I&#39;m trying to figure out how to use NHibernate configuration with mapping to update table schemas, rather than dropping and recreating them.

Currently I&#39;m using the `NHibernate.Tool.hbm2ddl.SchemaExport` obj with FluentNHibernate to generate the database schema for a mysql database.  While I can&#39;t say it&#39;s a huge problem, whenever I call `SchemaExport.Execute` on the database, it&#39;s going to drop all the tables and then recreate them.  

What would be way cooler is if I could just have it update the existing table structures retaining data where possible.  But I don&#39;t really want to use a commerical product, or a code generator, because I don&#39;t like code generation in general, and I don&#39;t need this enough that I would consider paying for it. So hopefully any answer would keep these caveats in mind.

How to update database table schemas with NHibernate schema generation?

I would create a QueryOver like this

    SELECT *
    FROM Table
    WHERE Field IN (1,2,3,4,5)

I&#39;ve tried with `Contains` method but I&#39;ve encountered the Exception 
&gt;&quot;System.Exception: Unrecognised method call: System.String:Boolean Contains(System.String)&quot;

Here my code

    var qOver = _HibSession.QueryOver&lt;MyModel&gt;(() =&gt; baseModel)                                                                
      .JoinAlias(() =&gt; baseModel.Submodels, () =&gt; subModels)
      .Where(() =&gt; subModels.ID.Contains(IDsSubModels))
      .List&lt;MyModel&gt;();


NHibernate using QueryOver with WHERE IN

I have an **empty** app.config file, but I still get NHibernate debug logs

    NHibernate: SELECT this_.LogID as LogID71_0_, this_.Level as Level71_0_, this_.Message as Message71_0_, this_.EventTime as EventTime71_0_, this_.Component as ...

I tried adding a log4net configuration with an ERROR log level, but no use. How can I stop these log messages?

The thing I&#39;m puzzled about is why do these appear in the first place if I have an empty app.config to being with. It doesn&#39;t make sense to me that I have to configure it not to print these messaages - the default should be off. Could it be my code is setting them on programatically somehow? What should I look for?

Disable NHibernate logging

How to configure Fluent NHibernate to output queries to Trace or Debug instead of Console?
I&#39;m using `MsSqlConfiguration.MsSql2008.ShowSql()` but it has no parameters and I can&#39;t find anything on Google.


How to configure Fluent NHibernate to output queries to Trace or Debug instead of Console?

Is there a way to persist an enum to the DB using NHibernate? That is have a table of both the code and the name of each value in the enum.

I want to keep the enum without an entity, but still have a foreign key (the int representation of the enum) from all other referencing entities to the enum&#39;s table.

How to persist an enum using NHibernate

I have a mapping along the lines of this.

    &lt;hibernate-mapping xmlns=&quot;urn:nhibernate-mapping-2.2&quot; namespace=&quot;Model.Entities&quot; schema=&quot;etl&quot; assembly=&quot;Model&quot; default-lazy=&quot;false&quot;&gt;
      &lt;class name=&quot;Model.Entities.DataField, Model&quot; table=&quot;mdm_field&quot;&gt;
        &lt;id name=&quot;FieldId&quot; column=&quot;field_id&quot; type=&quot;int&quot;&gt;
          &lt;generator class=&quot;native&quot; /&gt;
        &lt;/id&gt;
        &lt;many-to-one name=&quot;KeyField&quot; class=&quot;Model.Entities.Key, Model&quot; column=&quot;field_id&quot; /&gt;
      &lt;/class&gt;
    &lt;/hibernate-mapping&gt;

Now in the database the field_id in the mdm_field table sometimes has a value that does not exist in the related key_field table, so it is basically broken referential integrity. Because of this when I load the entity I get an error &quot;No row with the given identifier exists&quot;. How do I configure the mapping to work with this situation so it will not die on this situation.



