Motivation : My EF4.1 DbContext is saving Entities in the wrong order
Reason : Lack of navigation properties on my models
How I want to fix it :
I want to set up foreign key relationships in my DbContext. The catch is that my entity objects have no navigation properties (I'm using it to populate a web service and then firing DTO objects over to my application).
The classes below would be an example. In MinorClass, I want to configure my context so that it knows MajorClassID is a foreign key. The articles I've been finding on the internet on how to explicitly define Foreign Keys involve using navigational properties, which my objects dont have.
Is there a way to map this relationship?
public class MinorClass
{
public Guid ID {get;set:}
public Guid MajorClassID {get;set;} // foreign key
public string Name {get;set;}
}
public class MajorClass
{
public Guid ID {get;set;}
public string Name {get;set;}
}
Navigation property is primary construct whereas foreign key is helper (imho wrong helper). EF recognizes ordering of DB commands by relationships which are defined by navigation properties. You cannot define relation just by foreign key. You need navigation property on at least one side of the relation.
Related
I have two tables
People Relation
------------- -----------------
Id (int) Id (int)
Name (string) ParentPeopleId (int)
ChildPeopleId (int)
I need to get all people by Relation table with union all.
The relation table has two foreign keys. And there is one problem with mapping them. The mapping is one to many. People has many Relation, Relation has one People.
I mapped them like this:
HasRequired(r=> r.People).WithMany(p=>p.Relation).HasForeignKey(r=>r.ChildPeopleId);
So, how can I map the second foreign key?
Per each FK column in your Relations table you should have a navigation property in your Relation entity (this is not mandatory, but what is mandatory is have at least one navigation property between the entities involve in the relationship). In this case you have two relationships between People and Relations, and a navigation property represents one end in an relationship. Your model could be this way:
public class Relation
{
public int Id {get;set;}
public int ParentPeopleId {get;set;}
public int ChildPeopleId {get;set;}
public virtual People ParentPeople {get;set;}
public virtual People ChildPeople {get;set;}
}
public class People
{
public int Id {get;set;}
public string Name {get;set;}
public virtual ICollection<Relation> ParentRelations {get;set;}
public virtual ICollection<Relation> ChildRelations {get;set;}
}
And the Fluent Api configurations like this:
HasRequired(r=> r.ParentPeople ).WithMany(p=>p.ParentRelations ).HasForeignKey(r=>r.ParentPeopleId);
HasRequired(r=> r.ChildPeople).WithMany(p=>p.ChildRelations ).HasForeignKey(r=>r.ChildPeopleId );
Now if you don't want to work with one of the collection navigation properties in your People entity, you can create an unidirectional relationship. For example if you don't want ParenRelations navigation property, you can configure that relationship as follow:
HasRequired(r=> r.ParentPeople).WithMany().HasForeignKey(r=>r.ParentPeopleId);
Update
Let me start first with a suggestion. I thing your table Relation is not playing any role is you have only those columns. If a person con only have a parent I would change your model to the following:
public class People
{
public int Id {get;set;}
public string Name {get;set;}
public int ParentId {get;set;}
public virtual People Parent {get;set;}
public virtual ICollection<People> Children {get;set;}
}
And you relationship configuration would be:
HasOptional(r=> r.Parent).WithMany(p=>p.Children).HasForeignKey(r=>r.ParentId);
Now going back to your current model, EF sees your ChildPeopleId property as an simple scalar column, it doesn't know it's a FK column, that's way I suggested above map two relationship instead one.
Another thing, with the below line
var Peoplelist = MyDbContext.People.Include(p=>p.Relations.Select(r=>r.People)).ToList();
You are telling to EF that you want to load the Relation entities related to a People, but also you want to load the People related with each Relation, which is at the same time the same People where the Relation came from, so, you don't need to do the last select, if your data is properly related, that People navigation property is going to be loaded when you execute your query,so, that query should be this way:
var Peoplelist = MyDbContext.People.Include(p=>p.Relations).ToList();
I have an entity/class/table which is referenced from several other entities, and I use Fluent NHibernate to handle the ORM for me. In a few instances, it's a simple reference where I can store the foreign key ID as a column and handle the reference in that simple way, but in a few other instances I need to reference a list of these items, and it needs done for at least three classes I can think of. You can assume this setup will be copied to handle the other classes' relationships.
Here's how the common entity looks (the one that is owned by several other entities in HasManys):
public class Student {
public virtual int Id {get; set;}
public virtual string Name {get; set;}
}
And, here's what the ShopCourse entity looks like:
public class ShopCourse {
public virtual int Id {get; set;}
public virtual int Name {get; set;}
public virtual IList<Student> Students {get; set;}
}
Imagine that a couple other classes I have, such as specific courses, can "own" several students. In order to maintain that relationship I must create a table in my database that tracks the foreign keys between the two (for each entity that references Student) - no entity needed for this intermediate table, and Fluent won't need to think of it unless I hand it the string name of the table itself:
Table: ShopCourseStudents
int - ShopCourseId
int - StudentId
Lastly, here are my mappings. You can assume that the entities themselves map out fine - things such as the naming scheme for the Id are resolved and working correctly. The issue lies when I attempt to initialize any entity that has a HasMany of Student:
//Inside a FluentlyConfigure().Mappings(m => m.AutoMappings.Add() call:
.Override<ShopCourse>(map => {
map.HasMany(x => x.Students)
.Table("ShopCourseStudents")
.KeyColumns.Add("ShopCourseId")
.KeyColumns.Add("StudentId")
.Cascade.All();
})
The issue is that when I attempt to load a list of ShopCourses I get the Fluent error:
Foreign key (ABC123AF9:Student [ShopCourseId, StudentId]) must have
same number of columns as the referenced primary key (ShopCourses
[Id])
I do not override Fluent's mapping of Student as it's straightforward. For the purpose of this example, Student doesn't need to know which ShopCourses it belongs to, or any of the other courses that may own that particular Student record.
