使用Linq返回EF6中的相关实体

Question

I am having a problem understanding how Linq and EF are working to return data. I have three simple classes

Products, Materials, Documents

Products are made up of materials and materials have documents. When I load a product, I want to return all the documents for the materials that product is made up from.

Here are my classes:

    public class Product
    {        
      public int Id { get; set; }
      public string Name { get; set; }
      ...
      public ICollection<ProductMaterials> ProductMaterial { get; set; }
    }
    public class ProductMaterials 
    {           
        public int Id { get; set; }

        public int ProductId { get; set; }
        public Product Product { get; set; }
        public int MaterialId { get; set; }
        public Materials Material { get; set; }
        ...           
    }

public class Document
{
    public int Id { get; set; }
    public string Name { get; set; }
    ...
    public ICollection<MaterialDocument> MaterialDocument { get; set; } 
}

public class MaterialDocument
{
    public int Id { get; set; }
    public int MaterialId { get; set; }
    public Materials Material { get; set; }
    public int DocumentId { get; set; }
    public Document Document { get; set; }
}

I am not having any issues when loading a material and its related documents. I use this query:

var materialDocuments = db.MaterialDocuments
                                     .Include("Document")
                                     .Where(i => i.MaterialId == id)
                                     .ToList();

How can I load Product with related Materials and the Material's documents? Do I need additional Navigation properties on the MaterialDocument class pointing back to ProductMaterials?

Answer 1

To return all of the Document records for a specific Product that you're loading (given an ID we'll call myProductID ), just do the following:

var product = db.Products.Find(myProductID); //The product that you're loading
var documents = product.ProductMaterials.SelectMany(pm => 
                         pm.Material.SelectMany(mat => 
                            mat.MaterialDocuments.Select(matdoc => matdoc.Document)));