Assuming I've the following Entity Framework Code-First models:
public class Employee {
[Key]
public int Id { get; set; }
public int DepartmentId { get; set; }
[ForeignKey(nameof(DepartmentId ))]
public Department Department { get; set; }
public DateTime EntryDate { get; set; }
}
public class Manager {
[Key]
public int Id { get; set; }
public int DepartmentId { get; set; }
[ForeignKey(nameof(DepartmentId ))]
public Department Department { get; set; }
}
public class Department {
[Key]
public int Id { get; set; }
[InverseProperty(nameof(Employee.Department))]
public virtual ICollection<Employee> Employees { get; set; }
[InverseProperty(nameof(Manager.Department))]
public virtual ICollection<Manager> Managers { get; set; }
}
And the following DTO object:
public class MyDto {
public int ManagerId { get; set; }
public Employee NewestEmployee { get; set; }
}
I want to use AutoMapper to convert a list of managers to a list of DTO objects. AutoMapper configuration is like this:
CreateMap<Manager, MyDto>()
.ForMember(
m => m.NewestEmployee,
opt => opt.MapFrom(
manager =>
manager.Department.Employees.OrderBy(employee => employee.EntryDate).FirstOrDefault()))
And called like this:
IEnumerable<Manager> managers = GetAllManagers();
var data = Mapper.Map<IEnumerable<MyDto>>(managers);
While this works it makes individual SQL statement requests for each manager to the employee table. Is there a way to improve performance by having only one SQL query executed (either by changing something in the Entity Framework models or AutoMapper configuration)?
Related
I have a many-to-many relationship set up with Entity Framework like this:
public class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
public ICollection<StudentCourse> StudentCourses { get; set; }
}
public class Course
{
public int CourseId { get; set; }
public string Name { get; set; }
public ICollection<StudentCourse> StudentCourses { get; set; }
}
public class StudentCourse
{
public int StudentId { get; set; }
public Student Student { get; set; }
public int CourseId { get; set; }
public Course Course { get; set; }
}
This works great, I have Students and I have Courses, and StudentCourses is the many-to-many relationship between them.
I also have an Advisor class, which has a collection of StudentCourses that the Advisor is in charge of:
public class Advisor
{
public int AdvisorId { get; set; }
public ICollection<StudentCourse> StudentCourses { get; set; }
}
I would like to get a collection of Advisors and the StudentCourses they're in charge of, but also the data properties from the Student and Course objects (like Name), all at once. This works for me:
var advisors = await _dbContext.Advisors
.Include(a => a.StudentCourses)
.ThenInclude(sc => sc.Student)
Include(a => a.StudentCourses)
.ThenInclude(sc => sc.Course)
.ToListAsync();
But is this the only way I can do that? Seems wrong to have that duplicate Include statement
I am working with the following technologies: C#, SQL Server, ASP.NET and Entity Framework and Linq.
I have a many-to-many relation in my database:
The model classes:
public class Courses
{
[Required]
public int Id { get; set; }
//more properties here
public student stud { get; set; }
}
public class inscribe
{
[Key]
public intId { get; set; }
//properties here
public student student{ get; set; }
[Required]
[ForeignKey("student")]
public string StudentId{ get; set; }
public Courses Courses{ get; set; }
}
Given a student Id, I would like to return a list of courses where he/she is inscribed.
This is what I have tried so far:
public IEnumerable<CursoDto> GetCursosAlumno(Int studentId)
{
//some code here to validate
var x = _dbContext
.Inscribe.Include(c => c.Courses)
.Where(c => c.StudentId == studentId).toList();
// x variable is a list<inscribe>
}
My problem is that I do not know how to access to the courses entity and return it as a list, for instance:
var result = X.Courses;
return result; //result is a list<courses>
How can I do it? If possible, not using a foreach block please.
Thanks
In Code First approach you don't need to add "link table" (inscribe in OP) into your models (it will be created transparently).
//Models
public class Course
{
[Key]
public int Id { get; set; }
//more properties here
public virtual /*important*/ ICollection<Student> studs { get; set; }
}
public class Student
{
[Key]
public int Id { get; set; }
//more properties here
public virtual /*important*/ ICollection<Course> courses { get; set; }
}
//Controller
var stud = _dbContext.studs.Where(s => s.Id == /*param*/id).FirstOrDefault();
var courses = stud.courses.ToList();//Real courses with id, name, etc. No Include required
Update
If you do need the "link table" (for example to add some properties like sortOrder or enrollmentDate) then the models will be a little different.
