I have two NHibernate-managed entities that have a bi-directional one-to-many relationship:
public class Storage
{
public virtual string Name { get; set; }
public virtual IList<Box> Boxes { get; set; }
}
public class Box
{
public virtual string Box { get; set; }
[DoNotSerialize] public virtual Storage ParentStorage { get; set; }
}
A Storage can contain many Boxes, and a Box always belongs in a Storage. I want to edit a Box's name, so I send it to the client using JSON. Note that I don't serialize ParentStorage because I'm not changing which storage it's in.
The client edits the name and sends the Box back as JSON. The server deserializes it back into a Box entity.
Problem is, the ParentStorage property is null. When I try to save the Box to the database, it updates the name, but also removes the relationship to the Storage.
How do I properly serialize and deserialize an entity like a Box, while keeping the JSON data size to a minimum?
I would recommend you send a DTO to the client for display purposes (and it should contain the unique database ID). Then send the boxId + the new name back up to the server from the client (there is no need to send the entire DTO back). The server can do a database lookup using the ID to get the box object, update the name field to the one sent from the client, and save the box to the database.
There is no need in this scenario to serialize an NHibernate object, that just adds a lot of complexity and no value.
I would guess that ParentStorage is null because it is being lazily loaded. Either configuring it to be fetched eagerly or forcing a read by calling the getter before serialization may help make sure the Storage is serialized, and depending on your ID scheme this may work (I don't know for sure).
The gains from serialization in this case seem minimal, and may have unexpected consequences as the Box and Storage classes evolve. It seems simpler to send up a single string for the name, load the Box, set the string, and save that object. Then you don't have to worry as much about the optimizations Hibernate does underneath.
Related
We have an entity named Organization that we use the UniqueConstraints-bundle on. We have a property named NetName that is a UniqueConstraint and an automaticly generated Id.
Since this is unneccesary we want to use the NetName-property as Id instead. So that we don't need UniqueConstraints to know that it is unique and also get the benefit from being able to use Load when we have the NetName.
We needed to clean up our netname a bit before using it as an Id so we created a new temporary-property called TempUniqueNetName that now holds the value of:
"organizations/"+ CleanupId(this.NetName)
So we are now ready to simply move that value to our Id. But we can't get it to work. Our problem is that with the PatchRequest below we end up with a new property named Id in the database but the acctual Id still has the same value (see screenshot). Is there a better (correct) way to change the value of an Id?
The Entity:
class Organization {
public string Id { get; set; }
[UniqueConstraint]
public string NetName { get; set; }
public string TempUniqueNetName{ get; set; }
}
We want to do something like this:
_documentStore.DatabaseCommands.UpdateByIndex(typeof(Organizations).Name,
new IndexQuery(),
new[]
{
new PatchRequest()
{
Type = PatchCommandType.Rename,
Name = "TempUniqueNetName",
Value = new RavenJValue("Id")
}
});
I don't think you can change the document key via patching. It's not actually stored with the document or the metadata - it's copied into the #id metadata on load to give you the illusion that it's there, and the Raven Client copies it again into your own identity property in the document. But really, it's a separate value in the underlying esent document store. Raven would have to know specifically how to handle this and fake it for you.
You could manually copy the doc from the old id to the new one and delete the old, but that could be time consuming.
There isn't a great answer for renaming a document key right now. There really should be a DatabaseCommand for rekeying a single document, and separate PatchCommandType to rekey when patching. Perhaps this will be added to raven in the future.
You can check implemtation of PUT-DELETE usage for updating IDs in my github repo.
It should look something like this:
store.DatabaseCommands.Put(updatedKey, null, document.DataAsJson, newMetadata);
store.DatabaseCommands.Delete(oldKey, null);
https://github.com/Sevsoad/SagaUpdater/
Also here is some Raven documentation:
https://ravendb.net/docs/article-page/3.0/csharp/client-api/commands/documents/put
With Repository pattern and ViewModels, how do you build queries against the database if you don't want the raw database objects to leak outside the repository? How do I actually create queries without loading ALL the database in memory and using LINQ to Objects? I can't expose IQueryable to the rest of the app.