nHibernate, No row with the given identifier exists

Is there any elegant way of combining &#39;like&#39; and &#39;or&#39; when i&#39;m using queryover API?
for &#39;like&#39; there is something like: 

     query.WhereRestrictionOn(x=&gt;x.Code).IsLike(codePart)
for &#39;or&#39; i can do something like: 

    query.Where( x=&gt;x.Code == codePart || x.Description== codePart)
but how can I create a query like this:

&gt; select * from n where code like
&gt; &#39;%abc%&#39; or description like &#39;%abc%&#39;



queryover and (x like &#39;a&#39; or y like &#39;a&#39;)

I have this Repository method

        public IList&lt;Message&gt; ListMessagesBy(string text, IList&lt;Tag&gt; tags, int pageIndex, out int count, out int pageSize)
        {
            pageSize = 10;
            var likeString = string.Format(&quot;%{0}%&quot;, text);
            var query = session.QueryOver&lt;Message&gt;()
                .Where(Restrictions.On&lt;Message&gt;(m =&gt; m.Text).IsLike(likeString) || 
                Restrictions.On&lt;Message&gt;(m =&gt; m.Fullname).IsLike(likeString));

            if (tags.Count &gt; 0)
            {
                var tagIds = tags.Select(t =&gt; t.Id).ToList();
                query
                    .JoinQueryOver&lt;Tag&gt;(m =&gt; m.Tags)
                    .WhereRestrictionOn(t =&gt; t.Id).IsInG(tagIds);
            }            

            count = 0;
            if(pageIndex &lt; 0)
            {
                count = query.ToRowCountQuery().FutureValue&lt;int&gt;().Value;
                pageIndex = 0;
            }
            return query.OrderBy(m =&gt; m.Created).Desc.Skip(pageIndex * pageSize).Take(pageSize).List();
        }

You supply a free text search string and a list of Tags.
The problem is that if a message has more then one tag it is listed duplicated times. 
I want a distinct result based on the Message entity. I&#39;ve looked at

    Projections.Distinct
But it requires a list of Properties to to the distinct question on. This Message is my entity root there most be a way of getting this behaviour without supplying all of the entity properties?

Thanks in advance, Anders

How to get a distinct result with nHibernate and QueryOver API?

What&#39;s the simplest way to use [MiniProfiler][1]&#39;s database profiling with NHibernate? In order for the profiler to work, I need to wrap the `DbConnection` that NHibernate uses in a `ProfiledDbConnection`. 

I&#39;m not too familiar with the internals of NHibernate, so I don&#39;t know where all the extensibility points are. (I noticed that an NHibernate `ISession` has a `Connection` property, but it is read-only.)

[1]: http://miniprofiler.com/

Using MiniProfiler&#39;s database profiling with NHibernate

Can anyone explain in simple words what First and Second Level caching in Hibernate/NHibernate are?

What are the First and Second Level caches in (N)Hibernate?

One of the things that get me thoroughly confused is the use of `session.Flush`,in conjunction with `session.Commit`, and `session.Close`.

Sometimes `session.Close` works, e.g., it commits all the changes that I need. I know I need to use commit when I have a transaction, or a unit of work with several creates/updates/deletes, so that I can choose to rollback if an error occurs.

But sometimes I really get stymied by the logic behind `session.Flush`. I have seen examples where you have a `session.SaveOrUpdate()` followed by a flush, but when I remove Flush it works fine anyway. Sometimes I run into errors on the Flush statement saying that the session timed out, and removing it made sure that I didn&#39;t run into that error.

Does anyone have a good guideline as to where or when to use a Flush? I&#39;ve checked out the NHibernate documentation for this, but I still can&#39;t find a straightforward answer.

NHibernate ISession Flush: Where and when to use it, and why?

Now, before you say it: I **did** Google and my `hbm.xml` file **is** an Embedded Resource. 

