As an FNH user, do you find you sometimes need to supplement FNH with an hbm file? Any relatively common edge cases where you do, if so?
Cheers,
Berryl
If you need to use named queries you will need to use an hbm file and you would probably use a named query to call a stored procedure whether this be because you have legacy stored procs to call, possibly performance or in my most recent case, to do a full text search. More info on setting this up can be found here and here.
When a bug in Fluent NHibernate prohibits something. There are less bugs each release, but you might find some eventually (the most recent is the inability to map dictionaries when certain auto mapping conventions exist)
When you have a legacy system (mapped using hbms) for which you need to add new domain objects (mapped using fnh and/or automapping).
I'm using FNH Automapping on my (so far, one and only) NHibernate project.
At first, I had to write a couple of FNH overrides to work around bugs. But the bugs were quickly fixed by the FNH team, and I was able to eliminate the overrides completely.
Never had to deal with the HBM files, and I hope it stays that way!
Related
I have several projects using NH and FNH to generate the mappings (some Fluent some Automapped). There are still some bugs and missing features i need, but it seems that FNH could die because of mapping-by-code integrated into NHibernate.
Question: Contribute to FNH or to migrate the mappings to mapping-by-code or confORM and fixing problems/implementing features there?
At our office, we have been using NHibernate for 3 years now. We've been thinking about making a move to Fluent Nhibernate but never made the move. Using hbm.xml files was still the easiest to debug/alter. Two common problems of those xml files are that they are all validated during the creating of the sessionfactory and they are not refactor-safe.
Due to a bug I had to update a newer release of NHibernate (we were using NHib 2.1.2GA) and when I implemented 3.2GA we also were handed the ability to use loquacious mappings (mapping by code). I decided to use Loquacious over Fluent because I don't have a dependency to another project (Fluent) and the fact that NHibernate won't be shipped if mapping by code is broken.
Be aware though, that Loquacious mapping isn't complete either. While I was mapping everything by code, I found out basic stuff like property-ref wasn't always implemented. Thus even though it's shipped, it's not 100% complete. And while this will not come as a shocker, it has bugs. yes. really. ;-)
for more info on (reported) bugs, check out the NHibernate bug database: https://nhibernate.jira.com/browse/NH
Hope this helps.
Regards, Ted
thx to #TedOnTheNet i will continue to use and contribute to FNH, because it will take a while until mapping-by-code reaches FNH in some areas
Automapping
Fluent API tells a lot better which possibilities there are
far more verbose mappings
.Database(SQLiteConfiguration.Standard.InMemory()) is still easier to figure out than
.DataBaseIntegration(db =>
{
db.ConnectionString = ???;
db.Dialect<SQLiteDialect>();
db.Driver<???>();
});
and some features:
CompositeId and Table per Subclass
default values for legacy columns
property refs
Update: some features from hbm.xml (and FluentMapping) will not be possible at all with mapping by code:
default values for legacy columns: database column to constant value without the need for a property in the entity class with mapping by code
query only properties/collections: http://ayende.com/blog/4054/nhibernate-query-only-properties
NH 3.2 does not have anything remotely equivalent to FNH's Automapping, as far as I can tell. (For me, that would be a dealbreaker).
Edit
The FNH Automapper can deal with most of the common patterns in an object model, such as inheritance, one-to-many relationships, self-referencing, etc - without requiring any help from the programmer. So far, pure NH has not achieved this level of automation.
Also, James Gregory has publicly stated that he will continue to develop FNH, at least in the near term. (Think I saw this on the FNH Google group a few months back, but I'm not sure exactly where).
I'm trying to get into using Fluent NHibernate, and I have a couple questions. I'm finding the documentation to be lacking.
I understand that Fluent NHibernate / NHibernate allows you to auto-generate a database schema. Do people usually only do this for Test/Dev databases? Or is that OK to do for a production database? If it's ok for production, how do you make sure that you're not blowing away production data every time you run your app?
Once the database schema is already created, and you have production data, when new tables/columns/etc. need to be added to the Test and/or Production database, do people allow NHibernate to do this, or should this be done manually?
