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
Related
I have a .net core api application which includes EF to retrieve data. I have set up a data context and I can map tables from the db fine. When I try and set up a relationship though I am always getting a null back for the nested object.
I have an 'Opportunity' class which contains an ICollection of 'Notes'
public class Opportunity
{
public int Id { get; set; }
public string Name { get; set; }
...
public decimal FinalDealProfit { get; set; }
public ICollection<CRMNote> CRMNotes { get; set; }
}
and a Note class that references the opportunity:
public class CRMNote
{
public int Id { get; set; }
public int OpportunityId { get; set; }
public string Note { get; set; }
public string User { get; set; }
public DateTime DateTime { get; set; }
public string FilePath { get; set; }
public Opportunity Opportunity { get; set; }
}
In my context class have the following set up:
modelBuilder.Entity<Opportunity>(entity =>
{
entity.ToTable("CRM_Opportunity");
entity.HasMany<CRMNote>(n => n.CRMNotes)
.WithOne(t => t.Opportunity)
.HasForeignKey(k => k.OpportunityId);
});
and I have also been mapping the Note class:
modelBuilder.Entity<CRMNote>(entity =>
{
entity.ToTable("CRM_Note");
//entity.HasOne<Opportunity>(t => t.Opportunity)
// .WithMany(p => p.CRMNotes)
// .HasForeignKey(k => k.OpportunityId);
});
as you can see I have been playing around with how to connect the entities together.
Whenever I retrieve the opportunity though the notes array is always null. I have tried putting an empty constructor on the Opportunity class:
public Opportunity()
{
CRMNotes = new List<CRMNote>();
}
but this just means I get an empty array rather than a null.
I can't see what I have missed. I have checked the docs for it:
https://www.entityframeworktutorial.net/efcore/one-to-many-conventions-entity-framework-core.aspx
but clearly I have missed something. Any help greatly appreciated as this should be an easy task but something is clearly eluding me.
There are three common O/RM patterns used to load related data
Eager loading,
Explicit loading
and
Lazy loading
For example, in eager loading you can use:
var opportunities=context.opportunities.Include(opportunity=>opportunity.CRMNotes).ToList()
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 have next entity
public class Objective
{
public virtual UserInfo AssignedUser { get; set; }
public int? AssignedUserID { get; set; }
public string ObjectiveText { get; set; }
public virtual ICollection<ObjectiveTask> Tasks { get; set; }
public virtual UserInfo User { get; set; }
public int UserID { get; set; }
}
One objective could has one Assigned User and one User but many Tasks.
After getting Entity from DB I map it to DTO class which looks like this
public class ObjectiveListViewModel
{
public string AssignedString { get; set; }
public string ObjectiveText { get; set; }
public int TasksCount { get; set; }
public string UserContactName { get; set; }
}
Mapping settings doesn't meter
When I do this with query like this
(from objective in context.Set<Objective>() select objective)
.Include(o => o.User)
.Include(o => o.AssignedUser)
.ToListAsync();
Everything works cool - User and Assigned User properties are loaded and no need do extra query to DB to get their data.
But I need return objectives with tasks amount.
To do this I've created a generic class
public class EntitySubCount<TEntity>
{
public TEntity Entity { get; set; }
public int GroupCount { get; set; }
}
And use it in this way
(from objective in context.Set<Objective>() select objective)
.Include(o => o.User)
.Include(o => o.AssignedUser)
.Select(o=> new EntitySubCount<Objective> {
Entity = o,
GroupCount = o.Tasks.Count })
.ToListAsync();
But User and Assigned User properties are not loaded and it require additional query to DB to get their data.
I understand that it because lazy loading.
The question is - how I can get from DB my Entity with loaded nav. properties and with count of Tasks at once?
Thank you for any help
You are close. No need for the includes if you are projecting. In this case I project to an anonymous type, but you could create a ViewModel class to project to if desired.
var objectiveList = context.Objectives
.Select(o => new
{
Entity = o,
// or you could just pick the properties:
ObjectiveText = o.ObjectiveText,
User = o.User,
AssignedUser = o.AssignedUser,
GroupCount = o.Tasks.Count
}).ToList();
EDIT: I see you already have a ViewModel(DTO). You might be looking for something like this:
var objectiveList = context.Objectives
.Select(o => new ObjectiveListViewModel
{
AssignedString = o.AssignedUser.Name,
ObjectiveText = o.ObjectiveText,
TasksCount = o.Tasks.Count
UserContactName = o.User.Name
}).ToList();
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 new to MVC and EF code first. I'm in struggle to model a real-estate company DB model using EF code-first approach and I did some exercises as well as reading some online tutorials.
First thing I have a customers table that would be in relation with one or more properties he/she has registered as it's owner to sell or to rent, I was wondering if it is possible to have some sub classes inside a model class for registered properties as below:
public Property
{
public int PropertyID { get; set; }
public bool IsforSale { get; set; }
public bool IsforRent { get; set; }
public class Apartment{
public int ApartmentID { get; set; }
public int AptSqureMeter { get; set; }
. . .
. . .
}
public class Villa{
public int VillaID { get; set; }
public int VillaSqureMeter { get; set; }
. . .
