I've been looking into the specification pattern for my repositories, I'm using EF4 inside my repositories to query the database and map the selected entities by passing in an expression, something like this:-
public IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> predicate)
{
return _objectSet.Where<TEntity>(predicate);
}
This works okay if your just working with the one object set but say if you wanted to select all the comments made by a user that are greater than 128 chars and the user is active. How would you create a specification when two or more object sets are used?
Example:-
class User
{
public string Name { get; set; }
public bool Active { get; set; }
public virtual ICollection<Post> Posts { get; set; }
public User()
{
Posts = new List<Post>();
}
}
class Post
{
public string Text { get; set; }
public DateTime Created { get; set; }
public virtual ICollection<Comment> Comments { get; set; }
public Post()
{
Comments = new List<Comment>();
}
}
class Comment
{
public string Text { get; set; }
public DateTime Created { get; set; }
}
To do this in Linq is :-
var results = from u in users
from p in u.Posts
from c in p.Comments
where u.Active && c.Text.Length > 128
select c;
How would you then convert that to a specification class? Maybe I am just not seeing something as it seems like a reasonable thing to do :)
EDIT
The specification interface:
public interface ISpecification<TEntity>
{
bool IsSatisfiedBy(TEntity entity);
}
First of all your current setup doesn't allow such query because User and Comment are not related. You can select only all comments related to posts related to user but you don't know who posted comments.
Just add relation between User and Comment and you can simply use:
var results = from c in context.Comments
where c.User.Active and c.Text.Length > 128
select c;
This will be easily possible in your Specification pattern. Anyway if you want to build complex condition from Comment in your Find method you must expose navigation properties to allow that.
Funny I was just reading about OCP (Open Closed Principle) and the Specification pattern, and I was wondering whether it's actually worth implementing the Specification pattern in my project. I'm just worried I might end up with a huge pile of specifications due to the fact that I have several entities and I query by several criteria.
Anyway, here's one (actually two) of my favorite blog posts about the patterns you're using (which I'm using as well):
Entity Framework 4 POCO, Repository and Specification Pattern
Specification Pattern In Entity Framework 4 Revisited
Related
I'm currently writing an ASP .NET Core API utilizing OData for querying, and Entity Framework to talk to the database.
I want to separate the domain objects from the DTOs sent to the user, so have also started to use AutoMapper to translate entity framework query results to DTOs I have created.
At this point (while I'm testing), my DTOs and domain objects are the same - just public getter/setter properties. Examples of the DTOs are as follows:
public class NoteDTO
{
public int Id { get; set; }
public string Body { get; set; }
public string Conclusion { get; set; }
public string Title { get; set; }
public ManagerDTO Manager { get; set; }
}
public class ManagerDTO
{
public int Id { get; set; }
public virtual List<ProductDto> Products { get; set; }
}
public class ProductDto
{
public int Id { get; set; }
}
I also have a test method in my NotesController for fetching notes (again, using OData) which is as follows:
[HttpGet]
[EnableQuery]
public IQueryable<NoteDTO> GetMeeting()
{
var config = new MapperConfiguration(cfg =>
{
cfg.CreateMap<Note, NoteDTO>();
cfg.CreateMap<Product, ProductDto>();
cfg.CreateMap<Manager, ManagerDTO>()
.ForMember(md => md.Products, conf => conf.MapFrom(m => m.Products));
});
return _context.Notes.ProjectTo<NoteDTO>(config);
}
I then try and hit my API with the following query:
https://localhost:5001/api/Notes?$select=Id,Body,Conclusion&$top=5&$expand=Manager($select=Id)
However, this fails, and in amongst the stack trace, I'm given the following error message:
System.ArgumentException: Expression of type 'System.Collections.Generic.IEnumerable`1[System.Tuple`3[TestEntityFramework.DataObjects.ProductDto,Microsoft.EntityFrameworkCore.Query.Internal.MaterializedAnonymousObject,Microsoft.EntityFrameworkCore.Query.Internal.MaterializedAnonymousObject]]' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable`1[TestEntityFramework.DataObjects.ProductDto]' of method 'System.Collections.Generic.IEnumerable`1[TestEntityFramework.DataObjects.ProductDto] _ToEnumerable[ProductDto](System.Collections.Generic.IEnumerable`1[TestEntityFramework.DataObjects.ProductDto])'
If I remove the List from the ManagerDTO object and the relevant Product mapping config, the query above works successfully.