For example, with EF I have a bunch of POCOs with several properties that match db fields, but also some stuff to work around enums not being directly support (for now) as well as foreign key IDs to prevent N+1 and easier querying and so on. I don't want them to leak out to the rest of the application, I want the application to just see a normal object graph.
public class DbUser
{
public int Id { get; set; }
public string Name { get set; }
public int GroupId { get; set; }
public DbGroup Group { get; set; }
public ICollection<DbComment> { get; set; }
}
public class User
{
public int Id { get; set; }
public string Name { get set; }
public Group Group { get; set; }
public ICollection<Comment> { get; set; }
}
The problem here is my repository will internally use EF for the querying (and in-memory stuff when unit testing). But how do I implement IQueryable<User> FindAll()? I can't just do return dbContext.Users.Select(u => new User(u)), as in that case I lose all possible query ability; it'll just load the whole user collection in memory, convert all the types to User from DbUser and then build LINQ queries on the in-memory collection - that is horribly inefficient.
I can't just build queries in the repository. On some pages I have queries that select a few fields, but also calculate some complex stuff from other related objects, filter them based on the result (for example count of comments with positive score), but I also need that back in the application. I could select all objects used to get the complex stuff and return them to the application (but not as db entities) but that would mean select a LOT of data.
Basically how do I prevent the database entities from polluting the rest of the application with their cruft and hacks, while still maintaining the ability to build queries outside of the repository?
CQRS (Command Query Responsibility Segregation) solves this problem. You have the 'real' model , the Domain model, with all the business rules and all that, and a 'query-ony' model which basically is a simple poco (which can be used directly by Views) that will be returned by a specialised query only repository.
The peristence model (EF entities) are used only to 'talk' with the db, the repos always returns or deals with domain/ application objects. Basically, you have to map the EF entities to the Domain ones (and viceversa when saving). In this way, you'll have separated models each with its own purpose.
I have a domain model that includes something like this:
public class Customer : EntityBase<Customer>, IAggregateRoot
{
public IList<Comment> Comments { get; set; }
}
public class Comment : EntityBase<Comment>
{
public User CreatedBy { get; set; }
public bool Private { get; set; }
}
I have a service layer through which I retrieve these entities, and among the arguments passed to that service layer is who the requesting user is.
What I'd like to do is be able to construct a DetachedCriteria in the service layer that would limit the Comment items returned for a given customer so the user isn't shown any comments that don't belong to them and are marked private.
I tried doing something like this:
criteria.CreateCriteria("Comments")
.Add(Restrictions.Or(Restrictions.Eq("Private", false),
Restrictions.And(Restrictions.Eq("Private", true),
Restrictions.Eq("CreatedBy.Id", requestingUser.Id))));
But this doesn't flow through to the lazy-loaded comments.
I'd prefer not to use a filter because that would require either interacting with the session (which isn't currently exposed to the service layer) or forcing my repository to know about user context (which seems like too much logic in what should be a dumb layer). The filter is a dirty solution for other reasons, too -- the logic that determines what is visible and what isn't is more detailed than just a private flag.
I don't want to use LINQ in the service layer to filter the collection because doing so would blow the whole lazy loading benefit in a really bad way. Lists of customers where the comments aren't relevant would cause a storm of database calls that would be very slow. I'd rather not use LINQ in my presentation layer (an MVC app) because it seems like the wrong place for it.
Any ideas whether this is possible using the DetachedCriteria? Any other ways to accomplish this?
Having the entity itself expose a different set of values for a collection property based on some external value does not seem correct to me.
This would be better handled, either as a call to your repository service directly, or via the entity itself, by creating a method to do this specifically.
To fit in best with your current model though, I would have the call that you currently make to get the the entities return a viewmodel rather than just the entities;
public class PostForUser
{
public Post Post {get; set;}
public User User {get; set;}
public IList<Comment> Comments}
}
And then in your service method (I am making some guesses here)
public PostForUser GetPost(int postId, User requestingUser){
...
}
You would then create and populate the PostForUser view model in the most efficient way, perhaps by the detached criteria, or by a single query and a DistinctRootEntity Transformer (you can leave the actual comments property to lazy load, as you probably won't use it)
Here's the scenario:
I've got an association between "Groups" and "Users, represented by a "UserGroupAssignment" object.
public class UserGroupAssignment
{
[Key]
public virtual long Id { get; set; }
[Association("UserAssignmentToUser", "UserId", "Id", IsForeignKey = true)]
public virtual User { get; set; }
[Association("UserAssignmentToGroup", "GroupId", "Id", IsForeignKey = true)]
public virtual Group { get; set; }
public virtual bool IsPrimary { get; set; }
public virtual DateTime? ValidFrom { get; set; }
public virtual DateTime? ValidTo { get; set; }
}
I have two business logic methods, GetUserAssignmentsForGroups and GetGroupAssignmentsForUsers that I return the assignments with the User and Group properties populated respectively. i.e. GetUserAssignmentsForGroup takes a GroupId and returns the assignments for that Group with the User property populated.
