has a PersonId when I'm inspecting an instance of Person.
推荐答案
这将为您提供一个字典，其中所有导航属性为 Key，所有相关属性为 Value(该值可能是来自其他实体的属性)
This will give you a dictionary with all navigation properties as Key and all related properties as Value (the value might be a property from the other entity)
将这些添加到您的 DBContext 类并调用 db.GetForeignKeyProperties
Add these to your DBContext class and call db.GetForeignKeyProperties<Person>()
结果会是这样的:
地址"-地址 ID"
老板"-Person.BossID"
"Boss" - "Person.BossID"
public Dictionary<string,string> GetForeignKeyProperties<DBType>()
{
EntityType table = GetTableEntityType<DBType>();
Dictionary<string, string> foreignKeys = new Dictionary<string, string>();
foreach (NavigationProperty np in table.NavigationProperties)
{
var association = (np.ToEndMember.DeclaringType as AssociationType);
var constraint = association.ReferentialConstraints.FirstOrDefault();
if (constraint != null && constraint.ToRole.GetEntityType() == table)
foreignKeys.Add(np.Name, constraint.ToProperties.First().Name);
if (constraint != null && constraint.FromRole.GetEntityType() == table)
foreignKeys.Add(np.Name, constraint.ToProperties.First().DeclaringType.Name+"."+constraint.ToProperties.First().Name);
}
return foreignKeys;
}
private EntityType GetTableEntityType<DBType>()
{
return GetTableEntityType(typeof(DBType));
}
private EntityType GetTableEntityType(Type DBType)
{
ObjectContext objContext = ((IObjectContextAdapter)this).ObjectContext;
MetadataWorkspace workspace = objContext.MetadataWorkspace;
EntityType table = workspace.GetEdmSpaceType((StructuralType)workspace.GetItem<EntityType>(DBType.FullName, DataSpace.OSpace)) as EntityType;
return table;
}
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