I saw this comment on a GitHub issue for what sounds like the same problem, but trying to implement the suggestion hasn't helped (assuming I've understood them correctly): https://github.com/AutoMapper/AutoMapper/issues/2853#issuecomment-482317381
Has anyone else run into this problem? I'm still getting used to AutoMapper so may have missed something obvious, but from searching around this seems to be a fairly uncommon issue and so pointers as to what's going on here have been hard to come by.
I'm open to any other suggestions as to what the best way of translating an OData query to entity framework, then back to a DTO is as well - if what I'm doing here isn't optimal!
Are you using the Automapper Collection Extensions? If not, this should solve your problem: https://github.com/AutoMapper/AutoMapper.Collection
Let me foreword this by saying this is my first real experience with both Entity Framework and relational databases in general. If I am doing it completely wrong, please tell me.
I want my data structured as something like this (Cut down on the "extra" code):
Indicators {
int SomeText1TranslationRef
List<Translation> SomeText1Translations
int SomeText2TranslationRef
List<Translation> SomeText2Translations
}
Measures {
int SomeText3TranslationRef
List<Translation> SomeText3Translations
int SomeText3TranslationRef
List<Translation> SomeText4Translations
}
Translation {
Int TranslationID
String LanguageCode
String Text
}
So in essence, the indicators table would have a list of SomeText1 Translations as well as SomeText2, all joined using the TranslationID through the "Ref" properties.
I have the translation properties annotated with [ForeignKey("....Ref")].
I expected this to work magically as the rest of the framework seems to, but instead the translation table gets columns named "SomeText1TranslationRef" and "SomeText2TranslationRef".
Am I doing this wrong?
I am looking at other features of Entity Framework and see an annotation for "InverseProperty". Is it something which may help?
I'm not 100% clear on your goal, but if an Indicator can have many Text1 translations and many Text2 translations, then that is 2 many-to-many relationships. Same for Measures. EF will need a join/bridge/junction table for this (IndicatorTranslation and MeasureTranslation). You can explicitly create this table, or let EF do it behind the scenes:
Indicator {
// other indicator fields
public virtual List<Translation> SomeText1Translations
public virtual List<Translation> SomeText2Translations
}
Measure {
// other measure fields
public virtual List<Translation> SomeText3Translations
public virtual List<Translation> SomeText4Translations
}
Translation {
Int TranslationID
String LanguageCode
String Text
// Use inverse attributes or fluent code to tell EF how to connect relationships
[InverseProperty("SomeText1Translations")]
public virtual ICollection<Indicator> TranslationForIndicatorText1 { get; set; }
[InverseProperty("SomeText2Translations")]
public virtual ICollection<Indicator> TranslationForIndicatorText2 { get; set; }
[InverseProperty("SomeText3Translations")]
public virtual ICollection<Measure> TranslationForMeasureText3 { get; set; }
[InverseProperty("SomeText4Translations")]
public virtual ICollection<Measure> TranslationForMeasureText4 { get; set; }
}
I'm happy to be corrected if I'm wrong since it's nothing I've tried for quite a while, but as far as I'm aware, EF is still not able to create relationships from one property on a type to two different other types, or vice versa, even with constraints that would make it valid.
In your case, you would end up with the 4 navigation properties being required on your translation. (int IndicatorRef1, int IndicatorRef2, int MeasureRef3, int MeasureRef4). Most wouldn't call it a dream scenario.
I asked a similar question a couple of years ago, and have since then sort of concluded that i was foolish trying to get EF to solve all my problems.
So here's an answer to what you're trying to achieve, and perhaps even a solution to 2 of your questions:
Don't rely on EF handle any scenario. Actually, pretty much don't rely on EF to handle relationships at all other than 1-1, 1-* or *-*. And some forms of inheritance.
In most other cases, you will end up with one navigation property for each type you're trying to reference, with data being populated with nulls for each navigation property but the one specifically targeted.
The good news? You don't have to rely on EF for it. The main advantage of EF is it's productivity. For certain cases, it's still worth leveraging EF, but providing your own methods of productivity. If you want to get a set of indicators with 2 collections of translations based on a ref, simply create a method that provides it.