What I want is to expose those two methods as domain query methods like so:
[Query]
public IQueryable<UserGroupAssignment> GetAssignmentsForGroupWithUsers(long groupId)
{
return this.businessLogic.GetUserAssignmentsForGroups(groupId);
}
[Query]
public IQueryable<UserGroupAssignment> GetAssignmentsForUserWithGroups(long userId)
{
return this.businessLogic.GetGroupAssignmentsForUsers(userId)
}
My problem is that whilst the business logic methods return the correctly populated Assignments via NHibernate, RIA Services is NOT passing the sub-entities (User or Group) across the wire.
I don't want to use [Include] attributes on the User or Group properties of the UserAssignment class, as I want to minimise the payload over the wire - I don't want to send the group over when I'm only interested in the User of each UserAssignment, for example.
So my question is this:
How do I tell RIA services to
explicitly include User sub-entities
in one domain query method and Group
sub-entities in the other?
Remember, I'm using NHibernate at the back end and custom query methods in the RIA Services, so can't use the EF-style include in the client query.
Thanks
Joel
you should apply the [Include] attribute in the metadata class. then create one domain service method for fetching data without properties included, and a separate method for fetching data with properties included.
You might find this thread helpful in understanding how [Include] attribute works.
Old question, but still interesting. Did you find a solution ?
As far as I know of WCF RIA Architecture it isn't so easy.
An easy and dirty way could be to override the Query method, force the enumeration of the IQueryable being returned (I guess you're using LINQ to nHibernate, in which case, good luck) then examine the HttpContext (you're using WCF RiaServices so you MUST have aspNetCompatibility turned on) and set to null the reference that you don't want to send over the wire (User or Group).
Anyway this way FORCE you to use the [IncludeAttribute]. However I don't see any reasonable route that avoid its use, and this way allow you to send the entity over the wire just when you need to.
IMO I belive that in order to totally avoid the use of [Include] you must rollout your own serializer serverside and deserializer clientside or change the UserGroupAssignment entity so that the user property become a string containing the serialized User (or Group) that you decide to valorize or not according your method.
Please let us knows if you already found a solution, the question is interesting.
I'm still learning here and have a question about child collections. I have an aggregate root called Audio, which has a collection of AudioDownloads.
The downloads are records of each IP address which downloads the audio, i don't want to have duplicate records of the same IP for each Audio.
In my domain i have the following function:
public virtual void Add(AudioDownload download)
{
if (!AudioDownloads.Contains(download)) {
TotalDownloads++;
AudioDownloads.Add(download);
}
}
And this is how i am calling the Add function:
var download = new AudioDownload();
audio.Add(download);
This is returning all downloads from the database for this Audio (which chould be thousands!), also it's still adding the download even though one already exists.
I'm using S#arp with the DomainSignature approach for comparing my entities.
Here is my Domain:
public class AudioDownload : Entity, ITenantSpecific
{
public AudioDownload() { DateAdded = DateTime.Now; }
[DomainSignature]
public virtual Audio Audio { get; set; }
[DomainSignature]
public virtual string Ip { get; set; }
public virtual DateTime DateAdded { get; set; }
}
My question is...even if i can get AudioDownloads not to add duplicate entries, should i be doing it this way at all?
Thank you very much!
Paul
I expect that most ways to do this will always lead you to query all downloads from the database, which is probably not what you want.
Another approach that might be cheaper is just to have a unique key in the database defined based on AudioId and Ip. If you then insert a record that duplicates these you will get an exception from NHibernate telling you a unique key was violated: handle that exception gracefully (i.e. don't show it as an error, load the existing AudioDownload and use that in future) and you will have achieved your goal, I believe.
When you use this approach do not check whether the download is already contained in the collection, since that would still trigger loading of all records.
On the other hand: would it not be interesting to see that something was downloaded from the same Ip multiple times?