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NHibernate - Eager load graphs of objects with multiple queries

I want to cache a never-changing aggregate which would be accessible by a root object only (all other entities are accessible only by using Reference/HasMany properties on the root object)?
Should I use NHibernate (which we are already using) second-level-cache or is it better to build some sort of singleton that provides access to all entities in the aggregate?
I found a blog post about getting everything with MultiQuery but my database does not support it.
The 'old way' to do this would be to
Do a select * from all aggregate tables
Loop the entities and set the References and the Collections manually
Something like:
foreach (var e in Entities)
{
e.Parent = loadedParentEntities.SingleOrDefault(pe => e.ParentId = pe.Id);
}
But surely there is a way to tell NHibernate to do this for me?
Update
Currently I tried merely fetching everything from the db and hope NHibernate does all the reference setting. It does not however :(
var getRoot = Session.Query<RootObject>().ToList();
var getRoot_hasMany = Session.Query<RootObjectCollection>().ToList();
var getRoot_hasMany_ref = Session.Query<RootObjectCollectionReference>().ToList();
var getRoot_hasMany_hasMany = Session.Query<RootObjectCollectionCollection>().ToList();
Domain:
Root objects are getRoot. These have a collection property 'HasMany'. These HasMany have each a reference back to GetRoot, and a reference to another entity (getRoot_hasMany_ref), and a collection of their own (getRoot_hasMany_hasMany). If this doesn't make sense, I'll create an ERD but the actual structure is not really relevant for the question (I think).
This results in 4 queries being executed. (which is good)
However, when accessing properties like getRoot.First().HasMany.First().Ref or getRoot.First().HasMany.First().HasMany().First() it still results in extra queries being executed even altough everything should already be known to the ISession?
So how do I tell NHibernate to perform those 4 queries and then build the graphs without using any proxy properties, ... so that I have access to everything even after the ISession went out of scope?

I think there are several questions in one.
I stopped trying to trick NHibernate too much. I wouldn't access entities from multiple threads, because they are usually not thread safe. At least when using lazy loading. Caching lazy entities is therefore something evil.
I would avoid too many queries by the use of batch size, which is far the cleanest and easiest solution and in most cases "good enough". It's fully transparent to the business logic, which makes it so cool.
I would:
Consider not caching the entity at all. Use NH first level cache (say: always load it using session.Get()). Make use of lazy loading when only a small part of the data is used in a single transaction.
Is there is a proven need to cache the data, consider to turn off lazy loading at all (by making the entities non-lazy and setting all the collections to non lazy. Load the entity once and cache it. Still consider thread safety when accessing the data while it is still loaded.
Should the entities be lazy, because some instances of the same type are not in the cache, consider using a DTO-like structure as cache. Copy all data in a similar class structure which are not entities. This may sound like a lot of additional work, but at the end it will avoid many strange problems and safe you much time.
Usually, query time is less important as flush time. This time is used by NH to find which entities changed in a session. To avoid this, make entities read only if you can.

if the whole object tree never changes (config settings?) then just load them efficiently with all references/collections initialised
using(var Session = Sessionfactory = OpenSession())
{
var root = Session.Query<RootObject>().FetchMany(x => x.Collection).ToFutureValue();
Session.Query<RootObjectCollection>().Fetch(x => x.Ref).FetchMany(x => x.Collection).ToFuture();
// Do something with root.Value
}

entity framework 4: where is my load method and IsLoaded property?

I am using EF4, and I using the System.Data.Entity dll in my class. However, I can't see the load method of my navigation property of my entity.
How can I access to this method?
What I am doing is create e 4.0 project of .NET, create my edmx from a database, right click in the model edmx and I generate a DBContext.
However, I can access to the local property of my context, that I think that is a feature of EF4.
Thanks.
Daimroc.

For the DbContext approach, the IsLoaded property and Load method have been moved:
context.Entry(yourEntity)
.Collection(entity => entity.NavigationProperty)
.IsLoaded;
context.Entry(yourEntity)
.Collection(entity => entity.NavigationProperty)
.Load();
Entry method: http://msdn.microsoft.com/en-us/library/gg696578(v=vs.103).aspx
Collection method: http://msdn.microsoft.com/en-us/library/gg671324(v=vs.103).aspx
IsLoaded property: http://msdn.microsoft.com/en-us/library/gg696146(v=vs.103).aspx
Load method: http://msdn.microsoft.com/en-us/library/gg696220(v=vs.103).aspx

When you write the query (all this also works with lambda syntax as well btw)
From a in context.EntitySet.Include("Navigation Property NAme")
select a
and all will be there ;) .. or more to the point the navigation properties will be populated.
can be wierd with lots of joins though
you can also
From a in context.EntitySet.Include("Navigation1.Navigation2.Navigation2")
.Include("SomeOtherNavigation")
select a
where navigation1 and SomeOtherNavigation are navigation properties on the entity set
Failing that you can turn on lazy loading in the context. But its evil imo.
Also it doesnt really scale well when you go for an SOA approach as you need to include prior to knowing about the lazy load in your repository.
Ie you run the query in your repository, send stuff over the service and then want the navigation properties in the front end ... by which time its too late to lazy load ... EG you are using a wcf service that doesn't use data services.
Important to note that you ahve to use Include on the EntitySet, it is not on an IQueryable<>.
A real example:
var csg = from ucsg in c.UserCarShareGroups.Include("UserCarShareGroups.User.UserVehicles")
where ucsg.User.UserName.ToLower() == userName.ToLower()
&& ucsg.CarShareGroup.Carpark.Name.ToLower().Equals(carparkName.ToLower())
&& ucsg.DeletedBy == null
select ucsg.CarShareGroup;
(the database has case sensitive collation for some reason)
An alternate approach (and maybe more relevant is here)
Entity Framework - Trouble with .Load()
However I like doing it the way I said because it is explicit and I know exactly what is being pulled out. Especially when dealing with large datasets.
An answer to a question that combines my concerns with Load() is here:
Entity Framework 4 load and include combine

How do I make Entity Framework not join tables?

Ok so I am testing out EF once again for performance and I just want a simple result back from my database.
Example
var jobsList = from j in mf.Jobs
where j.UserID == 1001 select new { Job = j };
This unfortunately joins my User object to this list, which I don't want EF to do. How do I tell EF not to join just because there is a relationship. Basically I just want a simple row from that table.
Or do I need to use a different type of retrieval. I am still using the basic type of database retrieval below and I feel there are better ways to handle db work by now.
SqlConnection myconnection = new SqlConnection();
Edit
Basically what I am saying in a more clearer context. Is that instead of only getting the following.
Job.JobID
Job.UserID
//Extra properties
I Get
Job.JobID
Job.UserID
Job.User
//Extra properties
That User object easily consumes way more memory than is needed, plus I don't need it.
My Solution
So I am still not believing in EF too much and here is why. I turned off LazyLoading and turned it on and didn't really notice too much of a performance difference there. I then compared the amount of data that my SqlConnection type method uses compared to my EF method.
I get back the exact same result set and here are the performance differences.
For my Entity Framework method I get back a list of jobs.
MyDataEntities mf = new MyDataEntities(); // 4MB for the connection...really?
mf.ContextOptions.LazyLoadingEnabled = false;
// 9MB for the list below
var test = from j in mf.Jobs
where j.UserID == 1031
select j;
foreach (Job job in test) {
Console.WriteLine(job.JobID);
}
For my SqlConnection method that executes a Stored Proc and returns a result set.
//356 KB for the connection and the EXACT same list.
List<MyCustomDataSource.Jobs> myJobs = MyCustomDataSource.Jobs.GetJobs(1031);
I fully understand that Entity Framework is doing way way more than a standard SqlConnection, but why all this hype if it is going to take at a minimum of 25x more memory for a result set. Just doesn't seem worth it.
My solution is not to go with EF after all.

The User property is part of the job class but wont be loaded until you access it (lazy loading). So it is not actually "joined".
If you only want the two specified columns you can write
var jobsList = from j in mf.Jobs
where j.UserID == 1001
select new {
Job.JobID,
Job.UserID
};

The most probable reason for this behavior is that you have LazyLoadingEnabled property set to true.
If this is the case, the User isn't recovered in the original query. But if you try to acces this property, even if you do it through an inspection while debugging, this will be loaded from the database. But only if you try to access it.
You can check this opening a a SQL Server Profiler, and seeing what commands are begin sent to the DB.
Your code is not using eager loading or explicit loading. So this must be the reason.

I think that EF don't know that you want one result only. Try something like this.
Job jobsItem = mf.Jobs.Single(j=>j.UserID==1001)
If you don't want to use lambas...
Job JobItem = (from j in mf.Jobs where j.UserID == 1001 select j).Single()
I haven't a compiler near right now, I hope the syntax is right. Use can use var instead of Job for your variable if you preffer. It has no effect but I think Job is more readable in this case.

User actually is not attached to context until you access User property of Job. Turn off Lazy Loading if you want to get a null for User.

Entity Framework does not support lazy loading of properties. However, it has table-splitting
Emphasized the properties. Of course, Entity Framework supports lazy loading of rows

WCF Data Services/Entity Framework : Logging client's username, Authentication, Authorization

I am using Entity Framework with WCF Data Services and I have the following table in my database :
Table Contract
Id (int)
Name (varchar)
byUser (varchar)
isDeleted (bit)
Entity Framework class
Id (int)
Name(string)
byUser(string)
isDeleted(boolean)
whenever the user is inserting/updating/deleting a contract(through a client app), I need to log who did the action.
so, I created Stored procedures for insert/update/delete that will receive the username from the client when an insertion/deletion/update is performed.
the issue is that the delete operation does not send over who is performing the operation :
var ctx = Context;
var contractToDelete = ctx.Contracts.Where(c => c.ContractId == 1).First();
contractToDelete.ByUser = username;
ctx.DeleteObject(contractToDelete);
ctx.SaveChanges();
at the server side, the byUser is always null.
Questions :
1) How do I make it so that the byUser parameter is sent to the server ?
2) Is there a better way to handle this kind of scenario ? (logging/authentication/authorization) with Entity Framework

It doesn't send null "always". It sends the old value always. That is some internal logic in entity framework. For each tracked object EF keeps both original and current values. When you are deleting object EF doesn't use current values - it uses original values (don't ask me why, simply this is how it works).
So you need to cheat EF:
var ctx = Context;
var contractToDelete = ctx.Contracts.Where(c => c.ContractId == 1).First();
contractToDelete.ByUser = username;
ctx.Contracts.ApplyOriginalValues(contractToDelete);
ctx.DeleteObject(contractToDelete);
ctx.SaveChanges();
Calling ApplyOriginalValues will force EF to override original values with values passed in parameter = you will override original values with current values.
In my opinion the better way is storing deleted records in separate table because it will avoid a lot of problems with passing isDeleted=false to every query where both eager and lazy loading will load deleted records as well. The only way to avoid problems with isDeleted is using conditional mapping but in such case you will not be able to load deleted records even if you want to unless you use stored procedures or direct SQL queries.

The way I managed this is, when my user logs in, I store basic information about them in the session. I then have a class that sits on top of my actions to context.
Whenever I commit back changes, I go through the same routine which checks what changed. I developed the ability to trigger actions based upon the entity being worked with (so I can keep an eye on something such as contracts). Then I have the user able to be logged.
[Edit]
This is tougher to clarify than I realised, but I'll try.
I'm creating a web application. Heavily using Ninject.
When the user logs in, I store their information in an IUserSession object (this is really held in Session, but a custom Ninject scope makes this neat for me and prevents me from having to expose my data layer to Web Session). This user session object contains username, user id etc.
I created a class that contains the context,and wraps all the SELECT,CREATE,DELETE and COMMIT calls. i.e. SELECT;
public IQueryable<TEntity> All<TEntity>( ) {
return Context.Set<TEntity>();
}
This class also has a Commit method, this is the call to SaveChanges.
Before calling SaveChanges, you have access to the changes in the form of Context.ChangeTracker.Entities
For each entity that has changed, you can test to see if it was added, deleted or modified.To get the type of the element being modified;
Type baseEntityType = ObjectContext.GetObjectType( entity.Entity.GetType( ) );
I do plan on writing up a tutorial soon, based upon my personal experience with doing this (not that that helps you right now).

Reading several tables from one single Entity Framework ExecuteStoreQuery request.

I have a library which uses EF4 for accessing a SQL Server data store. For different reasons, I have to use SQL Server specific syntax to read data from the store (for free text search), so I have to create the SQL code by hand and send it through the ExecuteStoreQuery method.
This works fine, except that the query uses joins to request several tables aside the main one (the main one being the one I specify as the target entity set when calling ExecuteStoreQuery), and EF never fills up the main entity's relationship properties with the other table's data.
Is there anything special to do to fill up these relationships? Using other EF methods or using special table names in the query or something?
Thanks for your help.

Executing direct SQL follows very simple rule: It uses column from the result set to fill the property with the same name in materialized entity. I think I read somewhere that this works only with the the main entity you materialize (entity type defined in ExecuteStoreQuery = no relations) but I can't find it now. I did several tests and it really doesn't populate any relation.

Ok so I'll write here what I ended up doing, which does not looks like a perfect solution, but it does not seem that there is any perfect solution in this case.
As Ladislav pointed out, the ExecuteStoreQuery (as well as the other "custom query" method, Translate) only maps the column of the entity you specify, leaving all the other columns aside. Therefore I had to load the dependencies separately, like this :
// Execute
IEnumerable<MainEntity> result = context.ExecuteStoreQuery<MainEntity>(strQuery, "MainEntities", MergeOption.AppendOnly, someParams).ToArray();
// Load relations, first method
foreach (MainEntity e in result)
{
if (!e.Relation1Reference.IsLoaded)
e.Relation1Reference.Load();
if (!e.Relation2Reference.IsLoaded)
e.Relation2Reference.Load();
// ...
}
// Load relations, second method
// The main entity contains a navigation property pointing
// to a record in the OtherEntity entity
foreach(OtherEntity e in context.OtherEntities)
context.OtherEntities.Attach(e);
There. I think these two techniques have to be chosen depending on the number and size of generated requests. The first technique will generate a one-record request for every required side record, but no unnessecary record will be loaded. The second technique uses less requests (one per table) but retrieves all the records so it uses more memory.