Something like
public IQueryable<Indicators> SetOfIndicatorsWithTranslations()
{
// Untested query that might need some fixing in an actual implementation
return ctx.Set<Indicators>().Select(ind => new Indicators() {
Text1Ref= ind.Text1Ref, // whatever the property is
Text1RefList = ctx.Set<Translation>().Where(t => t.TranslationId == ind.Text1Ref),
Text2Ref= ind.Text2Ref,
Text2RefList = ctx.Set<Translation>().Where(t => t.TranslationId == ind.Text2Ref),
});
}
Now that's a query EF will handle for you gracefully.
There are of course a lot more elegant solutions to something like it. The important part is really that it's sometimes worth doing it yourself rather than restricting yourself to the capabilities of your tool of choice. (Well, at least that's the important part that I eventually learned :) )
Long story short, the caveat is the "Core" part of .Net Core. EF Core does not support convention-over-configuration many-to-many relationships yet (See here).
The only way to achieve this is to manually create the junction tables as Steve suggested. Here is all the information needed: https://www.learnentityframeworkcore.com/configuration/many-to-many-relationship-configuration
In previous versions of Entity Framework, this model definition was sufficient for EF to imply the correct type of relationship and to generate the join table for it. In EF Core 1.1.0, it is necessary to include an entity in the model to represent the join table, and then add navigation properties to either side of the many-to-many relations that point to the join entity instead:
The above link will most likely be updated with time so for context purposes, here is the code which goes along with it:
public class Book
{
public int BookId { get; set; }
public string Title { get; set; }
public Author Author { get; set; }
public ICollection<BookCategory> BookCategories { get; set; }
}
public class Category
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
public ICollection<BookCategory> BookCategories { get; set; }
}
public class BookCategory
{
public int BookId { get; set; }
public Book Book { get; set; }
public int CategoryId { get; set; }
public Category Category { get; set; }
}
Alternatively, using Fluent:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.Entity<BookCategory>()
.HasKey(bc => new { bc.BookId, bc.CategoryId });
modelBuilder.Entity<BookCategory>()
.HasOne(bc => bc.Book)
.WithMany(b => b.BookCategories)
.HasForeignKey(bc => bc.BookId);
modelBuilder.Entity<BookCategory>()
.HasOne(bc => bc.Category)
.WithMany(c => c.BookCategories)
.HasForeignKey(bc => bc.CategoryId);
}
I am testing Knockout 2.1.0 and Upshot 1.0.0.2 with Entity Framework 4.3 (Code-First) and am running into the following error:
{"Object graph for type
'System.Collections.Generic.HashSet`1[[KnockoutTest.Models.Person,
KnockoutTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'
contains cycles and cannot be serialized if reference tracking is
disabled."}
I am using a fairly typical model for testing with some basic parent-child entities.
public class Client
{
public Client()
{
Projects = new HashSet<Project>();
Persons = new HashSet<Person>();
}
[Key]
public int ClientId { get; set; }
[Required]
[Display(Name = "Client Name", Description = "Client's name")]
[StringLength(30)]
public string Name { get; set; }
public ICollection<Project> Projects { get; set; }
public ICollection<Person> Persons { get; set; }
}
public class Project
{
public Project()
{
}
[Key]
public int ProjectId { get; set; }
[StringLength(40)]
public string Name { get; set; }
public int? ClientId { get; set; }
public virtual Client Client { get; set; }
}
public class Person
{
public Person()
{
PhoneNumbers=new HashSet<PhoneNumber>();
}
[Key]
public int PersonId { get; set; }
[Required]
[Display(Name="First Name", Description = "Person's first name")]
[StringLength(15)]
public string FirstName { get; set; }
[Required]
[Display(Name = "First Name", Description = "Person's last name")]
[StringLength(15)]
public string LastName { get; set; }
[ForeignKey("HomeAddress")]
public int? HomeAddressId { get; set; }
public Address HomeAddress { get; set; }
[ForeignKey("OfficeAddress")]
public int? OfficeAddressId { get; set; }
public Address OfficeAddress { get; set; }
public ICollection<PhoneNumber> PhoneNumbers { get; set; }
public int? ClientId { get; set; }
public virtual Client Client { get; set; }
}
public class Address
{
[Key]
public int AddressId { get; set; }
[Required]
[StringLength(60)]
public string StreetAddress { get; set; }
[Required]
[DefaultValue("Laurel")]
[StringLength(20)]
public string City { get; set; }
[Required]
[DefaultValue("MS")]
[StringLength(2)]
public string State { get; set; }
[Required]
[StringLength(10)]
public string ZipCode { get; set; }
}
public class PhoneNumber
{
public PhoneNumber()
{
}
[Key]
public int PhoneNumberId { get; set; }
[Required]
[Display(Name = "Phone Number", Description = "Person's phone number")]
public string Number { get; set; }
[Required]
[Display(Name = "Phone Type", Description = "Type of phone")]
[DefaultValue("Office")]
public string PhoneType { get; set; }
public int? PersonId { get; set; }
public virtual Person Person { get; set; }
}
My context is very generic.
