I have a model that looks like this
public abstract class Item
{
public int ItemId { get; set; }
public String Title { get; set; }
public String Description { get; set; }
public DateTime PurchaseDate { get; set; }
public ICollection<String> Pictures { get; set; }
public Int32 MinimumPrice { get; set; }
public DateTime Deadline { get; set; }
public Boolean VisibleBids { get; set; }
public Boolean Handled { get; set; }
public DateTime PlacementDate { get; set; }
public ApplicationUser User { get; set; }
}
In my controller I do
db.Items.ToList()
This leaves the Pictures field for all fetched objects null because its how the entity framework works. What is a good solution to fetch them in one query?
I hope you already done with Navigation properties between your tables, Now you just need to make your collection virtual and use the concept of eager loading when you need data from both the tables
public virtual ICollection<String> Pictures { get; set; }
and use include in linq like
db.Items.Include("Pictures").ToList()
So here by making virtual navigation you are saying that only take the data of related entity when you needed and whenever you need the data use the Include for eager loading.
For setting navigation properties please have a look on the code.
Suppose the scenario where we have a Post and on this we have multiple comments like
class Posts
{
public int PostsId { get; set; }
public string PostsDescription { get; set; }
public virtual ICollection<Comments> Comments { get; set; }
}
class Comments
{
public int CommentsId { get; set; }
public string CommentsDescription { get; set; }
public int PostsId { get; set; }
public virtual Posts Posts { get; set; }
}
Related
This is done using MVC .net framework and entity framework "database first" approach. There is a many to many relationship between two tables. They are connected through third table that has combined key as id from first table and id from second table.
public class ManyToManyTable
{
[Required]
[Key, Column(Order=0)]
public int firsttableid { get; set; }
[Required]
[Key, Column(Order=1)]
public int secondtableid { get; set; }
public int something { get; set; }
[ForeignKey("firsttableid")]
public virtual FirstTable firstTable { get; set; }
[ForeignKey("secondtableid")]
public virtual SecondTable secondTable { get; set; }
}
First and Second table have some id which is primary key.
I want to create View and Controller method that enables master detail entry form for this ManyToManyTable. that would have FirstTable in Master and SecondTAble in details, and all to be saved in ManyToManyTable when button Save is pressed.
Of course, both First and Second Table have this property:
public virtual ICollection<ManyToManyTable> ManyToManyTables { get; set; }
What is the easiest way to implement cases like this one?
Thank you!
EF has a default conventions for many-to-many relationships. No need to create specific
mapping class. You have to include navigation properties in both "FirstTable" and "SecondTable" Class as shown below.
public class FirstTable
{
public FirstTable()
{
secondTableProperties = new HashSet<SecondTable>();
}
public int Id { get; set; }
public int MyProperty2 { get; set; }
public int MyProperty3 { get; set; }
public virtual ICollection<SecondTable> secondTableProperties { get; set; }
}
public class SecondTable
{
public SecondTable()
{
FirstTableProperties = new HashSet<FirstTable>();
}
public int Id { get; set; }
public int MyProperty2 { get; set; }
public int MyProperty3 { get; set; }
public virtual ICollection<FirstTable> FirstTableProperties { get; set; }
}
Remove mapping class from DBContext , only include above two classes. Build and run the application , EF will automatically create a Mapping table in SQL server. Usually the Mapping table contains only the primary keys of other two tables.
