I have something like this:
public class Person {
string Name;
}
public class Customer : Person {
List<Order> orders;
}
public class MyReference {
Person aPerson;
}
public class Me {
MyReference myRef;
}
Now in my Metamodel I have specified a baseType for Customer. And I think my metamodel is right. The only problem is, that when I want to execute a query like the following:
breeze.EntityQuery.from('Me').expand('myRef, myRef.aPerson, myRef.aPerson.orders')
I get an error, that "orders" is not allowed on the EntityType "Person". Of course as it's the base-class. I would like it to be polymorphic and if the Person is really of Type "Customer" it should expand orders and if not, well then it can be empty or not defined or not even existent on the object.
Is this somehow possible? Would I need some kind of "toType" to cast inside the Query?
The base class, Person, does not have an Orders property. Therefore, .NET (EF) on the server won't let you ask for Person.Orders. That's not how polymorphism works in EF and there isn't anything Breeze can do to change that.
You'll need a different approach I'm afraid.
FWIW, that isn't how polymorphism works in Breeze either.
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 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'm having difficulties retrieving relationships when the relationship type is annotated with a #RelationshipType field.
The relationships look correct in Neoclipse, but I'm retrieving no results in my application.
The code that doesn't work is (simplified):
#NodeEntity
public abstract class Entity {
#RelatedToVia
private Collection<Relationship> relationships;
public Relationship relatedTo(Entity entity, String type) {
Relationship relationship = new Relationship(type, this, entity);
relationships.add(relationship);
return relationship;
}
...
}
and:
#RelationshipEntity
public class Relationship {
#RelationshipType
private String type;
...
}
The code that does work is:
#RelationshipEntity(type = "something")
public class Relationship {
...
}
However, this doesn't suit my use case (I have a bunch of different Relationship types between arbitrary combinations of Entity instances.
The full test code is below. Agency and Item are both subclasses of Entity.
// Create first entity
Agency arnz = agencyRepository.save(new Agency());
arnz.setCode("ARNZ");
agencyRepository.save(arnz);
// Create second entity
Item r123 = itemRepository.save(new Item());
r123.setCode("R123");
// Create parent/child relationship between entities
r123.relatedTo(arnz, EntityRelationshipType.PARENT);
itemRepository.save(r123);
// Retrieve entity from database
Entity entity = itemRepository.findByCode("R123");
// Verify that relationship is present
assertThat(entity.getRelationships().iterator().hasNext(), is(true));
The final line is where the test is failing. Any clues?
M
PS. I'm a rank amateur with Neo4j and just happened to find #RelationshipType, so I may well be doing something laughably wrong. I hope so!
Sorry to disappoint you, but during the retrieval the code right now doesn't look for the type class but rather for the type from #RelatedToVia or #RelationshipEntity or the field name relationships as relationship-type. But you're making a valid point, can you please raise in issue in JIRA?
Did you look into template.getRelationshipsBetween ?
Why don't you create individual classes for your relationships? What is the use-case for this approach?
Suppose I want to allow to select our entity (from a dropdown, etc) on a page, let's say Product. As a result I may receive this:
public ActionResult SelectedAction(Guid productId)
{
}
But, I want to use model binders power, so instead I write model binder to get my product from repository and instead use
public ActionResult SelectedAction(Product product)
{
if (ModelState.IsValid) {} else {}
}
My model binder will set model state to false if product is invalid.
Now, there're problems with this approach:
It's not always easy to use strongly-typed methods like Html.ActionLink(c => c.SelectedAction(id)) since we need to pass Product, not id.
It's not good to use entities as controller parameters, anyway.
If model state is invalid, and I want to redirect back and show error, I can't preserve selected product! Because bound product is not set and my id is not there. I'd like to do RedirectToAction(c => c.Redisplay(product)) but of course this is not possible.
