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.
Related
With MVC 5 and EF 6.1 I am using a simple inheritance hierarchy, where class Student inherits from class Person. For both classes I have an entity set (DbSet property) in my database context:
public class DatabaseContext : DbContext
{
public DbSet<Person> Persons { get; set; }
public DbSet<Student> Students { get; set; }
}
Now when I ask the scaffolder to generate a controller for Student, the subclass, it uses the Persons entity set, leading to statements such as
Student student = db.Persons.Find(id);
where the compiler obviously complains that it cannot just convert any Person to a Student.
Is there a way to make sure that the scaffolder uses the correct entity set (Students in this case)?
Note that removing the Persons entity set is not a good solution, because there are other controllers that need that.
Use find and replace to change all occurrences in the Controller class of the parent DBSet to the child DBSet eg change Persons to Students.
As you probably know (as I think you raised it) Microsoft have confirmed this is a known bug http://connect.microsoft.com/VisualStudio/feedbackdetail/view/945937/mvc-5-scaffolding-with-inheritance-uses-the-wrong-entity-set but they won't be fixing it.
Instead of inheritance why not use a relationship making personID the Foreign key ? That why you can db.students.find(personID)
And
db.person.find(personID)
To find all details ?
Extra code but I can't think of another way
You can use the command OfType<>, as shown:
Student student = db.Persons.OfType<Student>().SingleOrDefault(s => s.id == id);
This command works with inheritance. In this case, when Student inherits from Person.
I have db scheme where Product table have many to many relation to Color table. I'm using EF and create POCO objects:
public class Product
{
public Guid Id {get;set;}
public ICollection<Color> Colors {get;set;}
}
public class Color
{
public Guid Id {get;set;}
public ICollection<Product> Products {get;set;}
}
In many situations it is necessary to delete all colors related to product and set new colors. So i want to delete all many to many relations whitout exactly knowing id of related colors. Is it possible to delete them without additional queries to db? I know i can just write stored procedure which will delete all relation with colors for specified product, but it will be better to find general approach through entity framework.
If you don't know keys of colors you cannot delete them without loading them first - EF deletes records one by one so it needs to know which record to delete.
The straight forward option is executing SQL DELETE directly:
dbContext.Database
.ExecuteSqlCommand("DELETE FROM dbo.ProductColors WHERE ProductId = #Id", product.Id);
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()
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.
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.