How can I make such behaviuor in NHibernate:
There is an entity called User in my domain
// I ommit mapping attributes
public class User
{
int Id {get; set;}
int pId {get; set;}
//....other props, such as Login, Name, email...
}
I need to make full copy of it, when updating. pId must be set to original Id. Old entity must be untouched.
So this must be like some versioning system, where pId - is immutable identity, and Id - is like version. I`ve tried to use Version mapping attribute, but it just updates Version field, withou recreating full entity. What approach will be better?
I wrote a versioning system for our application. I split the versioned object into two classes, one that represents the whole object and one for its versions.
In our software, the versioning is part of the business logic. The application provides access to the history and the user has some control over the versioning.
A new version is therefore created in memory. You need to perform a deep-copy. You could implement this by implementing an interface in the root entity and all its children. This interface provides a method DeepCopy which is recursively called through the object graph.
There is also a protected MemberwiseCopy method in object, which could be helpful. It does not a deep copy.
We didn't want the pain to maintain the code which copies each single property. So we are using serialization to copy an object graph in memory:
public static T CopyDataContract<T>(T obj)
{
NetDataContractSerializer serializer = new NetDataContractSerializer();
using (MemoryStream stream = new MemoryStream())
{
serializer.Serialize(stream, obj);
stream.Position = 0;
return (T)serializer.Deserialize(stream);
}
}
Additionally, we have methods in the entities which reset the ids and do some other cleanup. This is also done recursively though the object graph.
For now, it works fine. In the future we probably need to refactor it to the interface implementation, which is a bit cleaner.
Depending on whether history is NOT part of your domain logic I'd suggest using triggers. By not being part of domain logic I mean - you don't need to show it to users, you don't make copies out of historical version.
By using triggers you have several options - the simplest (and implying that you really need to save history only for handful of tables) - would be having a separate _history table that's a copy of your original table.
All in all it really depends on what exactly you are after.
Related
I am developing a website for a beauty salon. There is an admin part of the website, where the esthetician can add a new care. A care is linked to a care category (all cares related to hands, feets, massages, ...). To solve this I wrote this code into the CareRepository in the .NET API :
public async Task<Care?> AddAsync(Care care)
{
// var dbCareCategory = await this._careCategoryRepository.GetByNameAsync(care.CareCategoryName);
if (string.IsNullOrEmpty(care.CareCategoryName) || string.IsNullOrWhiteSpace(care.CareCategoryName))
return null;
var dbCareCategory = await this._instituteDbContext.CareCategories
.Where(careCategory => Equals(careCategory.Name, care.CareCategoryName))
.Include(careCategory => careCategory.Cares)
.FirstOrDefaultAsync();
if (dbCareCategory == null || dbCareCategory.Cares.Contains(care))
return null; // TODO : improve handling
dbCareCategory.Cares.Add(care);
await this._instituteDbContext.SaveChangesAsync();
return care;
}
My problem here is that I am a bit struggling with the best practice to have, because in order to add a care to a category, I have to get the category first. At the first place, I called the CareCategoryRepository to get the care (commented line). But then, EF was not tracking the change, so when I tried to add the care, it was not registered in the database. But once I call the category from the CareRepository, EF tracks the change and saves the Care in the database.
I assume this is because when calling from another repository, it is a different db context that tracks the changes of my entity. Please correct me if my assumption is wrong.
So, I am wondering, what is the best practice in this case ?
Keep doing what I am doing here, there is no issue to be calling the category entities from the care repository.
Change my solution and put the AddCare method into the CareCategoryRepository, because it makes more sense to call the categories entities from the CareCategoryRepository.
Something else ?
This solution works fine, however I feel like it may not be the best way to solve this.
The issue with passing entities around in web applications is that when your controller passes an entity to serve as a model for the view, this goes to the view engine on the server to consume and build the HTML for the view, but what comes back to the controller when a form is posted or an AJAX call is made is not an entity. It is a block of data cast to look like an entity.
