I'm continuing my venture with Entity Framework, but now I'm stuck again. I've two small classes:
public class Machine
{
public int MachineID { get; set; }
public string Name { get; set; }
[Required]
[ForeignKey("InstalledByID")]
public virtual Employee InstalledBy { get; set; }
public int InstalledByID { get; set; }
[Required]
[ForeignKey("LastServicedID")]
public virtual Employee LastServiced { get; set; }
public int LastServicedID { get; set; }
}
public class Employee
{
public int EmployeeID { get; set; }
public string Name { get; set; }
}
I'm trying to set two properties: InstalledBy and LastServiced. Both of these properties are instances of an Employee class. Additionally, I could care less that there are two REVERSE properties on the Employee class that tells a list of machines installed as well as machines repaired. When I try to Update-Database after a Migration, I get an error. I thought the ForeignKeyAttribute was the key, but apparently it's not working for me. Here is the error:
Introducing FOREIGN KEY constraint 'FK_dbo.Machines_dbo.Employees_InstalledByID' on table 'Machines' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
Could not create constraint. See previous errors.
Also, I've tried dabbling in the OnModelCreating and FluentAPI, but my attempts did not work. Any pointers as to what I'm doing wrong and how to fix it would be greatly appreciated. Thank you, all.
Related
I've hit a snag while building a .net mvc site. I have 2 related objects and am struggling with properly linking them. Specifically:
public class Address
{
public int AddressId { get; set; }
public string Street { get; set; }
public string City { get; set; }
public string State { get; set; }
public string PostCode { get; set; }
[ForeignKey("AddressCategory")] // <-- EF adds field to below object's table
public int AddressCategoryId { get; set; }
public virtual AddressCategory AddressCategory { get; set; }
}
public class AddressCategory
{
public int AddressCategoryId { get; set; }
public string Description { get; set; }
}
Adding the [ForeignKey] data annotation to the Address object results in EF adding an Address_AddressId column to the AddressCategory table, which I don't want (or need) to happen.
I've tried to omit the ForeignKey attribute, but then I run into other errors because .net can't link the tables (e.g. Unknown column 'Extent1.AddressId' in 'field list'). Additionally, I wouldn't be able to use:
var addresses = db.Addresses.Include(l => l.AddressCategory);
Is there any way to link the 2 tables without EF adding an additional column to the AddressCategory table?
Thank you to #cloudikka for responding. After much trial-and-error I seem to have gotten it to work simply by omitting any ForeignKey reference from either object. I let EF rebuild the database and perform all scaffolding (CRUD forms) and they have been created perfectly.
My take-away is that foreign key attributes should be used for parent-child relationships, but not for look-up tables. I clearly have much to learn about asp.net mvc!
I probably found a bug... at least it's annoying to me so I would appreciate if someone confirms this:
public int PriorityConfigurationSettingId { get; set; }
[ForeignKey("PriorityConfigurationSettingId")]
public virtual PriorityConfigurationSetting
PriorityConfigurationSetting{get;set; }
to
public int PriorityConfigurationSettingId { get; set; }
[ForeignKey("PriorityConfigurationSettingId")]
public virtual LookUp PriorityConfigurationSetting { get; set; }
When I change the name of a foreign key entity name from PriorityConfigurationSetting to LookUp. After done the model changes i try to get the script through EF Code Fist Migration, I didn't get any changes.
This is making me feel like an idiot. Entity Framework is supposed to be fairly simple, yet I can't sort this out myself and clearly I've got a fundamental misunderstanding. I hope it doesn't turn out to be an idiot-question - sorry if it is.
Three code-first objects, related to one another.
public class Schedule
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public DateTime Start { get; set; }
public DateTime End { get; set; }
public virtual ICollection<Charge> Charges { get; set; }
}
public class Charge
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public decimal Rate { get; set; }
public Type Type { get; set; }
}
public class Type
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public string TypeName { get; set; }
}
When I query this, I want all related types, so:
Schedule currentSchedule = _Context.Schedules
.Include("Charges.Type")
.Where(cs => cs.Start < dateWindow && cs.End > dateWindow)
.First();
In C#, this has been working fine.
The problem arises because we're not stopping at C#, but passing the data onto a javascript library called Breeze with smooths out data operations at the client end. Breeze has a bug/feature which demands that EF relationships between objects be specified at BOTH ENDS. So when I do my query above, I don't end up with any Types, because their relationship with Charge isn't directly specified.
So I change it to this:
public class Type
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public string TypeName { get; set; }
public virtual Charge Charge { get; set; }
}
Because virtual is a navigation property, so that should enable Breeze should now to go both ways across the relationship without changing the data structure. But EF doesn't like this. It tells me:
Unable to determine the principal end of an association between the
types 'Core.Charge' and 'Core.Type'. The principal end of this
association must be explicitly configured using either the
relationship fluent API or data annotations
Fair enough. I can see how this could be confusing. Now, my understanding is that if you define a foreign key in a dependent class, it has to be that classes' primary key. So we change it to:
public class Type
{
[Key, ForeignKey("Charge"), DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public string TypeName { get; set; }
public virtual Charge Charge { get; set; }
}
And that seems to work but ... it's stopped loading any Type information when you ask for a schedule. Messing around with the includes doesn't seem to do anything at all.
