I'm struggling with creating a simple one-to-many relationship using Code First in EF. I want it to generate daatabase for me but couldn't figure out how to write these classes so it would create it.
I have these classes:
public class Book
{
public int ID { get; set; }
public string Author { get; set; }
public ICollection<Page> Pages { get; set; }
}
public class Page
{ [Key]
public int BookID { get; set; }
public Book Book { get; set; }
public string OtherField { get; set; }
}
But I get error while it ties to generate database:
Unable to determine the principal end of an association between the types 'MvcApplication1.Models.Page' and 'MvcApplication1.Models.Book'. The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations
I just want to generate two simple tables, "Book" with ID as primary key, and Page with BookID as a primary and foreign key. It really should be simple but I just can't figure it out.
But that is not one-to-many relationship. That is one-to-one relation ship which says that each book has exactly one page. The error says that it cannot determine if the book or the page is principal in the one-to-one relation.
You must modify your entities like this:
public class Book
{
public int ID { get; set; }
public string Author { get; set; }
public virtual ICollection<Page> Pages { get; set; }
}
public class Page
{
public int ID { get; set; }
public int BookID { get; set; }
public virtual Book Book { get; set; }
public string OtherField { get; set; }
}
Related
i am trying to define a database model in code-first to see and display which user is assigned as a specialist for the record data.
I have a very simple model for the user:
public class User
{
public int ID { get; set; }
public string userName { get; set; }
public string firstName { get; set; }
public string lastName { get; set; }
....
}
Next I have defined two (simple) models which define the data that can be edited by the user and the specialist should be assigned to using a dropdownlist:
public class Order
{
public int ID { get; set; }
public string orderNumber { get; set; }
public int specialistID { get; set; }
public virtual User specialist{ get; set; }
}
public class Part
{
public int ID { get; set; }
public string partNumber { get; set; }
public string description { get; set; }
public int specialistID { get; set; }
public virtual User specialist{ get; set; }
}
What kind of relation between the models can be used without having a navigation property for each table in the User model?
Do I need to use additional tables to define the relationship: User.Id-Order.specialistID and the relationship: User.Id-Part.specialistID ?
Is there a smarter way out-of-the-box by Entity Framework?
Many thanks for your answers.
Pascal
By default when you add forign-key constraint to the many-to-one table the Entity Framework add virtual property to the entity class and virtual ICollection to the User.
I am buys designing the model below:
public class LogModel
{
public class UserActivityLogs
{
[Key]
public int id { get; set; }
//Id of the user
public string userId { get; set; }
//Time of the log
public DateTime time { get; set; }
public LogActions action { get; set; }
}
// Types of actions to log
public class LogActions
{
[Key]
public int id { get; set; }
public string name { get; set; }
public string description { get; set; }
}
}
Now what I would like to know is do I need to add a table in the context for Logactions as well as UserActivityLogs or will EF see that the two tables are linked and create the log action table automatically?
Also have I specified my relationships correctly? What I was aiming for is that I can define multiple types of Logactions and then a userlog will then have a single log action associated to it.
First, don't use nested classes, it's a needless complication. Use namespaces to organize classes.
Second, don't use plural names for classes. One instance of class represents one entity. Also, use CamelCase names for properties.
Third, yes, Entity Framework will be aware of the associations between the two classes and create a database model with two tables and a foreign key.
So this leaves you with:
namespace MyApp.LogModel
{
public class UserActivityLog
{
[Key]
public int Id { get; set; }
public string UserId { get; set; }
public DateTime Time { get; set; }
public LogAction LogAction { get; set; }
}
public class LogAction
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
}
I have a relationship set up between 2 tables using code first and Fluent API. This works and the schema is generated with the correct fields and key assignments. However, my problem is I need to be able to say SupplyPoint.SupplyPointPricing in my resultant Model. What I have below only gives me the other way around.