Here is the code I am calling:

    ISession session = GetCurrentSession();
    var returnObject =  session.Get&lt;T&gt;(Id);

Here is my mapping file for the class:

&lt;!-- language: lang-xml --&gt;

    &lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot; ?&gt;
    &lt;hibernate-mapping xmlns=&quot;urn:nhibernate-mapping-2.2&quot;&gt;
      &lt;class name=&quot;HQData.Objects.SubCategory, HQData&quot; table=&quot;SubCategory&quot; lazy=&quot;true&quot;&gt;
        &lt;id name=&quot;ID&quot; column=&quot;ID&quot; unsaved-value=&quot;0&quot;&gt;
          &lt;generator class=&quot;identity&quot; /&gt;
        &lt;/id&gt;
    
        &lt;property name=&quot;Name&quot; column=&quot;Name&quot; /&gt;
        &lt;property name=&quot;NumberOfBuckets&quot; column=&quot;NumberOfBuckets&quot;  /&gt;
        &lt;property name=&quot;SearchCriteriaOne&quot; column=&quot;SearchCriteriaOne&quot; /&gt;
        
        &lt;bag name=&quot;_Businesses&quot; cascade=&quot;all&quot;&gt;
          &lt;key column=&quot;SubCategoryId&quot;/&gt;
          &lt;one-to-many 
             class=&quot;HQData.Objects.Business, HQData&quot;/&gt;
        &lt;/bag&gt;
    
        &lt;bag name=&quot;_Buckets&quot; cascade=&quot;all&quot;&gt;
          &lt;key column=&quot;SubCategoryId&quot;/&gt;
          &lt;one-to-many
             class=&quot;HQData.Objects.Bucket, HQData&quot;/&gt;
        &lt;/bag&gt;
    
      &lt;/class&gt;
    &lt;/hibernate-mapping&gt;

Has anyone run to this issue before?

Here is the full error message:

&gt; &lt;pre&gt;MappingException: No persister for:  HQData.Objects.SubCategory]NHibernate.Impl.SessionFactoryImpl.GetEntityPersister(String entityName, Boolean throwIfNotFound)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionFactoryImpl.cs:766 NHibernate.Impl.SessionFactoryImpl.GetEntityPersister(String entityName)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionFactoryImpl.cs:752 NHibernate.Event.Default.DefaultLoadEventListener.OnLoad(LoadEvent event, LoadType loadType)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Event\Default\DefaultLoadEventListener.cs:37 NHibernate.Impl.SessionImpl.FireLoad(LoadEvent event, LoadType loadType)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionImpl.cs:2054 NHibernate.Impl.SessionImpl.Get(String entityName, Object id)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionImpl.cs:1029 NHibernate.Impl.SessionImpl.Get(Type entityClass, Object id)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionImpl.cs:1020 NHibernate.Impl.SessionImpl.Get(Object id)
 in c:\CSharp\NH2.0.0\nhibernate\src\NHibernate\Impl\SessionImpl.cs:985 HQData.DataAccessUtils.NHibernateObjectHelper.LoadDataObject(Int32 Id)
 in C:\Development\HQChannelRepo\HQ Channel Application\HQChannel\HQData\DataAccessUtils\NHibernateObjectHelper.cs:42 HQWebsite.LocalSearch.get_subCategory()
 in C:\Development\HQChannelRepo\HQ Channel Application\HQChannel\HQWebsite\LocalSearch.aspx.cs:17 HQWebsite.LocalSearch.Page_Load(Object sender, EventArgs e)
 in C:\Development\HQChannelRepo\HQ Channel Application\HQChannel\HQWebsite\LocalSearch.aspx.cs:27 System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +15 System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +33 System.Web.UI.Control.OnLoad(EventArgs e) +99 System.Web.UI.Control.LoadRecursive() +47 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1436&lt;/pre&gt;

**Update**, here&#39;s what the solution for *my* scenario was: I had changed some code and I wasn&#39;t adding the Assembly to the config file during runtime. 