You can use Fluent API to take some control on the created mapping table
modelBuilder.Entity<FirstTable>()
.HasMany<SecondTable>(s => s.FirstTableProperties)
.WithMany(c => c.secondTableProperties)
.Map(cs =>
{
cs.MapLeftKey("FirstTableId");
cs.MapRightKey("SecondTableId");
cs.ToTable("ManyToManyTable");
});
If you want to work with a join table with additional properties, above mentioned many-to-many relationship won't work . In that case you will have to create two one-to-many relationships as shown below.
public class FirstTable
{
public int Id { get; set; }
public int MyProperty2 { get; set; }
public virtual ICollection<ManyToManyTable> manytomany { get; set; }
}
public class SecondTable
{
public int Id { get; set; }
public int MyProperty2 { get; set; }
public virtual ICollection<ManyToManyTable> manytomany { get; set; }
}
public ManyToManyTable
{
[Required]
[Key, Column(Order=0)]
public int firsttableid { get; set; }
[Required]
[Key, Column(Order=1)]
public int secondtableid { get; set; }
public int AdditionalProperty { get; set; }
public virtual FirstTable first { get; set; }
public virtual SecondTable Second { get; set; }
}
I created models and performed code first migration which resulted in prepopulated up down methods.
However at a later stage I added new models to my application. The new models I added were Cart, OrderDetails and Order. I then typed add-migration for each of these models which as a result produced empty up down methods.
I would like to ask why are these up down methods empty when I added a new model.
I referenced these models in the dbcontext, the same dbcontext that referenced previously created models.
These are the new model classes that I added:
public class OrderDetail
{
public int OrderDetailId { get; set; }
public int OrderId { get; set; }
public int BookId { get; set; }
public int Quantity { get; set; }
public decimal UnitPrice { get; set; }
public virtual Book Books { get; set; }
public virtual Order Order { get; set; }
}
public class Cart
{
[Key]
public int RecordId { get; set; }
public string CartId { get; set; }
public int BookId{ get; set; }
public int Count { get; set; }
public virtual Book Book { get; set; }
}
class Order
{
public int OrderId { get; set; }
public string Username { get; set; }
public string FirstName { get; set; }
}
Here is my dbcontext
public BookStoreOnlineDB() : base("name=BookStoreOnlineDB")
{
}
public System.Data.Entity.DbSet<BookStoreOnline.Models.Book> Books { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.Author> Authors { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.BookStatus> BookStatus { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.Genre> Genres { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.Order> Orders { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.OrderDetail> OrderDetails { get; set; }
public System.Data.Entity.DbSet<BookStoreOnline.Models.Cart>Carts { get; set; }
}
In summary, how do I populate the new up down methods with regards to the newly added Cart, OrderDetail and Detail models.
N.B. The orderDetails model and cart model reference the book model(book model contains had data migration performed on it at an earlier stage and contains populated up down methods).
New to this and would really appreciate help.
Thanks
Answer:
in PM Console:
add-migration initialcreate
//this included the newly added models e.g their ids,(cart,orderdetails, order models) to the up down methods
I'm an ASP.NET MVC4 beginner and I'm trying to create a blog kind of. I have a problem with creating relationships in my models. Background of my issue is that, I have a model (Users.cs) with user information, a model (Posts.cs) containing posts information, and a third model (Comments.cs) containing comments information.
So a user can have many posts but a post can belong to only one user,
a user can have many comments but a comment can belong to only a user,
a post can have many comments but a comment can only belong to a post,
My question is, how do I write the three models? So far I have this:
public class Users
{
public int UserID { get; set; }
public string Firstname { get; set; }
public string Lastname { get; set; }
public DateTime DOB { get; set; }
public string Sex { get; set; }
public string Email { get; set; }
public DateTime RegDate { get; set; }
public string Username { get; set; }
public string Password { get; set; }
public string PasswordSalt { get; set; }
public virtual List<Posts> Post { get; set; }
public virtual List<Comments> Comment { get; set; }
}
class Posts
{
public int PostID { get; set; }
public string PostTitle { get; set; }
public string PostContent { get; set; }
public DateTime PostDate { get; set; }
public int AuthorID { get; set; }
public int CommentID { get; set; }
public virtual List<Comments> Comment { get; set; }
public virtual Users user { get; set; }
}
public class Comments
{
public int CommentID { get; set; }
public string Comment { get; set; }
public DateTime CommentDate { get; set; }
public int AuthorID { get; set; }
public int PostID { get; set; }
public virtual Posts post { get; set; }
public virtual Users user { get; set; }
}
Please how do I write the three models correctly? Help!!!