I figure there must be a way to keep the structure I have but just MAP SupplyPoint.
public partial class SupplyPoint
{
[Key]
public int SupplyPointId { get; set; }
public string SupplyPointName { get; set; }
}
public class SupplyPointPricing
{
public int SupplyPointPricingId { get; set; }
public int? SupplyPointId { get; set; }
[ForeignKey("SupplyPointId")]
public virtual SupplyPoint SupplyPoint { get; set; }
}
Then I use Fluent API and this gives me the 1-1 between the tables and the Schema I expect
modelBuilder.Entity<SupplyPointPricing>()
.HasOptional(a => a.SupplyPoint)
.WithMany()
.HasForeignKey(u => u.SupplyPointId);
Last time I had this problem I had to change the design around and have a foreign key in the SupplyPoint table. On that previous occasion that was OK since it was a 1-1 required where there are always a matching record. This time around I need to keep this structure since there is 1-0 between SupplyPoint and SupplyPointPricing.
This is how I have always done 1-to-1 relationships with my models, without using Fluent mapping:
public partial class SupplyPoint
{
[Key]
public int SupplyPointId { get; set; }
public virtual SupplyPointPricing SupplyPointPricing { get; set; }
}
public class SupplyPointPricing
{
[Key, ForeignKey("SupplyPoint")]
public int SupplyPointId { get; set; }
public virtual SupplyPoint SupplyPoint { get; set; }
}
As you can see, the SupplyPointPricing does not have an Id of its own, but only the Id of the SupplyPoint, which acts as a key in the 1-to-1 relatioship.
The only thing I'm not sure of is if the SupplyPointId can be a nullable int.
This will not create a foreign key on the SupplyPoint, so if you don't have a Pricing, the SupplyPoint.SupplyPointPricing property will be null.
I'm very new to ASP.NET and could use some help.
For this scenario, I have 2 classes. One is a "project" class and the other is a "company" class. Essentially, what I need is one single "company directory" of all the companies we have relationships with, but I need to be able to freely slot them into 3 different slots within a project. It is possible that the same company could occupy all 3 slots, but it's equally likely that a different company will be placed in each slot.
Here are my classes:
public class Project
{
public int ID { get; set; }
public string Name { get; set; }
public int ClientID { get; set; }
public int PublisherID { get; set; }
public int DeveloperID { get; set; }
public Company Client { get; set; }
public Company Publisher { get; set; }
public Company Developer { get; set; }
}
public class Company
{
public int ID { get; set; }
public string Name { get; set; }
}
When I have used this basic outline in the past, the complex types I specify in the bottom half of the model definition will be auto generated based on the matching int ID properties specified earlier. For example, If I had a complex type "User" that was drawing it's data from a user table in my database, specifying (int UserID) within my class followed by (User User), the UserID field would be the actual field in my project table and the User object I specify will automatically be an object containing all the User information from the user table.
Using this method as I did in the classes specified above, however, does not work in the way I expected and instead creates not only ClientID, PublisherID, and DeveloperID but also creates CompanyID, CompanyID1, and CompanyID2 which are the fields that will actually be used when attempting to instantiate the Company objects I specified (even though those fields will contain null always).
Is there any way around this?
You just need to specify that your int properties are the foreign keys to your navigation properties.
public class Project
{
public int ID { get; set; }
public string Name { get; set; }
public int ClientID { get; set; }
public int PublisherID { get; set; }
public int DeveloperID { get; set; }
[ForeignKey("ClientID")]
public Company Client { get; set; }
[ForeignKey("PublisherID")]
public Company Publisher { get; set; }
[ForeignKey("DeveloperID")]
public Company Developer { get; set; }
}
I feel like this should have a simple answer, but I can't find it.
I have 2 POCOs:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Product
{
public int Id { get; set; }
public int CategoryId { get; set; }
}
Notice that there are no object references on either POCO. With Code-First, how do I make EF4 CTP5 define a relationship between the two database tables?
(I know this is an unusual scenario, but I am exploring what's possible and what's not with Code-First)
No, this is not possible. As you can see below, all of the fluent API methods for setting up associations require specifying the Navigation Property as their parameter.
HasMany<TTargetEntity>(Expression<Func<TEntityType, ICollection<TTargetEntity>>> navigationPropertyExpression)
HasOptional<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
HasRequired<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
Is there any particular reason you don't want to use object references? It looks very elegant to use them:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int Id { get; set; }
public Category Category { get; set; }
}
And you can still access the Category Id via your product as product.Category.Id.