NHibernate.MappingException: No persister for: XYZ

As someone who hasn&#39;t used either technology on real-world projects I wonder if anyone knows how these two complement each other and how much their functionalities overlap?

NHibernate vs LINQ to SQL

Not sure how I can fix this, trying to do a unit test on the method &quot;GetByTitle&quot;

Here are my definitions:

    public class ArticleDAO :  GenericNHibernateDAO(IArticle, int&gt;, IArticleDAO
    {
        public IArticle GetByTitle(string title)
        {
            IQuery query = Session.CreateQuery(&quot;...&quot;)
            return query.UniqueResult&lt;IArticle&gt;();
        }
    }
    
    public interface IArticleDAO
    {
        IArticle GetByTitle(string title);
    }

unit test:

    [Test]
    public void can_load_by_title()
    {
        _mockDaoFactory.Setup(x =&gt; x.GetArticleDao())
                                    .Returns(_mockArticleDao.Object);
        _mockArticleDao.Setup(x =&gt; x.GetByTitle(&quot;some title&quot;))
                                    .Returns(article1.Object);
    
        _articleManager.LoadArticle(&quot;some title&quot;);

        Assert.IsNotNull(_articleManager.Article);
    }

Running the test gives me the error:

    System.ArgumentException: Invalid setup on a non-overridable member:
    x =&gt; x.GetByTitle(&quot;some title&quot;)

&lt;b&gt;Update&lt;/b&gt;

My `[Setup]` looks like:

    [Setup]
    public void SetUp()
    {
         _mockDaoFactory = new Mock&lt;IDaoFactory&gt;();
         _mockArticleDao = new Mock&lt;ArticleDao&gt;();
    
         _articleManager = new ArticleManager(_mockDaoFactory.Object);    
    }

Moq: Invalid setup on a non-overridable member: x =&gt; x.GetByTitle(&quot;asdf&quot;)

What&#39;s the difference between a list, set and bag in the NHibernate mapping file? How does each relate to the .NET collections?

List vs Set vs Bag in NHibernate

For example, I want to populate a gridview control in an ASP.NET web page with only the data necessary for the # of rows displayed. How can NHibernate support this?

How can you do paging with NHibernate?

I&#39;m writing an integration test where I will be inserting a number of objects into a database and then checking to make sure whether my method retrieves those objects.

My connection to the database is through NHibernate...and my usual method of creating such a test would be to do the following:

    NHibernateSession.BeginTransaction();
    
    //use nhibernate to insert objects into database
    //retrieve objects via my method
    //verify actual objects returned are the same as those inserted
    
    NHibernateSession.RollbackTransaction();

However, I&#39;ve recently found out about [TransactionScope][1] which apparently can be used for this very purpose...

Some [example code I&#39;ve found][2] is as follows:

    public static int AddDepartmentWithEmployees(Department dept)
    {
    
        int res = 0;
    
        DepartmentAdapter deptAdapter = new DepartmentAdapter();
        EmployeeAdapter empAdapter = new EmployeeAdapter();
        using (TransactionScope txScope = new TransactionScope())
        {
    
            res += deptAdapter.Insert(dept.DepartmentName);
            //Custom method made to return Department ID 
            //after inserting the department &quot;Identity Column&quot;
            dept.DepartmentID = deptAdapter.GetInsertReturnValue();
            foreach(Employee emp in dept.Employees)
            {
    
                emp.EmployeeDeptID = dept.DepartmentID;
                res += empAdapter.Insert(emp.EmployeeName, emp.EmployeeDeptID);
    
            }
            txScope.Complete();
    
        }
        return res;
    
    }

I believe that if I don&#39;t include the line `txScope.Complete()` that the data inserted will be rolled back. But unfortunately I don&#39;t understand how that is possible... how does the `txScope` object keep a track of the `deptAdapter` and `empAdapter` objects and their transactions on the database.

I feel like I&#39;m missing a bit of information here...am I really able to replace my `BeginTransaction()` and `RollbackTransaction(`) calls by surrounding my code using `TransactionScope`?