public class KnockoutContext : DbContext
{
public DbSet<Client> Clients { get; set; }
public DbSet<Project> Projects { get; set; }
public DbSet<Person> Persons { get; set; }
public DbSet<Address> Addresses { get; set; }
public DbSet<PhoneNumber> PhoneNumbers { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
}
}
I also have a little bit of sample data--though it should not be relevant.
protected override void Seed(KnockoutContext context)
{
base.Seed(context);
context.Clients.Add(new Client
{
Name = "Muffed Up Manufacturing",
Persons = new List<Person> {
new Person {FirstName = "Jack", LastName = "Johnson",
PhoneNumbers = new List<PhoneNumber>
{
new PhoneNumber {Number="702-481-0283", PhoneType = "Office"},
new PhoneNumber {Number = "605-513-0381", PhoneType = "Home"}
}
},
new Person { FirstName = "Mary", LastName = "Maples",
PhoneNumbers = new List<PhoneNumber>
{
new PhoneNumber {Number="319-208-8181", PhoneType = "Office"},
new PhoneNumber {Number = "357-550-9888", PhoneType = "Home"}
}
},
new Person { FirstName = "Danny", LastName = "Doodley",
PhoneNumbers = new List<PhoneNumber>
{
new PhoneNumber {Number="637-090-5556", PhoneType = "Office"},
new PhoneNumber {Number = "218-876-7656", PhoneType = "Home"}
}
}
},
Projects = new List<Project>
{
new Project {Name ="Muffed Up Assessment Project"},
new Project {Name ="New Product Design"},
new Project {Name ="Razor Thin Margins"},
new Project {Name ="Menial Managerial Support"}
}
}
);
context.Clients.Add(new Client
{
Name = "Dings and Scrapes Carwash",
Persons = new List<Person> { new Person {FirstName = "Fred", LastName = "Friday"},
new Person { FirstName = "Larry", LastName = "Lipstick" },
new Person { FirstName = "Kira", LastName = "Kwikwit" }
},
Projects = new List<Project>
{
new Project {Name ="Wild and Crazy Wax Job"},
new Project {Name ="Pimp Ride Detailing"},
new Project {Name ="Saturday Night Special"},
new Project {Name ="Soapy Suds Extra"}
}
}
);
IEnumerable<DbEntityValidationResult> p = context.GetValidationErrors();
if (p != null)
{
foreach (DbEntityValidationResult item in p)
{
Console.WriteLine(item.ValidationErrors);
}
}
}
}
Basically, whenever I attempt to use an "Include" from Client, Person, Project, etc. I get a similar error to the one listed above.
namespace KnockoutTest.Controllers
{
public class ClientController : DbDataController<KnockoutTest.Models.KnockoutContext>
{
public IQueryable<Client> GetClients()
{
return DbContext.Clients.Include("Persons").OrderBy(o => o.Name);
}
}
public class ProjectController : DbDataController<KnockoutTest.Models.KnockoutContext>
{
public IQueryable<Project> GetProjects()
{
return DbContext.Projects.OrderBy(o => o.Name);
}
}
public class PersonController : DbDataController<KnockoutTest.Models.KnockoutContext>
{
public IQueryable<Person> GetPersons()
{
return DbContext.Persons.Include("Client").OrderBy(o => o.LastName);
}
}
public class AddressController : DbDataController<KnockoutTest.Models.KnockoutContext>
{
public IQueryable<Address> GetAddresses()
{
return DbContext.Addresses.OrderBy(o => o.ZipCode);
}
}
public class PhoneNumberController : DbDataController<KnockoutTest.Models.KnockoutContext>
{
public IQueryable<PhoneNumber> GetPhoneNumbers()
{
return DbContext.PhoneNumbers.OrderBy(o => o.Number);
}
}
}
Can you see any reason why .NET should be complaining about this model?
