I am using Entity Framework 4.1 (Code First) as O/R mapping framework:
I have three Entities: Post, PostForUser and User, whereas a PostForUser is associated with exactly one Post and one User.
Now I want to fetch all Posts for a given user and additionally load the user which created the post:
var posts = _dbContext.PostsForUser
.Include("Post.ByUser")
.Where(x => x.WasRead == false && x.User.Id == CurrentUser.Id)
.Select(x => x.Post)
.ToArray();
Using the query above, the "ByUser" property is never loaded. I am not using lazy loading at all, but I still can't get the loading working properly.
There aren't any custom mapping configs or special conventions registered. Just the following entity definitions:
public class Post
{
public int Id { get; set; }
public string Content { get; set; }
public DateTime Date { get; set; }
public User ByUser { get; set; }
}
public class PostForUser
{
public int Id { get; set; }
public User User { get; set; }
public Post Post { get; set; }
public bool WasRead { get; set; }
}
Your include .Include("Post.ByUser") applies to PostForUser but your are selecting Post so the the include should go to the and of the select:
var posts = _dbContext.PostsForUser
.Where(x => x.WasRead == false && x.User.Id == CurrentUser.Id)
.Select(x => x.Post).Include("ByUser")
.ToArray();
Related
public class User
{
[Key]
public int id { get; set; } //PK
public string emailAddress { get; set; }
public List<Task> tasks { get; set; }
}
public class Task
{
[Key]
public int id { get; set; } //PK
public string name { get; set; }
//Navigation Properties
public User user{ get; set; }
public int userId { get; set; }
}
I've got two models above configured following the MSDN tutorial. So how can I properly get the number of tasks associated with a user?
I tried context.users.Where(u => u.emailAddress == email).FirstOrDefaultAsync().tasks.count; but it gives me a null pointer reference on the tasks object.
Then I tried context.tasks.Where(o=>o.user.emailAddress==email).Count() gives me correct number so it works
so I am wondering why the List is a null reference instead of a list with some elements in? thanks for the advice
Try the following query:
var cnt = context.users
.Where(u => u.emailAddress == email)
.Select(u => u.tasks.Count())
.FirstOrDefault();
You have to use LINQ extension Count() instead of List.Count
I think you are using entity framework with Eager loading (description). In that case you should call explicitly Include() method to load all user tasks. Example:
await (context.users.Where(u => u.emailAddress == email).Include(u => u.Tasks).FirstOrDefaultAsync()).Tasks.Count();
UPD: Not for the Production
Here is a simplified version of my model:
public class User {
public int UserID { get; set; }
public string FirstName { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; }
}
public class Recipe {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
public virtual User User { get; set; }
}
I have a controller that I'd like to return a User as well as some summary information about their recipes. The scaffolded controller code looks like this:
var user = await _context.Users.SingleOrDefaultAsync(m => m.UserID == id);
It works fine. Now I try to add the Recipes, and it breaks:
var user = await _context.Users.Include(u => u.Recipes).SingleOrDefaultAsync(m => m.UserID == id);
My web browser starts to render the JSON, and it flickers and I get a message in the browser saying the connection has been reset.
My Theory - I believe that the parent (User) renders, which exposes the child (Recipe) which contains a reference to the parent (User), which contains a collection of the child (Recipe) and so on which is causing an infinite loop. Here's why I think this is happening:
The Visual Studio debugger allows me to navigate the properties in that way infinitely.
If I comment out the Recipe.User property, it works fine.
What I've tried
I tried to just include the data from Recipe that I need using Entity Framework projection (I'm attempting to not include Recipe.User). I tried to only include Recipe.RecipeName... but when I try to use projection to create an anonymous type like this:
var user = await _context.Users.Include(u => u.Recipes.Select(r => new { r.RecipeName })).SingleOrDefaultAsync(m => m.UserID == id);
I receive this error:
InvalidOperationException: The property expression 'u => {from Recipe r in u.Recipes select new <>f__AnonymousType1`1(RecipeName = [r].RecipeName)}' is not valid. The expression should represent a property access: 't => t.MyProperty'.
What is the solution? Can I project with different syntax? Am I going about this all wrong?
Consider using POCOs for serialization rather than doubly-linked entity classes:
public class UserPOCO {
public int UserID { get; set; }
public string FirstName { get; set; }
public ICollection<RecipePOCO> Recipes { get; set; }
}
public class RecipePOCO {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
}
Copy the entity contents to the corresponding POCO and then return those POCO objects as the JSON result. The removal of the User property via usage of the RecipePOCO class will remove the circular reference.
