I'm a complete noob to Fluent NHibernate, and I'm using the Query Object Pattern based on a recommendation. Which I'm also new to. I'll try to keep the code samples concise and helpful.
User class:
public class User {
public Guid ID { get; set; }
public string Name { get; set; }
}
Visibility:
public enum VisibilityType {
Anybody,
OwnersOnly,
Nobody
}
Car class:
public class Car {
public Guid ID { get; set; }
public VisibilityType Visibility { get; set; }
public ICollection<User> Owners { get; set; }
}
So I need to write a conditional restriction method for the query object. Return all cars that have VisibilityType.Public, but if a car has Visibility property value of VisibilityType.OwnersOnly, restrict the return to users who belong to that group.
Here's the current restriction method that I have working, but without the condition:
public class CarQueryObject
{
private User user { get; set; }
private const string OwnersProperty = "Owners";
private const string OwnersIDProperty = "Owners.ID";
public CarQueryObject RestrictToOwners()
{
// How do I add a conditional criteria here? Only restrict by owner
// if the QueryObject has VisibilityType.OwnersOnly? Note that it should
// *NOT* restrict VisibilityType.Anybody
CreateOwnersAlias();
Criteria.Add(Restrictions.Eq(OwnersIDProperty, user.Id));
return this;
}
public CarQueryObject JoinFetchOwned()
{
Criteria.SetFetchMode(OwnersProperty, FetchMode.Join);
return this;
}
public void CreateOwnersAlias()
{
Criteria.CreateAlias(OwnersProperty, OwnersProperty, JoinType.LeftOuterJoin);
JoinFetchOwned();
}
}
?_?
an idea to get shown cars
var carsShown = session.CreateCriteria<Car>()
.JoinAlias("Owner", "owner")
.Add(Expressions.Or(
Expression.Eq("Visibility", Visibility.Anybody),
Expression.Eq("Visibility", Visibility.OwnersOnly) && Expression.Eq("owner.Id", currentUser.Id)
))
.List<Car>();
Related
public class Product
{
public int Id{get;set;}
public int UserId{get;set;}
public Users User{get;set;}
}
I have set the Users to Product's relative:
b.HasOne("User").WithMany().HasForeignKey("UserID");
When I use entityframework to get the list of products.
The User is returned null, why?
There is a value in User table and the UserId is right in Product Table.
var list = _context.Products.AsQueryable();
the items in list has the User=null.
You need to Include the entity you're looking for. For example, let's suppose I have the following context.
AppDbContext.cs
public class AppDbContext : DbContext
{
public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
{
}
public DbSet<Notification> Notifications { get; set; }
public DbSet<Offer> Offers { get; set; }
}
Notification.cs
public class Notification
{
public int Id { get; set; }
public string Title { get; set; }
public int? OfferId { get; set; }
public virtual Offer Offer { get; set; }
}
If you want to use the Offer entity from Notification, you need to use the following statement:
context.Notifications.Include(n=> n.Offers).ToList();
// Your code goes here
In your situation:
var list = _context.Products.Include(p=> p.User).AsQueryable();
You have to explicitly ask to include the users in the returned list.
_context.Products.Include(p => p.Users).AsQueryable();
I'm working with two different aggregate roots: Post and Question. Both of them have a Category.
So far I have implemented it as a shared entity (which I'm not sure if is a correct design in DDD).
public class Post
{
public Guid Id { get; private set; }
public Category Category { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
}
public class Question
{
public Guid Id { get; private set; }
public Category Category { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
}
public class Category
{
public int Id { get; private set; }
public string Name { get; private set; }
public string Key { get; private set; }
}
Note: I'm aware I'm falling into primitive obsession anti-pattern, and I have plans on refactor the primitives into ValueObjects.
After read this post DDD: Share entity with multiple aggregate roots I'm thinking that maybe I should convert the Category in a ValueObject (with multiple fields).
In theory Category could be an Entity with its own lifecycle, but reality is that I don't really add/remove/update categories.
Is it possible to use a shared Entity on DDD? Or I better rather use a ValueObject?
Lets deal with one aggregate first: Post
Now to answer your question:
Is it possible to use a shared Entity on DDD? Or I better rather use a ValueObject?
It depends on what you will do with Category.
Scenario 1:
You have a feature(or page) in your application to show all posts of a category. I would go with the following design:
public class Category
{
public int Id { get; set; }
//this is my in-memory database. Use repository and service to adjust yours
public static List<Post> Posts;
public Category()
{
Posts = new List<Post>();
}
public void AddPost(Guid id, string title, string body)
{
var post = new Post(id, title, body, this.Id);
//saving the post into in-memory. Perhaps you can check some business logic inside Post entity
Posts.Add(post);
}
// You can retrieve all posts of a single category
public IEnumerable<Post> GetAllPosts()
{
return Posts.Where(x => x.CategoryId == this.Id);
}
}
public class Post
{
public Guid Id { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
public int CategoryId { get; private set; }
public Post(Guid id)
{
Id = id;
}
public Post(Guid id, string title, string body, int categoryId)
{
//I prefer to pass guid into domain from external services.
//Using this way, your service will have the id to return to upper layers.
//Alternatively you can create new guid here on your own
Id = id;
Title = title;
Body = body;
CategoryId = categoryId;
}
// you can retrieve a post detail
public Post GetPost()
{
return Category.Posts.FirstOrDefault(x => x.Id == this.Id);
}
}
I can see only one aggregate root in this scenario: Category.
Scenario 2:
You have posts page, from there users can view detail post. Additionally, every post has a category which will be shown somewhere on that detailed page. You can have following simple design:
public class Post
{
public Guid Id { get; private set; }
public string Title { get; private set; }
public string Body { get; private set; }
public string CatKey { get; private set; }
public Post(Guid id)
{
Id = id;
}
public Post(Guid id, string title, string body, string catKey)
{
//I prefer to pass guid into domain from external services.