A better way to think of it is that your Add method accepts a view model called AddCareViewModel which contains all of the fields and FKs needed to create a new Care entity. Think about the process you would use in that case. You would want to validate that the required fields are present, and that the FKs (CareCategory etc.) are valid, then construct a Care entity with that data. Accepting an "entity" from the client side of the request is trusting the client browser to construct a valid entity without any way to validate it. Never trust anything from the client.
Personally I use the repository pattern to serve as a factory for entities, though this could also be a separate class. I use the Repository since it already has access to everything needed. Factory methods offer a standard way of composing a new entity and ensuring that all required data is provided:
var care = _careRepository.Create(addCareViewModel.CareCategoryId,
/* all other required fields */);
care.OptionalField = addCareViewModel.OptionalField; // copy across optional data.
_context.SaveChanges(); // or ideally committed via a Unit of Work wrapper.
So for instance if a new Care requires a name, a category Id, and several other required fields, the Create method accepts those required fields and validates that they are provided. When it comes to FKs, the repository can load a reference to set the navigation property. (Also ensuring that a valid ID was given at the same time)
I don't recommend using a Generic Repository pattern with EF. (I.e. Repository()) Arguably the only reason to use a Repository pattern at all with EF would be to facilitate unit testing. Your code will be a lot simpler to understand/maintain, and almost certainly perform faster without a Repository. The DbContext already serves all of those needs and as a Unit of Work. When using a Repository to serve as a point of abstraction for enabling unit testing, instead of Generic, or per-entity repositories, I would suggest defining repositories like you would a Controller, with effectively a one-to-one responsibility.
If I have a CareController then I'd have a CareRepository that served all needs of the CareController. (Not just Care entities) The alternative is that the CareController would need several repository references, and each Repository would now potentially serve several controllers meaning it would have several reasons to change. Scoping a repository to serve the needs of a controller gives it only one reason to change. Sure, several repositories would potentially have methods to retrieve the same entity, but only one repository/controller should be typically responsible for creating/updating entities. (Plus repositories can always reference one another if you really want to see something as simple as Read methods implemented only once)
If using multiple repositories, the next thing to check is to ensure that the DbContext instance used is always scoped to the Web Request, and not something like Transient.
For instance if I have a CareRepository with a Create method that calls a CareCategoryRepository to get a CareCategory reference:
public Care Create(string name, int careCategoryId)
{
if (string.IsNullOrEmpty(name)) throw new ArgumentNullException(nameOf(name));
var care = new Care { Name = name };
var careCategory = _careCategoryRepository.GetById(careCategoryId);
care.CareCategory = careCategory;
_context.Cares.Add(care);
}
We would want to ensure that the DbContext reference (_context) in all of our repositories, and our controller/UnitOfWork if the controller is going to signal the commit with SaveChanges, are pointing at the exact same single reference. This applies whether repositories call each other or a controller fetches data from multiple repositories.
It appears that all the existing breezejs examples are passing entity models to and from the BreezeController.
But almost all our pages built are using some form of view models. In the days we have no BreezeJs, we retrieve the data (domain model) from a repository to populate (using AutoMapper or manually) a view model, which contains only the necessary data for that view. The WebAPI sends only the view model data over to the browser where we can populate a client-side view model (usually a knockout observable).
When saving data, we collect data from a <form> to populate an input view model, send only that data over to the server, where data in the input view model is mapped to the domain model. The update is saved by calling SaveChanges() on the DbContext entity in the repository.
Now, BreezeJs is to take over all our repository code by creating an EFContextProvider. The examples I have seen usually retrieve the domain model data and then pass it all to the client side.
[HttpGet]
public IQueryable<Item> Items() {
return _contextProvider.Context.Items;
}
It is the client-side javascript's job to build a view model.
Of course it is possible for us to build the view model at the server side:
[HttpGet]
public List<ItemViewModel> Items() {
var items = _contextProvider.Context.Items
.Include("RelatedEntity")
.ToList();
var model = new List<ItemViewModel>();
.... some code to build model from items ....
return model;
}
The benefit is that less data is transferred across the network, and we can do many manipulations on the server side. But I don't know if it is a good practice to modify this BreezeController like that. But at least, it returns data needed to list all the items.