Regardless, what options do I have to work around it?
Thank you for any assistance!
The short answer is that Steve Sanderson's demonstration of Knockout, Upshot, and Entity Framework 4.x Code-First to build a Single Page Application was (while great!!!) maybe a little misleading. These tools do not play nearly as nicely together as they appear at first glance. [Spoiler: I do believe there is a reasonable workaround but it involves stepping outside of the Microsoft arena ever-so-slightly.]
(For Steve's fantastic Single Page Application (SPA) presentation, please visit http://channel9.msdn.com/Events/TechDays/Techdays-2012-the-Netherlands/2159. It is well worth a watch.)
In most any Web application, We conceptually need to move and manipulate data in the following way:
Data Source (often a Database) -> Web Application -> Browser Client
AND
Browser Client -> Web Application -> Data Source (often a Database)
In the past, manipulating data to receive it from and transmit it to the database was a real nightmare. If you have to be around in the .NET 1.0/1.1 days, you may recall a development process that included steps like:
Manually defining a data model
Creating all of the tables, setting up relationships, manually defining indexes and constraints, etc.
Creating and testing stored procedures to access the data - generally manually specifying each field to be included in each procedure.
Create POCO (Plain Old CLR Objects) to hold the data
Code to open a connection to the database and iteratively recurse each record returned and map it into the POCO objects.
This was just to get the data into the system. Going back the other way we had to repeat several of these steps in reverse order. The point is that database coding was very time consuming (and really quite boring). Obviously, a number code generation and other tools came along and simplified things.
The real breakthroughs were with NHibernate, Entity Framework 4 (Code-First approach), and other similar ORM tools which (almost) completely abstracted the database from the developer. These tools not only increased development speed, but also improved overall code quality since their were fewer opportunities to mistakenly introduce bugs.
Now, in many applications, connectivity to and interaction with a database is (almost) an afterthought since most database details are hidden away.
Microsoft has also provided Upshot.js and the WebAPI with the idea that these two tools, when used in conjunction with one another, are going to revolutionize the communication between the server and the browser in the same way that NHibernate and Entity Framework 4 have done between the server and the database.
This would indeed be a very worthy accomplishment--especially as clients are pushing for more interactive Web applications.
One of the main stumbling blocks that prevents developers from moving more of the user interface to the (browser) client is the significant amount of coding required. Some of the steps include:
Transmit the data to the client (usually in JSON format)
Map all of the properties from the .NET objects into JavaScript objects
Re-create all of the meta-data about the object and its properties
Bind that data to the elements in the client browser
Monitor changes
Re-map the data (for sending back to the server) once it has been modified
Transmit the data back to the server
This really seems quite like "deja vu" because it is quite similar in complexity to the legacy processes for getting data into and out of a database.
Depending on how the Web application is configured, there may be additional fun mapping the data once it returns to the server to actual database objects. (This will be the case more often than not.)
This server->client->server data transmission requires a lot of coding and offers many opportunities for unexpected challenges Don't forget how much fun it is to debug JavaScript! (Ok, it's less painful now than it was a couple of years ago, but it is still not as developer-friendly as debugging C# code in Visual Studio.)
Steve Sanderson's presentation on Single Page Applications offers a far different (and better) solution.
The idea is that WebAPI, Upshot.js, and Knockout would be able to seamlessly deliver data to and receive data from a browser client while providing a highly interactive user experience. Wow! Doesn't that make you just want to reach out and hug someone?
While this idea is not new, it is one of the first serious efforts I think have seen to really do this in .NET.
Once the data is delivered through the WebAPI and reaches the client (via Upshot), then frameworks like Knockout would be able to consume the data and deliver the very high level of interactivity cutting edge Web applications require. (While it may not be immediately clear, what I describing are applications which do not primarily function by loading "pages" but rather by primarily communicating JSON formatted data through AJAX requests.)
