应用包括基于ThenInclude的Lambda表达式字典

Question

我有几个实体框架7（核心）的实体：

public class Person { 
    public virtual Address Address { get; set; } 
    public virtual ICollection<Hobby> Hobbies { get; set; } 
} 

public class Address { 
    public String Street { get; set; } 
    public virtual Country Country { get; set; } 
} 

而且我有一个字符串数组如下：

String[] entities = new String[] { "Hobbies", "Address.Country" } 

鉴于此字符串数组我：

context.Persons 
    .Include(x => x.Hobbies) 
    .Include(x => x.Address).ThenInclude(x => x.Country); 

在EF6我可以这样做：

context.Persons.Include(entities[0]).Include(entities[1]); 

但是在EF7 Include中不允许字符串。我创建了词典：

private readonly Dictionary<String, LambdaExpression> _properties = new Dictionary<String, LambdaExpression>(); 

这将是这样的：

x => x.Hobbies is for "Hobbies" 
x => x.Address.Country is for "Address.Country"  

和我有扩展名：

public static IQueryable<T> Include<T>(this IQueryable<T> source, Dictionary<String, LambdaExpression> properties) { 
} 

，我需要给出的解释适用于以下内容：

1. Fo R “X => x.Hobbies” 只是做：

   source.Include(x => x.Hobbies); 
   

2. 如果表达式是像 “X => x.Address.Country” 补充：

   source.Include(x => x.Address).ThenInclude(x => x.Country); 
   

可以这样做完了？

Answer 1

不确定ThenInclude()和EF 7，但你可以做你的存储库这样的事情（使用EF 6测试）：

public MyEntity GetMyEntity_EagerlyLoad(DbContext context, int id, params Expression<Func<MyEntity, object>>[] propertiesToLoad) 
{ 
    var q = context.MyEntities.Where(m => m.ID == id); 

    foreach (var prop in propertiesToLoad) 
     q = q.Include(prop); 

    return q.SingleOrDefault(); 
} 

然后你可以这样调用：

repo.GetMyEntity_EagerlyLoad(context, id, m => m.Property1, m => m.Property2, m => m.Property1.NestedProperty) 

编辑：还有另一种方法来使用投影进行EF加载。你可以做一个通用的存储库方法是这样的：

public MyEntity GetMyEntity_EagerlyLoad<T>(DbContext context, int id, Expression<Func<MyEntity, T>> loadingProjection, Func<T, MyEntity> resultProjection) 
{ 
    var q = context.MyEntities.Where(m => m.ID == id); 

    return q.Select(loadingProjection).AsEnumerable().Select(resultProjection).SingleOrDefault(); 
} 

然后用你想装的属性，并且希望该方法返回的实体称之为：

repo.GetMyEntity_EagerlyLoad(context, id, m => new { myEntity = m, m.Property1, m.Property2, m.Property1.NestedProperty }, m => m.myEntity)