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POPreventing delete/insert when modifying many-to-many relationship with NHibernate
 

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  1. POPreventing delete/insert when modifying many-to-many relationship with NHibernate
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    <p>In my domain model a User is associated with many Places - the relationship is modelled via a UserPlace class and a mapping (with FluentNHibernate) as follows (the User has a collection of UserPlace called <em>Neighbourhood</em>:</p> <pre><code>public class UserMap : ClassMap&lt;User&gt; { HasMany(x =&gt; x.Neighbourhood) .Component(c =&gt; { c.Map(x =&gt; x.IsDefault).Not.Nullable(); c.Map(x =&gt; x.Selected).Not.Nullable().Default("0"); c.References(x =&gt; x.Place).Fetch.Join(); } ).Not.LazyLoad().Cascade.SaveUpdate(); } </code></pre> <p>Whenever I modify any UserPlace entity belonging to a user and then persist the user to the db, <em>all UserPlace rows for that user are deleted and then re-inserted</em>.</p> <p>I assume this is because NHibernate doesn't know how to uniquely identify one of these rows from another. In other words, the component in my mapping doesn't have a key as such.</p> <p>A primary key can be formed by combining the User_id and Place_id columns in the table that stores the relationship between these two entities. How can I set up this key using Fluent? And will this solve the delete-and-re-insert behaviour that I'm seeing?</p> <p><strong>EDIT:</strong> I asked on NHUsers about this and Fabio Maulo suggested using an IdBag. This isn't supported in Fluent NHibernate as far as I can tell - and components don't allow identifiers. How else can I map this many-to-many relationship and prevent the delete-all-reinsert-all issue?</p> <p><strong>EDIT 2:</strong> Here are the tables that NH generate based on my mappings</p> <pre><code>CREATE TABLE [dbo].[User]( [Id] [uniqueidentifier] NOT NULL, --- a bunch of unimportant fields CONSTRAINT [PK__User] PRIMARY KEY CLUSTERED ([Id] ASC)) CREATE TABLE [dbo].[Neighbourhood]( [User_id] [uniqueidentifier] NOT NULL, [IsDefault] [bit] NOT NULL, [Place_id] [int] NOT NULL, [Selected] [bit] NOT NULL) CREATE TABLE [dbo].[Place]( [Id] [int] IDENTITY(1000,1) NOT NULL, --- a bunch of unimportant fields CONSTRAINT [PK_Place] PRIMARY KEY CLUSTERED ([Id] ASC)) </code></pre> <p>There is a FK relationship between User.Id and Neighbourhood.User_Id and between Neighbourhood.Place_id and Place.Id</p>
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    1. COIt may help to show the sql used to create the tables in question. I'm having a hard time visualizing the tables. It sounds like you need a composite id in the mapping of a UserPlace. It may be easier to provide you with an alternate mapping if I could see the tables.
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    2. COThanks for your comment. I have updated the question with table definitions (I cut out non-important columns for brevity)
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