Any tool that cuts down on all of this coding is obviously going to be quickly embraced by the developer community.
Upshot.js (the renamed and upgraded version of RIA/JS) was supposed to take care of several of the mundane tasks listed above. It is supposed to be the glue between the WebAPI and Knockout. It is intended to dynamically map objects which are tansmitted in JSON or XML from .NET and also expose the associated meta-data for things like object properties, required fields, field lengths, display names, descriptions, etc. (The meta-data is what allows the mapping and MAY be accessed for use in validation.)
Note: I am still uncertain how to access the upshot meta-data and tie it to a validation framework like jQuery validation or one of the Knockout validation plugins. This is on my todo list to test.
Note: I am uncertain which of these types of meta-data are supported. This is on my todo list to test. As a side note, I also plan to experiment with meta-data outside of System.ComponentModel.DataAnnotations to also see if NHibernate attributes are supported as well as custom attributes.
So with all of this in mind, I set out to use the same set of technologies that Steve used in his demo in a real-world Web application. These included:
Entity Framework 4.3 using Code-First approach
ASP.NET MVC4 with WebAPI
Upshot.js
Knockout.js
The expectation is that all of these technologies would function well together because a) they are the latest Microsoft tools (with the exception of the open source Knockout) and because Steve Sanderson, currently of Microsoft, used them together in major Microsoft presentation demonstrating the development of single page application.
Unfortunately, what I found in practice was that Entity Framework 4.x and Upshot.js view the world in very different ways and their orientations are somewhat more contradictory than complementary.
As mentioned, Entity Framework Code First does a really fantastic job allowing developers to define highly functional object models which it near-magically translates into a functional database.
One of the great features of Entity Framework 4.x Code First is the ability to navigate from a parent object to a child AND navigate from a child object back to its parent. These two-way associations are a cornerstone of EF. They save a tremendous amount of time and greatly simplify development. Moreover, Microsoft has repeatedly touted this functionality as great reason to use Entity Framework.
In Scott Guthrie's, blog post (http://weblogs.asp.net/scottgu/archive/2010/07/16/code-first-development-with-entity-framework-4.aspx) where he initially introduced and explained EF 4 Code First approach, he demonstrates the concept of two-way navigation with the following two classes:
public class Dinner
{
public int DinnerID { get; set; }
public string Title { get; set; }
public DateTime EventDate { get; set; }
public string Address { get; set; }
public string HostedBy { get; set; }
public virtual ICollection<RSVP> RSVPs { get; set; }
}
public class RSVP
{
public int RsvpID { get; set; }
public int DinnerID { get; set; }
public string AttendeeEmail { get; set; }
public virtual Dinner Dinner { get; set; }
}
As you can see, Dinner contains an association with RSVPs AND RSVPs contains an association to Dinner. There are countless other examples of this on the Internet occurring in many variations.
Because these two way associations are such a core feature of Entity Framework, a reasonable person might expect that Microsoft would support this functionality in the library (Upshot.js) it uses to bring data from a .NET server application to the client. If the functionality was not supported, that is likely something they would want to share as it would significantly key architectural decisions and would most like not work with any properly designed EF 4 Code First implementation.
In my test code (listed in the original question above), I naturally assumed normal EF Code-First functionality (like two-way binding/navigation) was supported because that is what the presentation appeared to show.
However, I immediately started receiving nasty little run-time errors like:
"Object graph for type
'System.Collections.Generic.HashSet`1[[KnockoutTest.Models.Person,
KnockoutTest, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'
contains cycles and cannot be serialized if reference tracking is
disabled."
I tried numerous different approaches to try and fix the problem. Based on my ideas and my reading, here are a few of the failed solutions I attempted.
Removed the association from one side of the relationship. This is NOT a good solution because it is very handy to be able navigate in each direction between parent and child. (This is probably why these associative properties are referred to as navigation properties.) Remove the relationship from either side had side effects. When the relationship was removed from the parent, the ability to navigate a list of children was also removed. When the relationship was removed from the child, .NET provided me with another friendly error.
