实体框架 - 在子实体条件下过滤和检索子实体

Question

My problem is as follows: I have a Product entity which looks like this:

public int Id { get; set; }
public string Title { get; set; }
public decimal Price { get; set; }
public string Excerpt { get; set; }
public string Description { get; set; }
public virtual Category Category { get; set; }
public DateTime Published { get; set; }
public string[] Tags { get; set; }
public int PublisherId { get; set; }
public virtual User Publisher { get; set; }
public virtual ICollection<MyImage> Images { get; set; }

Now this Product entity can have many Images (as a child entity) which looks as follows:

public int Id { get; set; }
public string Description { get; set; }
public DateTime DateAdded { get; set; }
public bool IsMain { get; set; }
public byte[] Image { get; set; }
public virtual Product Product { get; set; }
public int ProductId { get; set; }

So, I've got a controller route, where I would like to retrieve all the products and only those images, which are main product images (most of the time, it's going to be only a single image, but I still prefer to return a list of them).

Currently, what I am trying to do, does not work:

public async Task<PagedList<Product>> GetProducts(UserParams userParams)
{
     var productsFromRepo = context.Products
         .Select(p => new {
             Product = p,
             Images = p.Images.Where(i => i.IsMain)
         })
         .OrderByDescending(b => b.Product.Published);

     var productsToReturn = productsFromRepo.Select(i => i.Product).AsQueryable();
     return await PagedList<Product>.CreateAsync(productsToReturn, userParams.PageNumber, userParams.PageSize);
}

I try to get all products, and their main image. And return a product with it's main image, and not all images. As you can see, I am returning a PagedList object, where I need to pass an IQueryable as first parameter of CreateAsync method.

The thing is, I managed to do the filtering on my anonymously projected object ( productsFromRepo ). But I can not figure out how to return that anonymous object as product object with filtered Images list.

It's always returning all images, not filtered how I need.

In this problem, I must have my lastly projected object, in this case productsToReturn to be an IQueryable object.

In my project, I am using lazy loading. So all child entities are lazy loaded by default.

So basically, what I get now is:

[
    {
        "id": 2,
        "title": "My First Product",
        "description": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.",
        "category": "Uncategorized",
        "price": 15.0,
        "excerpt": "Lorem ipsum",
        "tags": [
            "Tag1",
            "Tag2"
        ],
        "images": [
            {
                "id": 1,
                "description": "test",
                "isMain": true,
                "dateAdded": "2020-07-15T22:40:09.285481",
                "image":"/9j/...."
            },
            {
                "id": 2,
                "description": "test1",
                "isMain": false,
                "dateAdded": "2020-07-15T23:15:44.74166",
                "image":"/9j/...."
            },
            {
                "id": 3,
                "description": "test1",
                "isMain": false,
                "dateAdded": "2020-07-15T23:27:39.636685",
                "image":"/9j/...."
            }
        ],
        "published": "2020-07-15T22:39:27.89482",
        "publisher": {
            "id": 1,
            "name": null,
            "lastName": null,
            "email": "testemail@gmail.com"
        }
    }
]

And what i need is:

[
    {
        "id": 2,
        "title": "My First Product",
        "description": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.",
        "category": "Uncategorized",
        "price": 15.0,
        "excerpt": "Lorem ipsum",
        "tags": [
            "Tag1",
            "Tag2"
        ],
        "images": [
            {
                "id": 1,
                "description": "test",
                "isMain": true,
                "dateAdded": "2020-07-15T22:40:09.285481",
                "image":"/9j/...."
            },
        ],
        "published": "2020-07-15T22:39:27.89482",
        "publisher": {
            "id": 1,
            "name": null,
            "lastName": null,
            "email": "testemail@gmail.com"
        }
    }
]

Thanks in advance

Answer 1

Instead of selecting on products, try selecting on the images:

public async Task<PagedList<Product>> GetProducts(UserParams userParams)
{
     var productsFromRepo = context.Images
         .Where(i => i.IsMain)
         .Select(i => new Product {
             Id = i.Product.Id,
             Title = i.Product.Title,
             ...
             Images = new List<Image>{ i }
         })
         .OrderByDescending(b => b.Published)
         .AsQuerable();

     return await PagedList<Product>.CreateAsync(productsFromRepo, userParams.PageNumber, userParams.PageSize);
}

Answer 2

Well, the anonymous object doesn't help in my opinion. You can either filter the product's pictures after you retrieve it from the database, or use Query Filter if you want to stop EF from bringing it from the database.

Check this documentation to get a clear picture.

The idea is that you include the query filter in the fluent api configuration of the pictures entity:

builder.HasQueryFilter(p => p.IsMain);

This will stop EF from retrieving the pictures that aren't set as main, in ALL cases by default . If you want EF to retrieve all pictures (ie in pictures index) you have to use

.IgnoreQueryFilters()

in your query.

PS I didn't include the full code snippets, if it doesn't make sense to you, ask me to demonstrate the full code.