I can propose you 3 options.
U sing [JsonIgnore] on property, but it will work on every use of Recipe class, so when you would like to just return Recipe class you won't have User in it.
public class Recipe {
public int RecipeID { get; set; }
public string RecipeName { get; set; }
public int UserID { get; set; }
[JsonIgnore]
public virtual User User { get; set; }
}
You can this solution to stop reference loop in all jsons https://stackoverflow.com/a/42522643/3355459
Last option is to create class (ViewModel) that will only have properties that you want send to the browser, and map your result to it. It is propably best from security reason.
I am using Entity Framework Core following Chris Sakell's blog here.
He uses generics to manage his repositories and also a base repository that he uses for all the other repositories.
Part of the base repository has the the following code for the retrieval of a single entity that also downloads related entities using the includeProperties option. Here is the generic code for a retrieving a single item.
public T GetSingle(Expression<Func<T, bool>> predicate, params Expression<Func<T, object>>[] includeProperties)
{
IQueryable<T> query = _context.Set<T>();
foreach (var includeProperty in includeProperties)
{
query = query.Include(includeProperty);
}
return query.Where(predicate).FirstOrDefault();
}
I am using it on a client table that has many jobs attached to it.
This is how I structured my code.
public ClientDetailsViewModel GetClientDetails(int id)
{
Client _client = _clientRepository
.GetSingle(c => c.Id == id, c => c.Creator, c => c.Jobs, c => c.State);
if(_client != null)
{
ClientDetailsViewModel _clientDetailsVM = mapClientDetailsToVM(_client);
return _clientDetailsVM;
}
else
{
return null;
}
}
The line:
.GetSingle(c => c.Id == id, c => c.Creator, c => c.Jobs, c => c.State);
successfully retrieves values for creator state and job.
However, nothing is retrieved for those related entities associated with the "jobs".
In particuar, JobVisits is a collection of visits to jobs.
For completeness I am adding the "job" and "jobvisit" entities below
public class Job : IEntityBase
{
public int Id { get; set; }
public int? ClientId { get; set; }
public Client Client { get; set; }
public int? JobVisitId { get; set; }
public ICollection<JobVisit> JobVisits { get; set; }
public int? JobTypeId { get; set; }
public JobType JobType { get; set; }
public int? WarrantyStatusId { get; set; }
public WarrantyStatus WarrantyStatus { get; set; }
public int? StatusId { get; set; }
public Status Status { get; set; }
public int? BrandId { get; set; }
public Brand Brand { get; set; }
public int CreatorId { get; set; }
public User Creator { get; set; }
....
}
public class JobVisit : IEntityBase
{
...
public int? JobId { get; set; }
public Job Job { get; set; }
public int? JobVisitTypeId { get; set; }
public JobVisitType VisitType { get; set; }
}
My question is, how do I modify the repository code above and my GetSingle use so that I can also load the related enitities JobVisit collection and the other related single entities Brand and JobType?
It is intended that navigation properties are not necessary retrieved for associated with the "jobs". That is why some properties are null. By default the .Include(property); goes only 1-level deep and that is a good thing. It prevents your query from fetching all the data of your database.
If you want to include multiple levels, you should use .ThenInclude(property) after .Include(property). From the documentation:
using (var context = new BloggingContext())
{
var blogs = context.Blogs
.Include(blog => blog.Posts)
.ThenInclude(post => post.Author)
.ToList();
}
My advice is that your method public T GetSingle(...) is nice and I would not change it in order to include deeper levels. Instead of that, you can simply use explicit loading. From the documentation:
using (var context = new BloggingContext())
{
var blog = context.Blogs
.Single(b => b.BlogId == 1);
context.Entry(blog)
.Collection(b => b.Posts)
.Load();
context.Entry(blog)
.Reference(b => b.Owner)
.Load();
}
I use entity framework core 1.1.
I have a query like below, and I expect to users who have UserProfile by using Include, load UserProfile.
But this query always return UserProfile null .