If not, how then does `TransactionScope` work to roll back transactions?

  [1]: http://msdn.microsoft.com/en-us/library/system.transactions.transactionscope.aspx
  [2]: http://dotnetslackers.com/articles/ado_net/Managing_Transactions_using_TransactionScope.aspx

How does TransactionScope roll back transactions?

I have a HQL query that can generate either an IList of results, or an IEnumerable of results. 

However, I want it to return an array of the Entity that I&#39;m selecting, what would be the best way of accomplishing that? I can either enumerate through it and build the array, or use CopyTo() a defined array.

Is there any better way? I went with the CopyTo-approach.

Best way to convert IList or IEnumerable to Array

Has anyone implemented this, or know if it would be difficult to implement this/have any pointers?

    public static SpatialRelationCriterion IsWithinDistance(string propertyName, object anotherGeometry, double distance)
    {
        // TODO: Implement
        throw new NotImplementedException();
    }

from NHibernate.Spatial.Criterion.SpatialRestrictions

I can use &quot;where NHSP.Distance(PROPERTY, :point)&quot; in hql. But want to combine this query with my existing Criteria query.

for the moment I&#39;m creating a rough polygon, and using 

    criteria.Add(SpatialRestrictions.Intersects(&quot;PROPERTY&quot;, myPolygon));

***EDIT***
Got a prototype working by overloading constructor on SpatialRelationCriterion, adding new SpatialRelation.Distance

    public static SpatialRelationCriterion IsWithinDistance(string propertyName, object anotherGeometry, double distance)
    		{
                return new SpatialRelationCriterion(propertyName, SpatialRelation.Distance, anotherGeometry, distance);
    		}

added a new field to SpatialRelationCriterion

    private readonly double? distance;

    public SpatialRelationCriterion(string propertyName, SpatialRelation relation, object anotherGeometry, double distance)
                : this(propertyName, relation, anotherGeometry)
            {
                this.distance = distance;
            }

Edited ToSqlString

    object secondGeometry = Parameter.Placeholder;
                    if (!(this.anotherGeometry is IGeometry))
                    {
                        secondGeometry = columns2[i];
                    }
    
                    if (distance.HasValue)
                    {
                        builder.Add(spatialDialect.GetSpatialRelationString(columns1[i], this.relation, secondGeometry, distance.Value, true));
                    }
                    else
                    {
                        builder.Add(spatialDialect.GetSpatialRelationString(columns1[i], this.relation, secondGeometry, true));
                    }

overloaded ISpatialDialect.GetSpatialRelationString

implemented overload in MsSql2008SpatialDialect

    public SqlString GetSpatialRelationString(object geometry, SpatialRelation relation, object anotherGeometry, double distance, bool criterion)
            {
                var x = new SqlStringBuilder(8)
                               .AddObject(geometry)
                               .Add(&quot;.ST&quot;)
                               .Add(relation.ToString())
                               .Add(&quot;(&quot;)
                               .AddObject(anotherGeometry)
                               .Add(&quot;)&quot;);
    
                if (criterion)
                {
                    x.Add(&quot; &lt; &quot;);
                    x.AddObject(distance.ToString());
                }
    
                return x.ToSqlString();
            }

Not sure why AddParameter not being used?

Criteria SpatialRestrictions.IsWithinDistance NHibernate.Spatial

How do I use the Inverse Attribute? If I am not mistaken, for one to many relationships the inverse attribute must be set to true. For many-to-many relationships, one of the entity class inverse attributes must be set to true and another set to false. 

Anyone can shed some lights on this?

Inverse Attribute in NHibernate

I need to know what is the difference between JoinQueryOver and JoinAlias, and when to use each?

What is the difference between JoinQueryOver and JoinAlias?