"Unable to retrieve association information for association
'KnockoutTest.Models.Client_Persons'. Only models that include foreign
key information are supported. See Entity Framework documentation for
details on creating models that include foreign key information."
Just in case the issue was the result of the system becoming confused about there being a foreign key, I explicitly specified a [ForeignKey] attribute on the child entity. Everything compiles but .NET returns the "Object graph for type... contains cycles and cannot be serialized..."
Some of my reading indicated that adding an attribute like [DataContract(IsReference = true)] in WCF might keep .NET from getting confused about cyclical references. That's when I get this beauty.
"The type 'KnockoutTest.Models.Person' cannot be serialized to JSON
because its IsReference setting is 'True'. The JSON format does not
support references because there is no standardized format for
representing references. To enable serialization, disable the
IsReference setting on the type or an appropriate parent class of the
type."
This error is very important because it basically tells us that we NOT going to be able to use Upshot AND Entity Framework Code-First together in their normal configuration. Why? Entity Framework is designed to utilize two-way binding. However, when two-way binding is implemented, Upshot says that it cannot handle cyclical references. When cyclical references are managed, Upshot basically says that it cannot handle references between parent and child objects because JSON doesn't support it.
When I watched Steve's demo, I recalled that he DID have a relationship between Customers and Deliveries. I decided to go back and take a much closer look at his object model.
public class Customer
{
public int CustomerId { get; set; }
public string Name { get; set; }
public string Address { get; set; }
}
public class Delivery
{
// Primary key, and one-to-many relation with Customer
public int DeliveryId { get; set; }
public virtual int CustomerId { get; set; }
public virtual Customer Customer { get; set; }
// Properties for this delivery
public string Description { get; set; }
public bool IsDelivered { get; set; } // <-- This is what we're mainly interested in
What we find is that in Steve's demo is that his relationship only goes one way, and it binds the child to the parent rather than the parent to the children.
In this demo, it kind of works. However, in many real-world applications, this approach makes data access impractical. Take, for example, the demo scenario I included in my original question. We have:
Clients
Projects
Persons
Addresses
PhoneNumbers
Most developers, I think would not want to start their query from addresses or phone numbers. They would expect to be able to select a list of clients or Projects or Persons and then navigate to a list of its descendants.
I am not 100% certain that is impossible to use entities which have two-way binding enabled, but I am unaware of any configuration that is likely to yield success using only the Microsoft tools.
Fortunately, I do think there is a solution (which takes care of the cyclic dependency issue) which I plan to test in the next few days. That solution is... JSON.Net.
JSON.Net supports cyclic dependencies and maintains references to child objects. If it works as expected, it will take care of two of the errors I got in my testing.
Once I have tested, I will report results here.
I think Steve's demo was brilliant, and I loved his demo. I believe Knockout is amazing. I am very thankful for where Microsoft seems to be going. If there are noteworthy limitations in the tool, I think Microsoft maybe should have been more forthcoming with them.
I don't mean to be overly critical of Microsoft (and definitely am not critical of Steve at all) because I think they have done a wonderful job. I love what upshot promises and am looking forward to seeing where it goes.
I would really love to see someone take upshot and re-factor it (and the WebAPI) so that it can integrate fully with Entity Framework without the use of a third-party tool.
I don't know if a similar tool exists for NHiberbnate, but I would love to maybe even see someone extend upshot to integrate with (or develop a similar library for) NHibernate. By extend, I am primarily talking about consuming the meta-data from NHibernate.
When I test JSON.Net, I also plan to test NHibernate as well.
If you expose navigation property on both sides of the relation you will get a cycle. For example Client instance contains collection of related Project instances and those Project instances contains navigation property back to their principal Client instance = cycle.
The workaround is either using navigation property only on one side of the relation, using serialization which can resolve cycles out of the box or exclude navigation property on one side from serialization (try to mark it with IgnoreDataMemberAttribute).
I am new to EF. I am trying to get Entity Framework 4.2 to do a sort by a calculated property (not mapped).
