在没有关系的情况下针对EF上下文创建LINQ语句

Question

I cannot wrap my head around how to write a linq query against my EF context to get what I want.

1) What I have Database with no foreign keys assigned, and a reverse engineered code first entity framework project. I tried manually adding virtual classes so EF might create implied foreign keys in the DBcontext, but I get errors on my .Include statements still.

Without the include the only thing I can think of is to use left joins, but I haven't gotten it down yet. In the end there will be 21 tables I have to get data from, but the following table outline encapsulates the majority of issues i'm facing.

Sample data structure:

Table Human : HumanId, LastFoodEatenId, FavoriteFoodId, CurrentlyDesiredFoodId

Table Food : FoodId, FoodName, FoodStuff

Table Toys : HumanOwnerId, ToyId, ToyName

Table Pets : HumanOwnerId, PetId, PetName, PetType

Table PetSurgery : PetId, SurgeryId, SurgeryPerformed

2) What I want Given a HumanID, I want a compsite class or something like it from a single query.

Public Class QueryResult
{
  public Human human {get;set;}
  public Food LastEatenFood {get;set;}
  public Food FavoriteFood {get;set;}
  public Food CurrentlyDesiredFood {get;set;}
  public IEnumerable<Toy> Toys {get;set;}
  public IEnumerable<Pet> Pets {get;set;} //Includes surgeries if any
}

Is it even possible to write a single query to get this kind of information in a single db hit? I'd be fine is someone simply confirmed it is't possible. Then I can at least request we add relationships to our database.

Thanks in advance,

Answer 1

You can use linq to query multiple, non-related tables.

I'm going to assume a LOT about your entities, but here we go...

int humanId = 1234;

using (var context = new MyContext())
{
    var human = (from h in context.Humans
                 join lf in context.Foods on h.LastFoodEatenId equals lf.foodId into lfg
                 from lf in lfg.DefaultIfEmpty() // left join
                 join ff in context.Foods on h.FavoriteFoodId equals lf.foodId into ffg
                 from ff in ffg.DefaultIfEmpty() // left join
                 join cf in context.Foods on h.CurrentlyDesiredFoodId equals lf.foodId into cfg
                 from cf in cfg.DefaultIfEmpty() // left join
                 join p in context.Pets on h.humanId equals p.humanId into pg // group
                 join t in context.Toys on h.humanId equals t.humanId into tg // group
                 where h.humanId = humanId
                 select new QueryResult { human = h, LastEatenFood = lf, FavoriteFood = ff, CurrentlyDesiredFood = cf, Toys = tg, Pets = pg }
                 ).SingleOrDefault();
}

Note: I'm doing this from memory without a syntax checker, so ymmv. Adding surgeries should be possible as well, but may require a subquery.

Answer 2

I tried manually adding virtual classes

I assume you mean virtual collections . You can define relationships in a "code-first" model if they are not in the database. The only condition is that foreign keys must refer to properties that EF knows as primary keys. So you should be able to do LINQ queries using navigation properties in stead of these verbose joins by a model like this (reduced to the essentials):

class Human
{
    public int HumanId { get; set; }

    public int LastFoodEatenId { get; set; }
    public virtual Food LastEatenFood { get; set; }

    public int FavoriteFoodId { get; set; }
    public virtual Food FavoriteFood { get; set; }

    public int CurrentlyDesiredFoodId { get; set; }
    public virtual Food CurrentlyDesiredFood { get; set; }

    public virtual ICollection<Toy> Toys { get; set; }
    public virtual ICollection<Pet> Pets { get; set; }
}

class Food
{
    public int FoodId { get; set; }
}

class Pet
{
    public int PetId { get; set; }
    public int HumanOwnerId { get; set; }
}

class Toy
{
    public int ToyId { get; set; }
    public int HumanOwnerId { get; set; }
}

And a mapping:

class HumanMapping : EntityTypeConfiguration<Human>
{
    public HumanMapping()
    {
        HasOptional(h => h.LastEatenFood).WithMany()
            .HasForeignKey(h => h.LastFoodEatenId);
        HasOptional(h => h.FavoriteFood).WithMany()
            .HasForeignKey(h => h.FavoriteFoodId);
        HasOptional(h => h.CurrentlyDesiredFood).WithMany()
            .HasForeignKey(h => h.CurrentlyDesiredFoodId);
        HasMany(h => h.Toys).WithOptional().HasForeignKey(t => t.HumanOwnerId);
        HasMany(h => h.Pets).WithOptional().HasForeignKey(t => t.HumanOwnerId);
    }
}

EF will infer the primary keys by name conventions.

Now you will be able to execute a LINQ statement like:

context.Humans.Where(h => h.HumanId == id)
       .Include(h => h.LastEatenFood)
       .Include(h => h.FavoriteFood)
       .Include(h => h.CurrentlyDesiredFood)
       .Include(h => h.Toys)
       .Include(h => h.Pets)

From your description I understand that PetSurgery should be a junction class between Pet and another class ( Surgery ?). Anyway, I think you will manage creating the correct mappings, seeing this example.