Is there any REALLY GOOD documentation on Fluent NHibernate? (Please don't point me to the wiki because in following along with the "Your first project" code building it myself, I was getting run-time errors because they forget to tell you to add a reference. Not cool.)
Thanks,
Andy
I've been using Fluent NHibernate Automapping for a few months now. I'm by no means an expert, but can take a stab at your questions...
FNH Automapping does indeed create DB schemas from POCO classes, including lists of other objects (this was the reason I chose NHibernate in the first place).
When you change schemas, you have to rerun the automapping, which does drop the whole database, unfortunately. In my case, it's not a big problem because I'm importing existing binary data files, so I just have to re-import my data every time the schema changes. I've read that there's some data migration support available with NHibernate, but have no experience with this. (BTW, Subsonic will do data migration, but it's automapping functionality is far more rudimentary - at least it was when I evaluated it a few months ago)
FNH documentation is one of my pet peeves - they have not even added Intellisense help on the method names, etc. (But they get really huffy when you point that out - ask me how I know!) I've made a couple of edits to the wiki when I could, but there's so much more that could be done there. The best approach is to start with a working example (i.e.
this one from Nikola Malovic, and post questions to the support form if (when!) you run into trouble. In general, I've found the FNH community pretty helpful, and have been able to work through all my difficulties. They've also fixed a couple of bugs I've found.
Overall, using FNH has been a huge win for my project - highly recommended!
I don't use Fluent, but I can help with classic NHibernate.
yes, the creation of the schema is very recommendable for production use (Schema Export). When you do this is up to you. For instance, you could create the database by an installer. You shouldn't drop existing databases, but this is a decision of you application.
I don't understand this question. Do you mean you need to upgrade an existing database to a new database schema? This is unfortunately something you need to implement yourself. NH can't do much about this, because it is very specific to you data and the changes you made. There is also a Schema Update or something like this, which is not recommended for production use.
I don't use Fluent, so I can't help here.
I am trying to integrate NHibernate into an existing application with several hundred tables. Due to the fact that there apparently wasn't a strict adherence to conventions, I am unable to use Automap. As a result, I'm going to use Fluent to manually map over all of the associations.
Rather than doing it by hand, I'm hoping that there is a tool in existance that can either run through my solution or the database and stub out mappings.
Does anyone know of any project out there with this in mind?
Thanks!
I don't know of a tool that does it in Fluent, but there are plenty of options for doing it with the old hbm xml files. CodeSmith and MyGeneration are two that are recommended as a starting point for your classes and hbms.
LLBLGen Pro V3 will do exactly this, it can generate either tradition .hbm.xml or fluent mappings for your entire database.
Old question, maybe still relevant to some. If you are looking for an open source solution, try NHibernate Mapping Generator
One thing that bothers me about nHibernate is that it is not 100% compile time tested.
If I rename a column in my database table, and I update the mapping file for that table, when I hit compile I should get errors in all my query code (hql/criteria whatever) of where I referenced that column name and how it is spelled wrong.
The whole point (for me anyway) of using an ORM was that database changes won't break my queries.
In other words, I will be notified at compile time of what needs to be fixed, instead of getting runtime errors etc.
To achieve what you want I think your best solution is to use a combination of Fluent NHibernate and nhlambdaextensions. Fluent NHibernate will give you type-safe checking on your mapping files (so if you change a property on your entity, the compiler will throw an error if you don't also change the property on your mapping class). The lambda function extensions will give you type-safe queries via the Criteria API (not HQL since that's just magic-strings SQL-with-objects).
Also to clarify your question, you said:
If I change a column (rename) in my
database table, and I update the
mapping file for that table, when I
hit compile I should get errors in all
my query code (hql/criteria whatever)
of where I referenced that column name
and how it is spelled wrong.
Just changing the database side should break nothing (assuming you also make the change in your XML mapping file). Your code does not reference the column="first_name" portion of the mapping, it references the name="FirstName" portion. If you do not change your entity, renaming a column (from "firstname" to "first_name", for example) in the database will not break your queries as long as you update your mapping file as well.