Now, seems like I'm back to use "Guid productId" as parameter... However, there's one solution that I'd like to present and discuss.
public class EntityViewModel<T> where T : BaseEntity
{
public EntityViewModel(Guid id)
{
this.Id = id;
}
public static implicit operator EntityViewModel<T>(T entity)
{
return new EntityViewModel<T>(entity.Id);
}
public override string ToString()
{
return Id.ToString();
}
public Guid Id { get; set; }
public T Instance { get; set; }
}
Now, if I use
public ActionResult SelectedAction(EntityViewModel<Product> product)
{
if (ModelState.IsValid) {} else {}
}
all the problems are solved:
I can pass EntityViewModel with only Id set if I have only Id.
I don't use entity as parameter. Moreover, I
can use EntityViewModel as property inside another ViewModel.
I can pass EntityViewModel back to RedirectToController and it will keep its Id value, which will be
redisplayed to user along with the validation messages (thanks to MVCContrib and ModelStateToTempData / PassParametersDuringRedirect).
The model binder will get Instance from the repository and will set model state errors like "Not found in database" and so on. And I can use things like ActionLink(c => c.Action(Model.MyProductViewModelProperty)).
The question is, are there any drawbacks here? I can't see anything bad but I'm still new to MVC and may miss some important things. Maybe there're better and approved ways? Maybe this is why everybody uses entity IDs as input parameters and properties?
Overall that looks like a good appoach to me...
As an alternative, you could use POCO for your viewmodel then I think all 3 problems would be solved automatically. Have you seen the Automapper project that allows an Entity to DTO approach? This would give you more flexibility by separating you ViewModel from your EntityModel, but really depends on the complexity of you application you are building.
MVC's ViewDataExtensions might also be useful instead of creating custom containers to hold various viewmodel objects as you mention in number 2.
MVCContrib's ModelStateToTempData should work for any serializable object (must be serializable for any out of process sessionstate providers eg. SQL, Velocity etc.), so you could use that even without wrapping your entity classes couldn't you?
Let's say I have two tables employee and salary with a 1:N relationship (one salary can be associated with many employees).
In plain SQL the tables would be joined with:
SELECT e.id, e.name, s.salary FROM employee e, salary s WHERE s.id = e.salary_id AND e.id = 12345;
Assuming the following GORM-powered domain class how do I map the legacy database structure to the class?
class Employee {
String name
int salary
}
Clarification #1: I want only one domain class containing data from both tables. Adding another class is hence not an option.
Clarification #2: The question I'm trying to find an answer to is simply "how do I map two tables to one class using Grails/GORM"? If you believe that it is impossible to do so, then please state that clearly in your answer rather than trying to restate the question.
IMO it is not possible with plain Grails/GORM to join multiple tables and map them to one Domain class. As a workaround you could use a legacy XML hibernate mapping and leverage the join feature to achieve your desired goal. Of course you would loose a lot of the GORM goodies.
Your SQL example indicates there are two tables, Employee and Salary. This should also be reflected in your classes. So instead of one, you need two classes. The GORM mapping would then look like this.
class Employee {
String name
Salary salary
}
class Salary {
static hasMany = [ employees : Employee ]
int salary
}
See http://www.grails.org/GORM+-+Defining+relationships
You could, instead of having salary and name as properties, have them as get* methods that actually run a query on both these tables.
granted, that isnt the grails way, and its strongly recommended that you do follow the grails way.
I don't fully understand the limitation on not being able to add another class if there are 2 tables in the database, but if you're looking to have a unified interface, would it work to delegate the methods to the Salary class?
Something like:
class Salary {
int amount
}
class Employee {
Salary _salary
String name
String toString() { name }
public Integer getSalary() {
return _salary?.amount
}
public void setSalary(Integer amount) {
// not quite sure of your business logic here, this is a guess
_salary = Salary.findByAmount(amount)
if (!_salary) {
_salary = new Salary(amount: amount)
_salary.save()
}
}
}
def e = new Employee(name:"willy loman", salary: 100)
e.save()
assert e.salary == 100
It's also possible that you might be able to make what you're asking for work with a custom hibernate mapping file, but I'm not familiar enough with contorting hibernate in that manner to say for sure.
See the Custom User Type section of this page.