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()
Related
I'm having difficult configuring a 1:1 mapping in EntityFrameworkCore using FluentAPI. The navigational reference is always NULL. The only obvious difference between my code and countless others I have examined is I am trying to map via composite keys.
I've played around using annotations instead of Fluent API but encounter the same issue described in my summary.
Class Definitions
[Table("SomeTable")]
public class Defect
{
[Column("Record")]
public int DefectId { get; set; }
[Column("insp_id")]
public int InspId { get; set; }
[Column("defectnum")]
public int Number { get; set; }
public virtual Simulation Simulation { get; set; }
}
[Table("SomeSimulationTable")]
public class Simulation
{
[Column("Record"), Key]
public int SimTableId { get; set; }
[Column("insp_id")]
public int InspId { get; set; }
[Column("DefectNumber")]
public int Number { get; set; }
[Column("SimulationName")]
public string Name{ get; set; }
[Column("SimulationAlgorithm")]
public string Algorithm{ get; set; }
public virtual Defect Defect { get; set; }
}
Fluent API (in OnModelCreating)
modelBuilder.Entity<Defect>()
.HasKey(h => new { h.InspId , h.Number });
modelBuilder.Entity<Defect>()
.HasOne<Simulation>(p => p.Simulation)
.WithOne(i => i.Defect)
.HasForeignKey<Simulation>(b => new { b.InspId , b.Number });
When the "Defect" class is populated through the dbContext all data is available; however, when I attempt to access the "Simulation" property of the "Defect" class I encounter the following error:
System.NullReferenceException: 'Object reference not set to an instance of an object.'
I have also verified there is valid data in our database where the "Defect" should have a "Simulation".
Any help? Throwing myself at the mercy of other coders....
Take a look at the Include method when loading from the database, it will be null unless you explicitly load:
https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.entityframeworkqueryableextensions.include?view=efcore-2.1
https://entityframeworkcore.com/querying-data-include-theninclude
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'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.
I am having difficulty getting EF7 to populate the objects referenced in a many to many join. I have followed the docs at https://docs.efproject.net/en/latest/modeling/relationships.html, but the object is still null. From what I can tell you don't have to do anything specific to get EF to populate them. I copied the sample code from the docs page as follows:
public class MyContext : DbContext
{
public DbSet<Post> Posts { get; set; }
public DbSet<Tag> Tags { get; set; }
public MyContext(DbContextOptions<MyContext> options)
: base(options)
{
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<PostTag>()
.HasKey(t => new { t.PostId, t.TagId });
modelBuilder.Entity<PostTag>()
.HasOne(pt => pt.Post)
.WithMany(p => p.PostTags)
.HasForeignKey(pt => pt.PostId);
modelBuilder.Entity<PostTag>()
.HasOne(pt => pt.Tag)
.WithMany(t => t.PostTags)
.HasForeignKey(pt => pt.TagId);
}
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public List<PostTag> PostTags { get; set; }
}
public class Tag
{
public string TagId { get; set; }
public string Title { get; set; }
public List<PostTag> PostTags { get; set; }
}
public class PostTag
{
public int PostId { get; set; }
public Post Post { get; set; }
public string TagId { get; set; }
public Tag Tag { get; set; }
}
I had to add a constructor to get it to run. I also added a Title field to the Tag class so it has more than just a key. Once I populated some data in the tables, I run the following code to retrieve from the database:
var results = _context.Posts.Include(s => s.PostTags).ToList();
When I examine the results in the debugger, the Tag objects are null even though the keys to obtain them are present. Notice that the Post objects are populated. It is always the second column of the two column key that is not joined:
This is the SQL generated by EF7:
SELECT [s].[PostId], [s].[Content], [s].[Title]
FROM [Posts] AS [s]
ORDER BY [s].[PostId]
SELECT [p].[PostId], [p].[TagId]
FROM [PostTag] AS [p]
WHERE EXISTS (
SELECT 1
FROM [Posts] AS [s]
WHERE [p].[PostId] = [s].[PostId])
ORDER BY [p].[PostId]
It doesn't appear to be fetching the Tag object at all. What am I missing here?
For completeness, I have included the sample data:
Thanks to #SOfanatic for pointing me in the right direction. I am not sure why EF doesn't automatically load the second reference class, but it doesn't. The following code will retrieve the Tag object (as well as the Post object even though we don't explicitly load it).
var results = _context.Posts.Include(s => s.PostTags).ThenInclude(t => t.Tag).ToList();
You are doing a many-to-many with what is known as Payload class. The PostTag class is technically not needed for EF to create a many-to-many relationship.
You are going to have to do something like this:
var results = _context.Posts.Include(s => s.PostTags.Select(pt => pt.Tag).ToList();
Right now your linq is loading the related entities, which are just the id's so it's of no use.
If your PostTags class is not going to have any other fields/properties you should look into creating a many-to-many without the payload
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);