I notice sometimes with my parent/child objects or many-to-many relationships, I need to call either `SaveOrUpdate` or `Merge`. Usually, when I need to call `SaveOrUpdate`, the exception I get on calling `Merge` has to do with transient objects not being saved first.

Please explain the difference between the two.

What&#39;s the difference between session.Merge and session.SaveOrUpdate?

Question says it all really, the default is for it to map as a `string` but I need it to map as an `int`.

I&#39;m currently using `PersistenceModel` for setting my conventions if that makes any difference. Thanks in advance.

**Update**
Found that getting onto the latest version of the code from the trunk resolved my woes.

How do you map an enum as an int value with fluent NHibernate?

I have a class called ReportRequest as:

    public class ReportRequest
    {
        Int32 templateId;
        List&lt;Int32&gt; entityIds;

        public virtual Int32? Id
        {
            get;
            set;
        }

        public virtual Int32 TemplateId
        {
            get { return templateId; }
            set { templateId = value; }
        }

        public virtual List&lt;Int32&gt; EntityIds
        {
            get { return entityIds; }
            set { entityIds = value; }
        }

        public ReportRequest(int templateId, List&lt;Int32&gt; entityIds)
        {
            this.TemplateId = templateId;
            this.EntityIds = entityIds;
        }
    }

It is mapped using Fluent Hibernate as:

    public class ReportRequestMap : ClassMap&lt;ReportRequest&gt;
    {
        public ReportRequestMap()
        {
            Id(x =&gt; x.Id).UnsavedValue(null).GeneratedBy.Native();
            Map(x =&gt; x.TemplateId).Not.Nullable();            
            HasMany(x =&gt; x.EntityIds).Table(&quot;ReportEntities&quot;).KeyColumn(&quot;ReportRequestId&quot;).Element(&quot;EntityId&quot;).AsBag().Cascade.AllDeleteOrphan();
        }
    }

Now, I create an object of this class as 

    ReportRequest objReportRequest = new ReportRequest(2, new List&lt;int&gt;() { 11, 12, 15 });

and try to Save the object in database using 

    session.Save(objReportRequest);

I get the following error:
*&quot;Unable to cast object of type &#39;NHibernate.Collection.Generic.PersistentGenericBag`1[System.Int32]&#39; to type &#39;System.Collections.Generic.List`1[System.Int32]&#39;.*&quot;


I am not sure if I have mapped the property EntityIds correctly.
Please guide.

Thank you!

Unable to cast object of type NHibernate.Collection.Generic.PersistentGenericBag to List

I&#39;m using NHibernate 2.1.2.400 that is referencing log4net 1.2.10.0.
In the same project, I also use the simply accounting SDK, sadly it is still using log4net 1.2.9.0.

So I can get NHibernate to work if I reference log4net 1.2.10.0 but the simplySDK don&#39;t work.  And vice versa...

I&#39;m guessing most of the problems come from the fact that log4net has changed its assembly key. I tried using a binding redirection without success: the 2 DLLs do not have the same key.

I&#39;m considering recompiling NHibernate to use log4net 1.2.9.0 but it seems like the wrong thing to do and my feeling is that Simply Accounting won&#39;t be updating their SDK to use log4net 1.2.10.0 anytime soon.

What is the best way to handle this? Is it possible to resolve at all?

Referencing 2 different versions of log4net in the same solution

I have a parent object which has a one to many relationship with an IList of child objects. What is the best way to delete the child objects? I am not deleting the parent. My parent object contains an IList of child objects. Here is the mapping for the one to many relationship:

    &lt;bag name=&quot;Tiers&quot; cascade=&quot;all&quot;&gt;
      &lt;key column=&quot;mismatch_id_no&quot; /&gt;
      &lt;one-to-many class=&quot;TGR_BL.PromoTier,TGR_BL&quot;/&gt;
    &lt;/bag&gt;
If I try to remove all objects from the collection using clear(), then call SaveOrUpdate(), I get this exception:

    System.Data.SqlClient.SqlException: Cannot insert the value NULL into column

If I try to delete the child objects individually then remove them from the parent, I get an exception: 

    deleted object would be re-saved by cascade

This is my first time dealing with deleting child objects in NHibernate. What am I doing wrong?

edit: Just to clarify  - I&#39;m NOT trying to delete the parent object, just the child objects. I have the relationship set up as a one to many on the parent. Do I also need to create a many-to-one relationship on the child object mapping?