The real trouble came when I tried to POST data back.
In the BreezeJs examples I found, they use a ko.observableArray() to store all the domain model data, let's say vm.items. Then the new record newItem is build by manager.createEntity into a domain model. After validating the data, item.entityAspect.validateEntity(), the newItem is pushed into vm.items and manager.saveChanges() is called, which somehow invokes SaveChanges() on the BreezeController.
[HttpPost]
public SaveResult SaveChanges(JObject saveBundle) {
return _contextProvider.SaveChanges(saveBundle);
}
I find too many things have been taken over! (Laugh at me if you disagree.) My questions are:
Can I just createEntity and then saveChanges?
I only have an empty form to fill in and submit. There is certainly no need to build a whole items array on the client-side.
Can I pass an input view model as a JObject and do some server-side processing before calling _contextProvider.SaveChanges()?
It turns out to be a super long post again. Thank you for reading it all through. Really appreciate it!
Good questions. Unfortunately, our demo code seems to have obscured the real capabilities of Breeze on both client and server. Breeze is not constrained in the ways that your fear.
I don't want to repeat everything that is in our documentation. We really do talk about these issues. We need more examples to be sure.
You are describing a CQRS design. I think it over-complicates most applications. But it's your prerogative.
If you want to send ItemViewModel instead of Item, you can. If you want that to be treated as an entity on the Breeze client - have the EntityManager turn it into a KO observable and manage it in cache, change track it, validate it -, you'll have to provide metadata for it ... either on server or client. That's true for Breeze ... and every other system you can name (Ember, Backbone, etc). Soon we will make it easier to create metadata on the server for an arbitrary CLR model; that may help.
You have complete control over the query on the server, btw, whether Item or ItemViewModel. You don't have to expose an open-ended query for either. You seem to know that by virtue of your 2nd example query.
On to the Command side.
You wrote: "[the examples] use a ko.observableArray() to store all the domain model data, let's say vm.items"
That is not precisely true. The items array that you see in examples exists for presentation. The items array isn't storing anything from a Breeze perspective. In fact, after a query, the entities returned in the query response (if they are entities) are already in the manager's cache no matter what you do with the query result, whether you put them in an array or throw them away. An array plays no role whatsoever in the manager's tracking of the entities.
You wrote: "Can I just createEntity and then saveChanges?"
Of course! The EntityManager.createEntity method puts a new entity in cache. Again, the reason you see it being pushed into the items array is for presentation to the user. That array has no bearing on what the manager will save.
You wrote: "Can I pass an input view model ... and do some server-side processing before calling _contextProvider.SaveChanges()?"
I don't know what you mean by "an input viewmodel". The Breeze EntityManager tracks entities. If your "input viewmodel" is an entity, the EntityManager will track it. If it has changed and you call saveChanges, the manager will send it to the controller's SaveChanges method.
You own the implementation of the controller's SaveChanges method. You can do anything you want with that JObject which is simply a JSON.NET representation of the change-set data. I think you'll benefit from the work that the ContextProvider does to parse that object into a SaveMap. Read the topic on Customizing the EFContextProvider. Most people feel this provides what they need for validating and manipulating the client change-set data before passing those data onto the data access layer ... whether that is EF or something else.
If instead you want to create your own, custom DTO to POST to your own custom controller method ... go right ahead. Don't call EntityManager.saveChanges though. Call EntityManager.getChanges() and manipulate that change array of entities into your DTO. You'll be doing everything by hand. But you can. Personally, I'd have better things to do.
I have a service object that is responsible for some business logic validation. What it does, before issing Update to repository, is checking whether entity that it works on complies to some business rules.
One of that rules that is must check is if Status property of the entity didn't change when compared to entity that is in database. Because I use repositories that share the same ISession, when I try to get entity from database, in order to get an object for comparsion:
if (fromDbEntity.Status != entity.Status) throw new Exception("Cannot change status...");
I'll always get fromDbEntity that is in 1st level cache - so I work on the same object.
Is there a way to force NHibernate/Repository to get entity from database even though it's already in the scope of the session?