You should look at Castle ActiveRecord. I used this before and it allows you to not worry about the mapping files (.hml) as much. It lets you make your changes at the class level definitions, and the mappings files were generally untouched.
If you are writing bad queries, that sounds like a design problem, not an nHibernate problem.
You won't get errors providing the Property names haven't changed, as most people use HQL for their queries in NHibernate.However if you do change the Property names and not the HQL you will indeed get broken queries, e.g.:
FROM User Where User.Surname = 'bob'
Change the Surname property to Lastname and it'll break. It's a feature lacking in NHibernate but would make a good project for the contrib - a Subsonic style query interface. This a project sort of similar but still use HQL.
As mentioned above ActiveRecord and Fluent NHibernate are the closest to type checking with NHibernate. Both enforce that you inherit your classes from their base class, as you'd expect and ActiveRecord is not intended for production use - Ayende has said in a video that's meant to be a prototyping tool for NHibernate.
Hibernate uses dynamic byte code generation to create the mapping classes, based on the mapping configurations.
The fundamental point of ORM is to enable auto-magical mapping (bridge) between Objects and Relational systems. Thus: ORM.
if you want to strongly type your objects rather than using xml config which can cause alot of runtime issues if not properly tested, I would look into FluentNHibernate which has convention maps that allow you to map your classes to data in code. Made my life alot easier especially when first starting with NHibernate wish i had found it before i knew how to properly map using xml
Does NHibernate have the equivalent of the Java version's schema validator? In which case, you could add a step to your build process to build the session factory and run the validator-- building the session factory should also compile named queries, hence validating them too.
Hmm, looks like it supports something like that: http://nhibernate.info/blog/2008/11/22/nhibernate-schemavalidator.html
NB this means your build process will fail to work if your dev database is not available--- which I would regard as a bad thing.
I am in a stage of mapping my CSharp classes into database tables. I have decided to use NHibernate as my ORM tool after comparing with other tools. I have never done a real project with NHibernate before and now am considering alternatives for the mapping,
ActiveRecord: according to the project's web site, using ActiveRecord can boost productivity dramatically. However, I do not like the idea of adding attributes to my CSharp classes. After all, my class should NOT have any knowledge of database relationships. By using ActiveRecord will bind my nicely separated classes to ActiveRecord, and give me hard time if I ever want to switch underline DAO Layer implementation in the future.
FluentNHibernate: FluentNhibernate was my first attempt when starting mapping. But I also have a few issues with this approach. 1) I don't like my mapping strategies compiled as binary files. I would like to be able to change mapping by modifying xml files. 2) The maturity of FluentNHibernate. NHibernate has been around for a long time, and has LOTS of users, so I am quite comfortable with its maturity. On the contrast, FluentNhibernate is relatively young and not been tested by as many users. Even though I could dive into the source to fix whatever issue comes up, I am not comfortable with my skills to touch the low level implementation. 3) Availability of documentation for FluentNHibernate is much than that of NHibernate. I would like to have a place to go when I hit a hard wall.
NHibernate: Currently, I am using naked Nhibernate xml to do the mapping. To be honest, working with XML gives me massive headaches. Literally, I have to keep myself from the impulsion of just throwing away the .hbm.xml files and grab ActiveRecord or FluentNHibernate several times a day.
So, here is my dilemma: Should I go with my heart of "Just get this damn thing done!"; Or, should I follow the "Good practice guideline" to suffer the pain now and get relatively easy time later on?
Any comments?
Please note that any classes related to an ORM should not necessary be treated as "business object" classes or exposed to your UI. They should be considered part of your data layer. This pattern is not really unique to ActiveRecord. In general, you want your business layer to know as little as possible regarding the fact that there is an ORM beneath it, and you don't want your UI to know about your data layer. You also want to consider DTOs.
Fluent NHibernate solves the problem of having weakly typed XML which can be error prone to refactor.
While there can be downsides of adopting something like ActiveRecord, it seems like an appropriate solution in your case.
The best reason to use .hbm.xml files is if you are going to code generate them from your database (using something like CodeSmith). Hand coding the .hbm.xml files is rarely the best option.