You have strongly typed model classes, and you're already using them correctly. You just need to remove the redundant properties pointing to ID's - Comments doesn't need an int AuthorID pointing to the author when it already has Users user.
Remove these properties:
class Posts
{
public int AuthorID { get; set; }
public int CommentID { get; set; }
}
public class Comments
{
public int AuthorID { get; set; }
public int PostID { get; set; }
}
I am still on my quest to port from a Model First to Code First implementation of EntityFramework. I have made significant progress, with the help of Eranga. I have run into another snag, and I just cant explain what is hapening. I have two Entity objects Topic and Course
A Topic can have one Course that is required
A Course can have 0 or more topics
when i execute the following linq it generates wierd SQL
var topics = from o in db.Topics where o.ParentTopic == null &&
o.Course.Id == c.Id select o;
The SQL generated is
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Name] AS [Name],
[Extent1].[ShortDescription] AS [ShortDescription],
[Extent1].[LongDescription] AS [LongDescription],
[Extent1].[Property] AS [Property],
[Extent1].[Difficulty] AS [Difficulty],
[Extent1].[Weight] AS [Weight],
[Extent1].[Course_Id] AS [Course_Id],
[Extent1].[ParentTopic_Id] AS [ParentTopic_Id],
[Extent1].[Course_Id1] AS [Course_Id1]
FROM [dbo].[Topics] AS [Extent1]
WHERE ([Extent1].[ParentTopic_Id] IS NULL) AND ([Extent1].[Course_Id] = #p__linq__0)
Notice that there is an added field called Course_Id1 that is not in my object and not declared as a foreign key. I thought that in OnModelCreating() I had specified the parent child relationship correctly from both sides (I would have thought you only needed to do it from either side), but i cant get EntityFramework not to generate the extra field that obviously does not exist in the database. Remember my database was originally created using a ModelFirst approach.
Can anyone explain where the extra field is comming from????
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
//Topic
modelBuilder.Entity<Topic>()
.HasRequired(m => m.Course)
.WithMany(m=>m.Topics)
.HasForeignKey(m => m.Course_Id);
modelBuilder.Entity<Topic>()
.HasOptional(m => m.ParentTopic)
.WithMany(m => m.ChildTopics)
.HasForeignKey(m => m.ParentTopic_Id);
//////// lots of code removed for brevity. //////
modelBuilder.Entity<Course>()
.HasMany(m=>m.Topics)
.WithRequired(m => m.Course)
.HasForeignKey(m => m.Course_Id);
}
public partial class Topic
{
public int Id { get; set; }
[Required]
public string Name { get; set; }
public string ShortDescription { get; set; }
public string LongDescription { get; set; }
public string Property { get; set; }
public double? Difficulty { get; set; }
public double? Weight { get; set; }
[JsonIgnore]
public virtual Course Course { get; set; }
public int Course_Id { get; set; }
[JsonIgnore]
public virtual ICollection<Question> Questions { get; set; }
[JsonIgnore]
public virtual ICollection<Topic> ChildTopics { get; set; }
[JsonIgnore]
public virtual Topic ParentTopic { get; set; }
public int? ParentTopic_Id { get; set; }
[JsonIgnore]
public virtual ICollection<RTIQueueEntryData> RTIQueueEntryData { get; set; }
[JsonIgnore]
public virtual ICollection<Intervention> Interventions { get; set; }
[JsonIgnore]
public virtual ICollection<RtiStudentGroup> RtiStudentGroups { get; set; }
}
public partial class Course
{
public int Id { get; set; }
[Required]
public string Name { get; set; }
[Required]
public string Description { get; set; }
public string Version { get; set; }
public string Year { get; set; }
public string ImportedId { get; set; }
[Required]
public string LocalCourseNumber { get; set; }
[Required]
public string NCESCourseNumber { get; set; }
[Required]
public string StateCourseNumber { get; set; }
public int? Grade { get; set; }
[JsonIgnore]
public virtual ICollection<Topic> PerformanceIndicators { get; set; }
[JsonIgnore]
public virtual Department Department { get; set; }
public int DepartmentId { get; set; }
[JsonIgnore]
public virtual ICollection<StudentGroup> StudentGroups { get; set; }
[JsonIgnore]
public virtual ICollection<CutPointTemplate> CutPointTemplates { get; set; }
[JsonIgnore]
public virtual School School { get; set; }
public int School_Id { get; set; }
[JsonIgnore]
public virtual ICollection<Staff> RTIStaff { get; set; }
[JsonIgnore]
public virtual ICollection<Topic> Topics { get; set; }
}
You have another relationship between Course and Topic created by convention due to this navigation property:
public virtual ICollection<Topic> PerformanceIndicators { get; set; }
EF will put an (invisible, not exposed) end of the relationship into the Topic class. By default the relationship is one-to-many. Hence you get an additional foreign key property in the Topics table (= Course_Id1).