This seems like I'm doing something basic, wrong - what is it, exactly? Much obliged in advance!
So, the issue was with the custom code that I re-use with my projects, apparently the piece written to handle the ManyToMany convention is mostly broken. What I was looking for here was a ManyToMany relationship, not HasMany. The issue I had was that my code was forcing a reference on the child object (in this example, Student) to the parent, which I do not need and only complicates things. Removing that, and my ManyToMany then works:
.Override<ShopCourse>(map => {
map.HasManyToMany(x => x.Students)
.Table("ShopCourseStudents")
.ParentKeyColumn("ShopCourseId")
.ChildKeyColumn("StudentId")
.Cascade.All()
I have same type of tables
ProductCodeTable, CountrycodeTable etc
All have key, value as their fields
When I use entity frame work,
Can I have a single entity for all these tables such that I can formulate different queries to get data from different tables?
You can create a base class for all of them and create sub class for each entity
public abstract class LookUpEntity
{
[Key]
public int Key { get; set; }
[Required]
public string Value { get; set; }
}
[Table("ProductCodeTable")]
public class ProductCode : LookUpEntity
{
}
This way you can model the relationships also and later if you wanted to add specific properties to those look up entities with out affecting other entities.
You can create a view with a Union of all tables like this:
create view AllKeyTables as
SELECT 'Product' as table, Productkey as Key, nameProduct as name
FROM ProductCodeTable
UNION
SELECT 'Country' as table, CountryISO as key, CountryName as name
FROM CountrycodeTable
UNION
...
Then update EF model and check 'table' and 'key' fields as Entity Primary Key.
Next question you will do is: 'How can I make a relation between this Entity and existing Entities?' The answer is 'you can't because EF is not able to join Entities between other fields than primary key'. Then, before implement this solution, be sure that this is you are looking for.
EF supports this only if you model it as inheritance (#Eranga showed it in code-first approach). You will have single base entity and derived entity for each table so you will not avoid having different type for each table. Otherwise the answer is no.
Inheritance will put additional requirements on data in your tables. For example Ids will have to be unique among all tables. So if ProductTableCode will have record with Id 1, CountryCodeTable (and any other code table) mustn't have record with Id 1.
Also inheritance in EF can produce nasty and very poorly performing queries.
I want to create following table based on below class dictionary. I get exception when I add records. What's wrong with this mapping? This code works if I point Child property of class "B" to another class (example "C").
database table
table A {id, name}
table B {parentId, childId, Type}
Class and Mapping
Public class A
{
public int Id {get;set;}
public string Description {get;set;}
}
Public class B
{
[Key, Column(Order=0)]
public int ParentId {get;set;}
[Foreignkey("ParentId")]
public A Parent {get;set;}
[Key, Column(Order=1)]
public int ChildId {get;set;}
[Foreignkey("ChildId")]
public A Child {get;set;}
[Key, Column(Order=2)]
public string Type {get;set;}
}
UPDATE
Error Message is: Introducing FOREIGN KEY constraint 'B_Parent' on table 'B' 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.
Thanks,
Ashraf
After reading the following posts I found the solution.
http://weblogs.asp.net/manavi/archive/2011/05/01/associations-in-ef-4-1-code-first-part-5-one-to-one-foreign-key-associations.aspx
Entity Framework Code First - Defining Relationships/Keys
It's the SQL Server error. Class 'A' referencing twice in class 'B'. Code First attempt to turn on cascade delete for both Parent and Child columns in class 'B' which cause the exception.
Fix is manually override one of the cascade option to false in class B. I don't know how to set CascadeOnDelete option as dictionary attribute. But here is the fluent api.
HasRequired(x => x.Parent)
.WithMany()
.HasForeignKey(x => x.ParentId)
.WillCascadeOnDelete(false);
I wish EF team attempt to write a comprehensive guide for Code First configuration (Fluent API) manual for us. AdventureWorks-2008 database is a great candidate for that.
this exception is SQL server specific.It will go away if you turn off the cascade for the relationship.By default Ef will turn it on for you.you can do this through fluent api.
In the relationship just add the following configuration
.WillCascadeOnDelete(false);
hope this helps.
This is the basic example from hbm-style nhibernate.
http://ayende.com/blog/2327/multi-table-entities-in-nhibernate
public class Person
{
public int PersonId {get;set;}
public string Name {get;set;}
public string AddressStreetAddress {get;set;}
public string AddressZipCode {get;set;}
}
In the database, Person has an Id primary key, a name field, and an address foreign key. Address has its own primary key, a street address field and a zip code field.
The correct answer is "Don't do it.". Unfortunately I'm stuck with an entity object that exposes the Id and Name of another entity and those are used elsewhere still. At the moment, this object won't be persisted back to the database through nHibernate.
I think the way to do this is to use the address as the table of the entity and add the Person fields from the Join(). What are the consequences of doing this as an intermediate step in a change-over?
I think the way to do this is to use
the address as the table of the entity
and add the Person fields from the
Join(). What are the consequences of
doing this as an intermediate step in
a change-over?
This was a bad idea because the only Id you could map to is the Id of the address which can be shared between multiple persons.
Instead, add a private/protected property for Address to Person, map Address and reference the address using the following Fluent call.
References(Reveal.Member<Person, Address>("Address")).Column("address_id")
Then, you can use AddressStreetName and AddressZipCode to pass through to Address.StreetName and Address.Zipcode. After that, it's a simple matter of refactoring the rest of the system to be sane again.