如何在子集合上使用 where 条件创建分层查询

Question

I have this SQL query:

SELECT * 
FROM Orders o 
INNER JOIN OrderItems i on o.Id = i.OrderId
WHERE i.SomeFlag = 0

How do I turn this SQL into an EF hierarchical query that would return Orders with the OrderItems as child collection?

IMPORTANT: Notice the where condition on OrderItems!

EF Model is as follows:

class Order 
{
   public int Id { get; set; }
   public List<OrderItem> OrderItems { get; set; }
}
class OrderItem {
   public int OrderId { get; set; }
   public int ProductId { get; set; }
   public bool SomeFlag { get; set; }
   public Order Order { get; set; }
}

class MyDbContext : DbContext 
{
    public DbSet<Order> Orders { get; set; }
    public DbSet<OrderItems> OrderItems { get; set; }
}

The query must return IQueryable<T> where T cannot not be flat structure. It must be a hierarchy just like Order/OrderItem

Answer 1

Your Order & OrderItem classes should be look like:

class Order 
{
  public int Id { get; set; }

  // Navigation property  
  public IColection<OrderItem> OrderItems { get; set; }
}

class OrderItem
{
  public int Id { get; set; }
  public int OrderId { get; set; }

  // Navigation property  
  public Order Order { get; set; }
}

class MyDbContext : DbContext 
{
  ...

  public DbSet<Order> Orders { get; set; }
  public DbSet<OrderItem> OrderItems { get; set; }
}

For Query:

_context.Orders.Include(x => x.OrderItems).Where(x => x.OrderItems.Any(q => q.SomeFlag));

Now you have all orders with all order items for each one with true value for SomeFlag property.

In EF5 and above you can use Filtered Include such as:

_context.Orders.Include(x => x.OrderItems.Where(x => x.SomeFlag));