//Models
public class Course
{
[Key]
public int Id { get; set; }
//more properties here
public virtual /*important*/ ICollection<StudentCourse> studs { get; set; }
}
public class Student
{
[Key]
public int Id { get; set; }
//more properties here
public virtual /*important*/ ICollection<StudentCourse> courses { get; set; }
}
[Table("inscribe")]
public class StudentCourse
{
[Key, Column(Order = 0)]
public int StudentId {get; set'}
[Key, Column(Order = 1)]
public int CourseId {get; set'}
//extra properties
[ForeignKey("StudentId")]
public virtual Student stud { get; set; }
[ForeignKey("CourseId")]
public virtual Course course { get; set; }
}
//Controller
var courses = _dbContext.courses.Where(c/*c is "link"*/ => c.Student/*StudentCourse prop*/.Any(s/*link again*/ => s.StudentId == someId/*param*/));//again courses
As you see Include is not required.
var result = _dbContext
.Inscribe.Include(c => c.Courses)
.Where(c => c.StudentId == studentId)
.SelectMany(c => c.Courses).ToList();
This is asked many times, I know where the exact issue is but I am trying to avoid it.
Simplified POCO:
public class TaskEntity
{
public int TaskId { get; set; }
public int? AssignedToId { get; set; }
public virtual UserEntity AssignedTo { get; set; }
public int CreatedById { get; set; }
public virtual UserEntity CreatedBy { get; set; }
public int? ClosedById { get; set; }
public virtual UserEntity ClosedBy { get; set; }
}
public class UserEntity
{
public List<TaskEntity> TaskId { get; set; }
public int UserId { get; set; }
public string Name { get; set; }
}
Mappings:
public class TaskMap : EntityTypeConfiguration<TaskEntity>
{
public TaskMap()
{
ToTable("tTasks");
HasKey(x => x.TaskId);
HasRequired(x => x.CreatedBy).WithMany(x => x.TaskId).HasForeignKey(x => x.CreatedById).WillCascadeOnDelete(false);
HasOptional(x => x.ClosedBy).WithMany(x => x.TaskId).HasForeignKey(x => x.ClosedById).WillCascadeOnDelete(false);
HasOptional(x => x.AssignedTo).WithMany(x => x.TaskId).HasForeignKey(x => x.AssignedToId).WillCascadeOnDelete(false);
}
}
I have read that I should separate UserEntity in 3 different classes and make them inherit from TaskEntity, but this doesn't sounds right as It will be exactly the same user object for all these cases.
I am expecting to have table structure as follows:
tTasks
TaskId | [FK]AssignedToId | [FK]CreatedById | [FK]ClosedById
tUsers
UserId | Name
Could someone point what am I doing wrong here. Do I need to adjust my mapping somehow in order to get my table created as I expect
The answer is yes. You should adjust your mapping.
What you're doing wrong is in this line:
public List<TaskEntity> TaskId { get; set; }.
In EF you cannot get in the same navigation property all Tasks related to the UserEntity with different foreign keys. That means you need a navigation property in UserEntity to be mapped against every navigation property in TaskEntity. And as you have 3 navigation properties in every class you will need to specify which is against which.
You'll get this:
public class TaskEntity
{
public int TaskId { get; set; }
public int? AssignedToId { get; set; }
[InverseProperty("AssignedTasks")]
public virtual UserEntity AssignedTo { get; set; }
public int CreatedById { get; set; }
[InverseProperty("CreatedTasks")]
public virtual UserEntity CreatedBy { get; set; }
public int? ClosedById { get; set; }
[InverseProperty("ClosedTasks")]
public virtual UserEntity ClosedBy { get; set; }
}
public class UserEntity
{
public int UserId { get; set; }
public string Name { get; set; }
[InverseProperty("AssignedTo")]
public virtual ICollection<TaskEntity> AssignedTasks {get; set; }
[InverseProperty("CreatedBy")]
public virtual ICollection<TaskEntity> CreatedTasks {get; set; }
[InverseProperty("ClosedBy")]
public virtual ICollection<TaskEntity> ClosedTasks {get; set; }
}
With this all the mapping is done with the annotations and you can remove the TaskMap class.