Evict entity from session before loading fromDbEntity
session.Evict(entity);
You can check the official documentation for more details: Managing the caches
The con about this is that you will need to manually call SaveOrUpdate for entity since now the object is out of the session.
You could, as Claudio suggests, evict the entity from the session, then load your fromDbEntity, do the comparison and then Merge the entity again with the session.
Other thing you might do is loading the fromDbEntity using the stateless session instead.
But is this really necessary? Couldn't you just make your Status property read-only? NHibernate is perfectly capable of using fields for accessing data. Or you could make your property setter protected:
public virtual Status Status { get; protected set; }
This way the user won't be able to change the property value, so there's no need to check whether current value is different from db one.
I had a similar issue, I solved it by clearing the session before any call that I want to go all the way to the data base.
session.Clear();
It's a little overkill but it works.
The way you sate your logic, it sounds like there's a potential bug. A much better solution would be to turn on dynamic-update, thus only updating changed values, then validate that no one has changed Status before saving.
So I have a very normalized model, and I'm trying to create a single page application in MVC4 which wants to use an entity framework object. My problem is I can't manage to create an entity in EF with the kind of complex mapping that I need (I have checked multiple guides, but I can't seem to make one entity from multiple tables that contain different primary keys... I found a solution using updateable views, but that's really just pushing the abstraction down to the db layer).
So I thought I could create a POCO object using an EF query to create the object, then on insert/update/delete I could just take the POCO data and update the underlying 3 tables.
Well I hit a roadblock just trying to tweak an existing working controller to try and learn what's going on.
Let's imagine I have a working SPA controller that looks like this:
public partial class FooController : DbDataController<aspnetEntities>
{
public IQueryable<Foos> GetFoos() { ... }
}
I just change it a bit to return my new POCO data object Bar, which let's imagine has the exact same fields as Foo for the moment:
public partial class FooController : DbDataController<aspnetEntities>
{
public IQueryable<Bars> GetBars() { ... }
}
Over in FooViewModel.js I update the operation name to GetBars, and the type from
var entityType = "Foo:#Models";
to
var entityType = "Bar:#Models";
I hit my operation directly and I get:
OLD
<ArrayOfFoo><Foo><Property>true</Property></Foo></ArrayOfFoo>
NEW
<ArrayOfBar><Bar><Property>true</Property></Bar></ArrayOfBar>
So the controller looks like it's giving me what I expect, but when I try to put the whole thing together the SPA flashes up:
You must write an attribute 'type'='object' after writing the attribute with local name '__type'.
I'm guessing somehow I need to get type data into KO? I'm not sure where that might be however, I've been crawling through the JS for hours, but I'm not even clear on where it's failing. Any input would be greatly appreciated.
The problem you are experiencing is connected to the fact you are using POCO instead of the standard EF. It should be related to the webapi serializer that somehow doesn't recognize the class as serializable. Anyway it is a bug that will be removed in the RC. Give a look to this thread for workarounds:
http://forums.asp.net/t/1773173.aspx/1?You+must+write+an+attribute+type+object+after+writing+the+attribute+with+local+name+__type+
In my application I need to save with NHibernate entities received from WCF service.
Currently I'm using session SaveOrUpdate method for this purpose.
Often we don't need to edit reference properties, so from client I receive object, which has empty collections. But I don't want this empty collection to reflect in database.
Example:
public class Product
{
public virtual string Name {get;set;}
public virtual IList<Stores> Stores {get;set;} <--- Stores is empty, but should not be cleared in databse.
}
Thanks,
Oksana.
As far as I understand it, you want to update certain properties of the object if it already exsits, and no touch others, is that correct?
Well, basically, in such a case what you'd need to do is this:
establish an NHiberate session
based on some ID, load the current state of the object from the database
update those properties you want to update from the entity you've received in your service call
save the modified object back
With this approach, you'll only update those properties you want, and everything else is being left alone.
Does that seem like an approach you can work with?
Marc
I'm not sure to understand the question. If you are new to NHibernate have a look at the documentation with the term cascade. This defines what is persisted when an object containing others has to be saved.