How to delete child object in NHibernate?

NHibernate eager loading can be done using `Fetch` and `FetchMany`, as described in [NHibernate Linq Eager Fetching](http://mikehadlow.blogspot.com/2010/08/nhibernate-linq-eager-fetching.html) on Mike Hadlow&#39;s blog.

What is the difference between these two methods and under what circumstance would each be used?

Fetch vs FetchMany in NHibernate Linq provider

I was wondering if anyone has a good solution to a problem I&#39;ve encountered numerous times during the last years.

I have a shopping cart and my customer explicitly requests that it&#39;s order is significant. So I need to persist the order to the DB.

The obvious way would be to simply insert some OrderField where I would assign the number 0 to N and sort it that way.

But doing so would make reordering harder and I somehow feel that this solution is kinda fragile and will come back at me some day.

(I use C# 3,5 with NHibernate and SQL Server 2005)


Thank you 

Best way to save a ordered List to the Database while keeping the ordering

I have been trying to get to grips with Hibernate&#39;s inverse attribute, and it seems to be just one of those things that is conceptually difficult. 

The gist that I get is that when you have a parent entity (e.g. Parent) that has a collection of Child objects using a **one-to-many** mapping, setting inverse=true on the mapping tells Hibernate that &#39;the other side (the Child) has responsibility to update itself to maintain the foreign key reference in its table&#39;. 

Doing this appears to have 2 benefits when it comes to adding Children to the collection in your code, and then saving the Parent (with cascade-all set): [you save an unneccessary hit on the database][1] (because without inverse set, Hibernate thinks it has two places to update the FK relationship), and according to the official docs:

&gt;  If the &lt;key&gt; column of a
&gt; &lt;one-to-many&gt; association is declared
&gt; NOT NULL, NHibernate may cause
&gt; constraint violations when it creates
&gt; or updates the association. To prevent
&gt; this problem, you must use a
&gt; bidirectional association with the
&gt; many valued end (the set or bag)
&gt; marked as inverse=&quot;true&quot;.

This all seems to make sense so far. What I don&#39;t get is this: when would you **NOT** want to use inverse=true on a one-to-many relationship?

  [1]: http://nhprof.com/Learn/Alert?name=SuperfluousManyToOneUpdate

When to use inverse=false on NHibernate / Hibernate OneToMany relationships?

I&#39;ve seen some examples in which `decimal` is used in NHibernate projects for mapping to whole number columns in Oracle. Right now I&#39;m using `int` and `long` in my program. 

What are the advantages of `decimal` over `int`/`long`? Does it perform better?

Which .NET data type is best for mapping the NUMBER Oracle data type in NHibernate?

What is the difference between SaveOrUpdate and Save/Update in NHibernate. Why wouldnt you just always use SaveOrUpdate? Also, what is the point of SaveOrUpdateCopy?

SaveOrUpdate Vs Update and Save in NHibernate

I know how to log the SQL to log4net/NLog/trace window at runtime with the `show_sql` configuration option.

What I&#39;m looking for is a way to give a `Query&lt;T&gt;()` to NHibernate retrieve the generated SQL.

I&#39;ve looked through the Persister class, the Drivers, different Interceptors and Events. There are so many places to look, even narrowing down my search would be of great help.

How can I have NHibernate only generate the SQL without executing it?

I have an application that uses NHibernate as its ORM and sometimes it experiences performance issues due to how the data is being accessed by it. What kind of things can be done to improve the performance of NHibernate? (Please limit to one recommendation per answer)


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