. . .
}
and also other sub-classes for other types of properties
}
If the answer is Yes, then how should I declare the relations using data annotation or Fluent API, and then please help me how to update both Customers table and Property table with the customer information and property info at the same time?
thanks for your answer in advance.
As #Esteban already provided you with a pretty detailed answer on how to design your POCOs and manage the relationship between them, I will only focus on that part of your question:
how should I declare the relations using data annotation or Fluent API
First of all, you should know that certain model configurations can only be done using the fluent API, here's a non exhaustive list:
The precision of a DateTime property
The precision and scale of numeric properties
A String or Binary property as fixed-length
A String property as non-unicode
The on-delete behavior of relationships
Advanced mapping strategies
That said, I'm not telling you to use Fluent API instead of Data Annotation :-)
As you seem to work on an MVC application, you should keep in mind that Data Annotation attributes will be understood and processed by both by Entity Framework and by MVC for validation purposes. But MVC won't understand the Fluent API configuration!
Both your Villa and Apartment classes have similar properties, if they are the same but as it's type, you could create an enum for that.
public enum PropertyType {
Apartment = 1,
Villa
}
public class Property {
public int PropertyID { get; set; }
public bool IsforSale { get; set; }
public bool IsforRent { get; set; }
public PropertyType PropertyType { get; set; }
public int SquareMeter { get; set; }
}
This way of modelating objects is refered as plain old clr object or POCO for short.
Assume this model:
public class User {
public int UserId { get; set; }
public string Username { get; set; }
public virtual List<Role> Roles { get; set; }
}
public class Role {
public int RoleId { get; set; }
public string Name { get; set; }
public virtual List<User> Users { get; set; }
}
Creating relations with fluent api:
Mapping many to many
On your OnModelCreating method (you'll get this virtual method when deriving from DbContext):
protected override void OnModelCreating(DbModelBuilder builder) {
// Map models/table
builder.Entity<User>().ToTable("Users");
builder.Entity<Role>().ToTable("Roles");
// Map properties/columns
builder.Entity<User>().Property(q => q.UserId).HasColumnName("UserId");
builder.Entity<User>().Property(q => q.Username).HasColumnName("Username");
builder.Entity<Role>().Property(q => q.RoleId).HasColumnName("RoleId");
builder.Entity<Role>().Property(q => q.Name).HasColumnName("Name");
// Map primary keys
builder.Entity<User>().HasKey(q => q.UserId);
builder.Entity<Role>().HasKey(q => q.RoleId);
// Map foreign keys/navigation properties
// in this case is a many to many relationship
modelBuilder.Entity<User>()
.HasMany(q => q.Roles)
.WithMany(q => q.Users)
.Map(
q => {
q.ToTable("UserRoles");
q.MapLeftKey("UserId");
q.MapRightKey("RoleId");
});
Mapping different types of relationships with fluent api:
One to zero or one:
Given this model:
public class MenuItem {
public int MenuItemId { get; set; }
public string Name { get; set; }
public int? ParentMenuItemId { get; set; }
public MenuItem ParentMenuItem { get; set; }
}
And you want to express this relationship, you could do this inside your OnModelCreating method:
builder.Entity<MenuItem>()
.HasOptional(q => q.ParentMenuItem)
.WithMany()
.HasForeignKey(q => q.ParentMenuItemId);
One to many
Given this model:
public class Country {
public int CountryId { get; set; }
public string Name { get; set; }
public virtual List<Province> Provinces { get; set; }
}
public class Province {
public int ProvinceId { get; set; }
public string Name { get; set; }
public int CountryId { get; set; }
public Country Country { get; set; }
}
You now might want to express this almost obvious relationship. You could to as follows:
builder.Entity<Province>()
.HasRequired(q => q.Country)
.WithMany(q => q.Provinces)
.HasForeignKey(q => q.CountryId);
Here are two useful links from MSDN for further info:
Configuring Relationships with the Fluent API.
Code First Relationships Fluent API.
EDIT:
I forgot to mention how to create a many to many relationship with additional properties, in this case EF will NOT handle the creation of the join table.
Given this model:
public class User {
public int UserId { get; set; }
public string Username { get; set; }
public virtual List<Role> Roles { get; set; }
pubilc virtual List<UserEmail> UserEmails { get; set; }
}
pubilc class Email {
public int EmailId { get; set; }
public string Address { get; set; }
public List<UserEmail> UserEmails { get; set; }
}
public class UserEmail {
public int UserId { get; set; }
public int EmailId { get; set; }
public bool IsPrimary { get; set; }
public User User { get; set; }
public Email Email { get; set; }
}
Now that we've added a new property into our join table ef will not handle this new table.
We can achieve this using the fluent api in this case:
builder.Entity<UserEmail>()
.HasKey( q => new {
q.UserId, q.EmailId
});
builder.Entity<UserEmail>()
.HasRequired(q => q.User)
.WithMany(q => q.UserEmails)
.HasForeignKey(q => q.EmailId);
builder.Entity<UserEmail>()
.HasRequired(q => q.Email)
.WithMany(q => q.UserEmails)
.HasForeignKey(q => q.UserId);