You can add a List<TaskEntity> Tasks to your UserEntity that aggregates the results from the 3 previous navigation properties, but the aggregation will be done after the data is loaded and you cannot use it in Linq queries.
I'm trying to setup some navigation properties with some Entity Framework Code First models. I'd like them to look like this example:
public class Course
{
[Key]
public int CourseId { get; set; }
public string CourseName { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
public class Student
{
[Key]
public int StudentId { get; set; }
public string StudentName { get; set; }
public virtual ICollection<Course> Courses { get; set; }
}
public class StudentCourses
{
[Key, Column(Order = 0)]
public int StudentId { get; set; }
public virtual Student Student { get; set; }
[Key, Column(Order = 1)]
public int CourseId { get; set; }
public virtual Course Course { get; set; }
}
So Student and Course relationships would be established in the StudentCourses table. An instance of the student class would automatically reference all of that students courses, and vice versa an instance of the Course class would automatically reference all of its Students. And an instance of the StudentCourses class would automatically reference its Student and Course. But when I try to Update-Database, the relationships don't seem to get properly interpreted. Is there anything I'm missing here? Perhaps some configuring needs to be done in the context class? Most of the examples of navigation properties just show one-to-many relationship navigation properties.
You need to construct your models as shown below when you have a M : M relationship. You don't need to construct junction table. EF will create one for you when you do the data migration.
Model configuration using Conventions.
public class Student
{
public Student()
{
this.Courses = new HashSet<Course>();
}
public int StudentId { get; set; }
public string StudentName { get; set; }
public virtual ICollection<Course> Courses { get; set; }
}
public class Course
{
public Course()
{
this.Students = new HashSet<Student>();
}
public int CourseId { get; set; }
public string CourseName { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
Your context class should be like this.
public class YourDBContext : DBContext
{
public YourDBContext () : base("Default")
{
}
public DbSet<Student> Students { get; set; }
public DbSet<Course> Courses { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
}
}
After following Sampath's advice, I actually decided I wanted to attach some other properties to the relationship. So I ended up defining the StudentCourses class afterall like this:
public class StudentCourses
{
[Key, Column(Order = 0)]
public int StudentId { get; set; }
public virtual Student Student { get; set; }
[Key, Column(Order = 1)]
public int CourseId { get; set; }
public virtual Course Course { get; set; }
public int Grade { get; set; }
}
So I changed Student and Course like this:
public class Course
{
[Key]
public int CourseId { get; set; }
public string CourseName { get; set; }
public virtual ICollection<StudentCourses> Students { get; set; }
}
public class Student
{
[Key]
public int StudentId { get; set; }
public string StudentName { get; set; }
public virtual ICollection<StudentCourses> Courses { get; set; }
}
And most importantly, I did not add StudentCourses to the DbContext. So after Update-Database was performed, EF automatically created the table for StudentCourses, and the navigation properties all work.
This will create two tables "Ingredient" and "Recipe" and an additional table for many-to-many mapping.
public class DC : DbContext {
public DbSet<Ingredient> Ingredients { get; set; }
public DbSet<Recipe> Recipes { get; set; }
}
public class Ingredient {
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Recipe> Recipes { get; set; }
}
public class Recipe {
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Ingredient> Ingredients { get; set; }
}
Question: I want to include additional column "quantity" in the third mapping table that will be created by Entity Framework. How to make that possible? Thanks in advance.
When you've got some extra information, I suspect it won't really count as a mapping table any more - it's not just a many-to-many mapping. I think you should just model it as another table:
public class Ingredient {
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<RecipePart> RecipeParts { get; set; }
}
public class RecipePart {
public int Id { get; set; }
public Ingredient { get; set; }
public Recipe { get; set; }
// You'll want to think what unit this is meant to be in... another field?
public decimal Quantity { get; set; }
}
public class Recipe {
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<RecipePart> Parts { get; set; }
}
So now you don't really have a many-to-many mapping - you have two ordinary many-to-one mappings. Do you definitely need to "ingredient to recipes" mapping exposed in your model at all? If you want to find out all the recipes which use a particular ingredient, you could always do a query such as:
var recipies = DB.Recipies.Where(r => r.Parts
.Any(p => p.Ingredient == ingredient));