Today I've been working with MVC for the first time. Also normally I use the EF with model first, but I wanted to try POCO.
So I've made my 3 entities and when I try to make a controller I get an error:
Unable to retrieve metadata for "BookExchange.Models.Exchange". Unable to determine the principal end of an association between the types "BookExchange.Models.Exchange" and "BookExchange.Models.Book". The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations.
My 3 classes:
public class Book
{
public int BookID { get; set; }
public string Name { get; set; }
public string Author { get; set; }
public string ISBN10 { get; set; }
public int PersonID { get; set; }
public virtual Person Person { get; set; }
public virtual Exchange Exchange { get; set; }
}
public class Person
{
public int PersonID { get; set; }
public string Name { get; set; }
public virtual ICollection<Book> Books { get; set; }
public virtual ICollection<Exchange> Exchanges { get; set; }
}
public class Exchange
{
[Key]
public int BookID { get; set; }
public int PersonID { get; set; }
public DateTime ReturnDate { get; set; }
public virtual Person Person { get; set; }
public virtual Book Book { get; set; }
}
Does anyone know what I'm doing wrong? I don't want to lose the association properties.
Thanks in advance!
Try adding foreign key properties for your references. E.g.
public class Book
{
public int BookID { get; set; }
public string Name { get; set; }
public string Author { get; set; }
public string ISBN10 { get; set; }
public virtual Person Person { get; set; }
public int PersonID { get; set; }
public virtual Exchange Exchange { get; set; }
public int ExchangeID { get; set; }
}
public class Person
{
public int PersonID { get; set; }
public string Name { get; set; }
public virtual ICollection<Book> Books { get; set; }
public virtual ICollection<Exchange> Exchanges { get; set; }
}
public class Exchange
{
public int ExchangeID { get; set; }
public int BookID { get; set; }
public virtual Book Book { get; set; }
public int PersonID { get; set; }
public virtual Person Person { get; set; }
public DateTime ReturnDate { get; set; }
}
Also, take a look at ScottGu's post on code first and this EF post on conventions.
Try this: (Remove database, so EF will create new)
public class Book
{
public int Id { get; set; }
public string Name { get; set; }
public string Author { get; set; }
public string ISBN { get; set; }
public virtual Person Person { get; set; }
public virtual Exchange Exchange { get; set; }
}
public class Person
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Book> Books { get; set; }
public virtual ICollection<Exchange> Exchanges { get; set; }
}
public class Exchange
{
public int Id { get; set; }
public DateTime ReturnDate { get; set; }
public virtual Person Person { get; set; }
public virtual Book Book { get; set; }
}
It's your one on one associations.
Remove one reference between exchange or book, so Code-first can decide which one is more important in your one on one relation (Book <--> Exchange)
If you want to know why, you should read this: