I'm using S#arpArchitecture (ASP.NET MVC and Fluent NHibernate). I have an entity as follows:
public class User : Entity
{
public User(){}
public User(string firstName, string lastName)
{
FirstName = firstName;
LastName = lastName;
}
public virtual string FirstName { get; set; }
public virtual string LastName { get; set; }
public virtual DateTime? LastUpdate{ get; set; }
}
I will call the SaveOrUpdate method on my repository class that will persist this User object. It works. How would i persist the LastUpdate property automatically with the latest date and time? I could override the SaveOrUpdate method in my repository by always setting the LastUpdate property to the current date and time but that does not seem to be correct because if there's nothing changed in my entity, I don't think NHibernate will persist my object back to the DB and forcing the setting of this property will always make it persist back.
I only want this LastUpdate property set if something else has changed in my entity.
You should use an NHibernate Interceptor to accomplish this. Override OnFlushDirty in your interceptor implementation to set the LastUpdate property only when something has changed (i.e. your object is dirty).
Since you didn't specify your database type, I will take the liberty and add a solution for people using MySQL / MariaDB:
You can use the following in your fluent mapping class:
Map(y => y.LastUpdate).CustomSqlType("timestamp").Generated.Always();
This creates a MySQL TIMESTAMP column with a default value of CURRENT_TIMESTAMP. Thus, if Nhibernate chooses to flush your entity, MySQL will make sure that the column is properly updated.
I'm pretty sure this does not play well with MSSQL as TIMESTAMPS are different beasts in MSSQL (here and here)
I'm going to point to another StackOverflow question that I think answers my question.
Related
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.
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 am working on an NHibernate project and have a question regarding updating transient entities.
Basically the workflow is as follows:
Create a DTO (projection) and send over the wire to client. This has a small subset of properties from the entity.
Client sends back the changed DTO
Map the DTO properties back onto the appropriate enitity so an UPDATE statement can be generated and executed by NH.
Save the entity
Point 4 is where I have the issue. Currently I can achieve this update using the session.Merge() method, however it must first load the entity from the db (assume no 2LC) before updating. So, both a select and an update statement are fired.
What I would like to do is create a transient instance of the entity, map the new values from the DTO, then have NH generate a SQL statement using only the properties I have changed. The additional select should be unnecessary as I already have the entity ID and the values required for the SET clause. Is this possible in NH?
Currently using session.Update(), all properties will be included in the update statement and an exception is raised due to the uninitialized properties that are not part of the DTO.
Essentially I need a way to specify which entity properties are dirty so only these are included in the update.
== EDIT ==
For example...
public class Person
{
public virtual int PersonId { get; set; }
public virtual string Firstname { get; set; }
public virtual string Nickname { get; set; }
public virtual string Surname { get; set; }
public virtual DateTime BirthDate { get; set; }
}
And the test case.
// Create the transient entity
Person p = new Person()
p.id = 1;
using (ISession session = factory.OpenSession())
{
session.Update(p);
// Update the entity – now attached to session
p.Firstname = “Bob”;
session.Flush();
}
I was hoping to generate a SQL statement similar to ‘UPDATE Persons SET Firstname = ‘Bob’ WHERE PersonID = 1’. Instead I get a DateTime out of range exception due to BirthDate not being initialised. It shouldn’t need BirthDate as it is not required for the SQL statement. Maybe this isn’t possible?
== /EDIT ==
Thanks in advance,
John
Dynamic-update is what you're looking for. In your mapping file (hbm.xml):
<class name="Foo" dynamic-update="true">
<!-- remainder of your class map -->
Be aware of the potential problems that this may cause. Let's say you have some domain logic that says either FirstName or Nickname must not be null. (Completely making this up.) Two people update Jon "Jonboy" Jonson at the same time. One removes his FirstName. Because dynamic-update is true, the update statement just nulls out Jon and the record is now "Jonboy" Jonson. The other simultaneous update removes his Nickname. The intent is Jon Jonboy. But only the null-out of the Nickname gets sent to the database. You now have a record with no FirstName or Nickname. If dynamic-update had been false, the second update would have set it to Jon Jonboy. Maybe this isn't an issue in your situation, but setting dynamic-update="true" has consequences and you should think through the implications.
UPDATE: Thanks for the code. That helped. The basic problem is NHibernate not having enough information. When you say session.Update(p), NHibernate has to associated a disconnected entity with the current session. It has a non-default PK. So NHibernate knows that it's an update and not an insert. When you say session.Update(p), NHibernate sees the whole entity as dirty and sends it to the database. (If you use session.Merge(obj), NHibernate selects the entity from the database and merges obj with it.) This is not what you really mean. You want to associate your object with the current session, but mark it as clean. The API is somewhat non-intuitive. You use session.Lock(obj, LockMode.None) as below.
using(var session = sessionFactory.OpenSession())
using(var tx = session.BeginTransaction()) {
var p = new Person {PersonId = 1};
session.Lock(p, LockMode.None); // <-- This is the secret sauce!
p.Firstname = "Bob";
// No need to call session.Update(p) since p is already associated with the session.
tx.Commit();
}
(N.B. dynamic-update="true" is specified in my mapping.)
This results in the following SQL:
UPDATE Person
SET Firstname = 'Bob' /* #p0_0 */
WHERE PersonId = 1 /* #p1_0 */
I'm a new NHibernate developer. I'm using attributes and not map files and I have configured the application to create the tables automatically.
I Have two classes , Group and User.
Withing the Group class I have a list of users
public class Group
{
[NHibernate.Mapping.Attributes.Id(Name = "GroupId")]
[NHibernate.Mapping.Attributes.Generator(Class = "guid")]
public virtual Guid GroupId { get; set; }
// What Attributes do I place here
public virtual List<User> Users { get; set; }
}
I can't find the right attributes so that there will be two tables that have one to many relation.
Can anyone help?
Thanks,
Ronny
[ManyToMany], [OneToMany] or [ManyToOne] (those linked docs are fairly useless though) depending on how you want it setup. Probably [OneToMany], and then the same on a User.
You could avoid the pain by using the Fluent NHibernate library instead, if you haven't already tried it.
Using NHibernate, what is the best way to handle InsertDate (a.k.a CreateDate) and UpdateDate columns?
For example:
public class Customer
{
public virtual string Name { get; set; }
public virtual DateTime InsertDate { get; set; }
public virtual DateTime UpdateDate { get; set; }
}
There are probably multiple ways that this could be handle, but could someone who has done this before provide me with some advice.
If it's not obvious, I want InsertDate to be set to the date that a record was inserted and after that to be immutable. UpdateDate needs to be changed every time a record is updated.
Bonus marks if you answer using Fluent Nhibernate.
Use auditing interceptors for this. A good example can be found here.
I've used something similar to Ayende Rahien.
Not so important - just to be complete - my version used Interceptors, not listeners. For more infos to interceptors and listeners read this stackoverflow question.