Here is what my entity look like:
public class Site : Entity
{
public Site()
{
Equipments = new HashSet<Equipment>();
Forecasts = new HashSet<Forecast>();
}
[StringLength(8)]
public string Number { get; set; }
[StringLength(50)]
public string EquipmentShortCLLI { get; set; }
[StringLength(50)]
public string Location { get; set; }
public virtual Central Central { get; set; }
public virtual ICollection<Equipment> Equipments { get; set; }
public virtual ICollection<Forecast> Forecasts { get; set; }
#region Calculated Items
public bool IsEmbargo {
get { return Equipments.Count > 0 && Equipments.SelectMany(x => x.EquipmentDetails).Any(e => e.IsEmbargo); }
}
//...
public int PortsCapacity
{
get
{
return Equipments.Count > 0
? Equipments.SelectMany(x => x.Slots).Sum(x => x.PortsCapacity)
: 0;
}
}
#endregion
//...
By trying to order using any of my readonly properties I am getting the exception:
The specified type member 'PortsCapacity' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.
Which makes sense because EF is trying to build an sql orderby with a field that does not exist in the database (my understanding..).
Now, by using some dynamic linq code I was able to make this work for my many-to-one columns by passing "Central.SomeField" (as opposed to making a ReadOnly Property that returns Central.SomeField).
I.E.:
query.OrderBy("Central.SomeField");
However, I still face the same issue when it comes to a collection of items (Equipments). I am trying to make this as dynamic as possible by using a string coming from the client side and avoiding a long switch case, but at this point I will accept any ideas, so long as the sorting happens on the database side.
Edit 1:
Following what Ladislav Mrnka says, how would one execute an OrderBy clause on one-to-many child items using lambdas or expression?
I don't think that Dynamic Linq is capable of this. You need a real Linq subquery to compute aggregations on Equipements so it will simply not work. If the user selects ordering by IsEmbargo or PortsCapacity you must have some switch / if block to handle this case by appending special part of the query - no other way.
I'm in the process of writing a BSD licensed mini-ORM targeted at embedded databases (with support for ese, sqlite and sqlce out of the box)
After working lots with Rails in the last year I have been thinking of implementing an Active Record pattern in C#.
I have come up with some demo code and was wondering if the interface design is sound.
Here you go:
// first param is the class, second is the primary key
public class Order : ActiveRecord<Order,int> {
BelongsTo<Customer> Customer { get; set; }
[PrimaryKey(AutoIncrement=true)]
public int Id { get; set; }
public string Details { get; set; }
}
[Index("FirstName", "LastName")]
[Index("LastName", "FirstName")]
public class Customer : ActiveRecord<Customer,int>
{
public HasMany<Order> Orders { get; set; }
[PrimaryKey(AutoIncrement=true)]
public int Id { get; set; }
[ColumnInfo(MinLength=4, MaxLength=255, Nullable=false)]
public string FirstName { get; set; }
[ColumnInfo(MinLength=4, MaxLength=255, Nullable=false)]
public string LastName { get; set; }
public string Comments { get; set; }
}
[TestClass]
public class TestActiveRecord {
public void Demo()
{
var customer = Customer.Build();
customer.FirstName = "bob";
customer.LastName = "doe";
var order = customer.Orders.Build();
order.Details = "This is the first order";
customer.Save();
var customer2 = Customer.Find(customer.Id);
Assert.AreEqual(1, customer2.Orders.Count);
}
}
Sorry about this being a multiple questions in one question ...
Can you think of any changes to this API? Are there any fatal flaws? Are there any open source ORMs that define similar interfaces?
The Castle Active Record Project.
Although it's not a strict implementation of the Active Record pattern, it works very well. Bonus is you will get some experience with NHibernate in the process.
As someone who has written his own, very simple, OR/M only to find it lacking when scenarios got more complex, I would strongly urge you to take a hard look at Caste ActiveRecord and NHibernate, unless you are doing this as a learning experience.
ActiveRecordMediator
Create a repository class that inherits from this AR class. Then you don't break your hierarchy and you implement a repository pattern along with your AR pattern!
Could someone possibly provide code to a very simple activerecord class that I could use to learn with? Looking at the source on projects like Castle and SubSonic is a bit overwhelming. I'd like to learn the active record pattern to get an idea of how it works. I know whatever I build would be nothing compared to Castle or SubSonic, but I think the learning experience would be great.
I looked at Hayden ActiveRecord, but I can't seem to find the source. Most of the active record related postings on his site are quite old.
Thanks.
Edit:
Sorry, I should have created a new question for this...