Query:
var user = dbContext.UserMappers
.Where(e => e.OldUserId == id)
.Select(e => e.User)
.Include(e=>e.UserProfile)
.FirstOrDefault();
Models:
public class UserMapper
{
[Key, ForeignKey(nameof(User))]
public string UserId { get; set; }
public User User { get; set; }
public int OldUserId { get; set; }
}
public class User : IdentityUser
{
public bool Suspended { get; set; }
public string Nickname { get; set; }
public virtual UserProfile UserProfile { get; set; }
}
public class UserProfile
{
[Key, ForeignKey(nameof(User))]
public string UserId { get; set; }
public string Name { get; set; }
public string Family { get; set; }
public string Telephone { get; set; }
}
From the EF Core documentation - Loading Related Data - Ignored includes section (highlight is mine):
If you change the query so that it no longer returns instances of the entity type that the query began with, then the include operators are ignored.
This is different from EF6 where Include works on the final query entity type. I don't know if this is a current limitation or "by design", but for now you have to start your queries with the entity requiring includes.
In your case, it should be something like this:
var user = dbContext.Users
// if you don't have inverse navigation property
.Where(e => dbContext.UserMappers.Any(um => um.UserId == e.Id && um.OldUserId == id))
// if you have inverse collection navigation property
//.Where(e => e.UserMappers.Any(um.OldUserId == id))
// if you have inverse reference navigation property
//.Where(e => e.UserMapper.OldUserId == id)
.Include(e => e.UserProfile)
.FirstOrDefault();
I'm trying to setup a method that returns all presentations that are not overlapping with presentations you have signed up for. However, when trying to implement this I came across an error I can't seem to fix, I looked around and haven't been able to find any similar issues. Am I missing something obvious?
This is the Error:
InvalidOperationException: variable 't0' of type
'Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor+TransparentIdentifier`2[NameSpace.Models.Presentation,Microsoft.EntityFrameworkCore.Storage.ValueBuffer]'
referenced from scope '', but it is not defined
These are my models.
public class ApplicationUser : IdentityUser
{
public List<Presentation> MyPresentations { get; set; }
public List<PresentationUser> RegisteredPresentations { get; set; }
}
public class Presentation
{
public int PresentationId { get; set; }
public string HostId { get; set; }
public ApplicationUser Host { get; set; }
public List<PresentationUser> Attendees { get; set; }
public int TimeId { get; set; }
public PresentationTime Time { get; set; }
}
public class PresentationUser
{
public int PresentationId { get; set; }
public Presentation Presentation { get; set; }
public string ApplicationUserId { get; set; }
public ApplicationUser ApplicationUser { get; set; }
}
public class PresentationTime
{
public int PresentationTimeId { get; set; }
public DateTime StartTime { get; set; }
public DateTime EndTime { get; set; }
}
This is the method I can't get to work
private async Task<IQueryable<Presentation>> GetAvailablePresentations()
{
User user = await context.Users
.Include(u => u.RegisteredPresentations)
.ThenInclude(eu => eu.Presentation.Host)
.FirstOrDefaultAsync(u => u.Id == userManager.GetUserId(User));
var Presentations = context.Presentations
.Include(e => e.Host)
.Include(e => e.Time)
.Include(e => e.Attendees)
.ThenInclude(e => e.ApplicationUser)
// Filter Out Conditions
.Where(e => e.Attendees.All(u => u.ApplicationUserId != user.Id)) // Cannot see Presentations they are attending.
.Where(e => e.HostId != user.Id); // Cannot see their own Presentation
var debug = user.RegisteredPresentations.Select(ex => ex.Presentation).ToList();
// This section makes it so that users can't sign up for more that one Presentation per timeslot.
// Error Occurs Here
Presentations = Presentations.Where(e => debug.All(ex =>
ex.Time.EndTime < e.Time.StartTime || e.Time.EndTime < ex.Time.StartTime));
// This also does not work
// Presentations = Presentations.Where(e => debug.All(ex => ex.Time.StartTime != e.Time.StartTime));
return Presentations;
}
If anyone can help me fix this it would be huge help.
Note: I stripped a lot of other logic to help isolate this issue, so I may have a couple unnecessary .Include() in this code.
Presentations is not a list, it's still a IQueryable - a not-yet-executed query to DB. Applying Where you instruct EF to apply additional WHERE in SQL.
But debug is a list of objects in memory (.ToList()). How you think EF will transfer them back to DB?
If you want all filtering be applied in DB - you should change debug to list of something "simple" (list of ids?) - then EF will be able to pass this list back to DB.
Alternatively, you should read all suitable Presentations into memory (call .ToList()) and apply last filtering in memory. You may calculate min(StartTime) and max(EndTime) from debug and apply this two simple values to Presentations query (you will receive less unnecessary items) then read to memory and apply "strong" filtering in memory.