//Using this way, your service will have the id to return to upper layers.
//Alternatively you can create new guid here on your own
Id = id;
Title = title;
Body = body;
//I don't even bother with category id. This is a simple value object, you can store all of your categories
//into a hashtable of key-value
CatKey = catKey;
}
// you can retrieve a post detail
public Post GetPost()
{
//get your post detail from repo
}
}
Hope you can make your decision now.
The main question of Entity vs ValueObject is would two instances of the Category with the same values need to be tracked differently? The classic example is a dollar bill - in most instances, the serial number (ID) doesn't matter, and one dollar is the same as another (ValueObject). If your domain is collecting rare bills, though, that would change.
I'd suspect not in your case, since it appears Category is really just comprised of the name and key. If the Category of a Post changes, do you need to track what the Category previous was?
Let's say we have a document like this
public class Event
{
public string Id { get; set; }
public EntityDescriptor Venue { get; set; }
// Other properties omitted for simplicity
}
public class EntityDescriptor
{
public string Id { get; set; }
public string Name { get; set; }
}
And an index like this
public class Events : AbstractIndexCreationTask<Event>
{
public Events()
{
Map = items => from e in items
select new
{
Venue_Id = e.Venue.Id,
Venue_Name = e.Venue.Name
};
}
}
When trying to sort on Event.Venue.Id
session.Query<Event, Events>().Take(10).OrderBy(e => e.Venue.Id).ToArray();
the sent request is
/indexes/Events?&pageSize=10&sort=__document_id&SortHint-__document_id=String
Is this by design or a bug?
PS: OrderBy(e => e.Venue.Name) works as expected (sort=Venue_Name).
It's not a bug. __document_id is the special known field containing the ID of the document. It's there regardless of whether you have an .Id property.
edit
I misread your question. This indeed appears to be a bug. I recommend you send a simple repro case to the Raven forum and let them know which RavenDB version you're using.
public class PersonBrief
{
public int Id { get; set; }
public string Picture { get; set; }
public PersonBrief(Person person)
{
Id = person.Id;
Picture = person.Picture;
}
}
public class Person : PersonBrief
{
public string FullName { get; set; }
}
var results = session.Query<Person>()
.Select(x => new PersonBrief(x))
.ToList();
Assert.IsNull(results[0] as Person); // Fails
Is this a bug? If not, what would be the correct way to select only the fields i'm interested in?
It would work if you move the .ToList before the .Select, but that would be doing the work on the client.
If you want to do it on the server, you need to use As in your query, and you need a static index that does a TransformResults. See these docs.
I am using the Specification pattern, and have a working implementation (taken from the WhoCanHelpMe Codeplex project) for getting data via NLinq, generic repositories and all that goodness.
The root method is:
public IList<Case> GetCasesByUsername(string username)
{
CaseByUserNameSpecification spc = new CaseByUserNameSpecification(username);
return this.caseRepository.FindAll(spc).ToList();
}
The FindAll() method does the following:
public IQueryable<T> FindAll(ILinqSpecification<T, T> specification)
{
return specification.SatisfyingElementsFrom(this.Session.Linq<T>());
}
And, SatisfyingElementsFrom() does this:
public virtual IQueryable<TResult> SatisfyingElementsFrom(IQueryable<T> candidates)
{
if (this.MatchingCriteria != null)
{
return candidates.Where(this.MatchingCriteria).ToList().ConvertAll(this.ResultMap).AsQueryable();
}
return candidates.ToList().ConvertAll(this.ResultMap).AsQueryable();
}
So, for querying cases by CaseNb property of a Case, it's pretty straight-forward. A Specification like the one below works for me and gets the cases I'd want.
public class CaseByCaseNbSpecification : QuerySpecification<User>
{
private string caseNb;
public CaseByCaseNbSpecification(string caseNb)
{
this.caseNb = caseNb;
}
public string UserName
{
get { return this.caseNb; }
}
public override Expression<Func<Case, bool>> MatchingCriteria
{
get { return u => u.CaseNb.Equals(this.caseNb, StringComparison.CurrentCultureIgnoreCase); }
}
}
However, I am at a loss to understand how to do this when crossing multiple entities. What I'd like to have is a Specification that allows me to get Cases by UserName. Basically, in the database, there are three tables and these have been carried into entities. Here's are entities:
Here's the Case class:
public class Case : Entity
{
private ICollection<CaseUser> caseUsers = new HashSet<CaseUser>();
public virtual Patient Patient { get; set; }
public virtual string CaseNb { get; set; }
...
public virtual IEnumerable<CaseUser> CaseUsers { get { return caseUsers; } }
}
Here's the CaseUser:
public class CaseUser : Entity
{
public virtual Case Case { get; set; }
public virtual User User { get; set; }
...
}
And, User:
public class User : Entity
{
private ICollection<CaseUser> caseUsers = new HashSet<CaseUser>();
public virtual Account Account { get; set; }
public virtual string UserName { get; set; }
...
public virtual IEnumerable<CaseUser> CaseUsers { get { return caseUsers; } }
}
How would I write the Expression to get the data across the association table?
I believe your specification implementation should look something like this:
public class CaseByUsernameSpecification : QuerySpecification<Case>
{
private string userName;
public CaseByUsernameSpecification(string userName)
{
this.userName = userName;
}
public string UserName
{
get { return this.userName; }
}
public override Expression<Func<Case, bool>> MatchingCriteria
{
get { return c => c.CaseUsers.Any(cu => cu.User.Username == this.userName); }
}
}