What's going on, and what have I done wrong?
You haven't only added a navigation property (Type.Charge) to an existing model/relationship. Instead you have changed the relationship completely from a one-to-many to a one-to-one relationship because by default if a relationship has only one navigation property EF assumes a one-to-many relationship. With your change you have configured a one-to-one relationship.
Those relationships have different foreign keys: The original one-to-many relationship has a separate foreign key in the Charge table (probably named Type_RowId or similar). Your new relationship has the foreign key at the other side in table Type and it is the primary key RowId. The Charges you are loading together with the Schedule probably don't have any related Type with the same primary key, hence no Type is loaded.
If you actually want to reproduce the old (one-to-many) relationship with just a navigation property at the other side you must add a collection to Type instead of a single reference:
public class Type
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public string TypeName { get; set; }
public virtual ICollection<Charge> Charges { get; set; }
}
Are you sure that you want to put ForeignKey on RowId, I think you may want to define some relationship like this
public class Type
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public Guid RowId { get; set; }
public string TypeName { get; set; }
public int ChargeId { get; set; }
[ForeignKey("ChargeId")]
public virtual Charge Charge { get; set; }
}
I am trying to code the following in code first... since I am just begining I am not able to.. please help.. thanks in advance
1. Student: Student will have student ID, First Name, Last Name
Student should belong to one class and one section(basically one to one relationship with each entity)
2. Classes: Class will have ClassId, Name
Class should have collection of students and collection of sections(basically many to many relationship with each entity)
3. Sections: Section will have SectionID, Name
Section should belong to one class and should have collection of students(basically one to one relation with class and one to many relation with Students)
Below is the code for the same
Students.cs
public class Students
{
public int StudentsId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string UserName { get; set; }
public decimal Grade { get; set; }
public int ClassesId { get; set; }
public Classes Classes { get; set; }
public int SectionsId { get; set; }
public Sections Sections { get; set; }
}
Classes.cs
public class Classes
{
public int ClassesId { get; set; }
public string Name { get; set; }
public ICollection<Sections> Sections { get; set; }
}
Sections.cs
public class Sections
{
public int SectionsId { get; set; }
public string Name { get; set; }
public int ClassesId { get; set; }
public Classes Classes { get; set; }
public ICollection<Students> Students { get; set; }
}
If I do this I get error saying:
Introducing FOREIGN KEY constraint
'FK_dbo.Sections_dbo.Classes_ClassesId' on table 'Sections' may cause
cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON
UPDATE NO ACTION, or modify other FOREIGN KEY constraints.
I know I can get rid of this error using fluent APIs and telling not to cascade on delete, but I don't want to do that. Is there any other solution to this?? Please help
With your current model, no, there is no other way than disabling casdading delete for some of the relationships.
All your relationships are required, that means that if a class is deleted you delete the sections and the students of that class (Classes has a not exposed collection of students due to the required navigation property Classes in Students). But if the sections are deleted the students of that sections are deleted as well - and that's the second delete path to Students.
I don't know the exact meaning of your model but to me it sounds strange to delete all students of a class if the class gets deleted. Does a student always must have a class or couldn't he temporarily be without class assignment (and section assignment as well)? Maybe the student has a holiday semester for half a year and doesn't participate in any class?
In that case you could make the relationships of Students optional. Just declare the foreign key properties as nullable:
public class Students
{
//...
public int? ClassesId { get; set; }
public Classes Classes { get; set; }
public int? SectionsId { get; set; }
public Sections Sections { get; set; }
}
This would fix your problem of multiple cascading delete paths in the Students class because by default optional relationships don't have cascading delete enabled. The relationship between Classes and Sections is still required, so deleting a class will delete all sections belonging to the class as well, but it won't delete the students anymore.
I'm having an issue that i just can't seem to figure out. Lets say I have 2 Entities defined in my domain; Person and Document. Below is the definition for Document :
public class Document
{
public int Id { get; set; }
[Required]
[StringLength(255)]
public string Title { get; set; }
public DateTime Date { get; set; }
public virtual Person Owner{ get; set; }
public virtual Person AssignedTo { get; set; }
}
Now, when EF CTP4 creates the SQL table on initialize, there is only one field mapping to a Person.Id being Owner_id. Whatever i try, the field for AssignedTo is never created.
Anything that could solve this?
Regards,
avsomeren
Your code perfectly created the desired schema in the database for me:
If you don't get this schema in you DB then my guess is that something is not right with the rest of your object model. Could you post your full object model please?
Another Solution:
While your current Document class will give you the desired results, but you can still take advantage of the Conventions for Code First and explicitly specify the FKs for your navigation properties:
public class Document
{
public int Id { get; set; }
[Required][StringLength(255)]
public string Title { get; set; }
public DateTime Date { get; set; }
public int OwnerID { get; set; }
public int AssignedToID { get; set; }
public virtual Person Owner { get; set; }
public virtual Person AssignedTo { get; set; }
}
Code First will now infer that any property named <navigation property name><primary key property name> (e.g. OwnerID), with the same data type as the primary key (int), represents a foreign key for the relationship.
This essentially results to the same DB schema plus you have the FKs on your Document object as well as navigation properties which gives you ultimate flexibility to work with your model.