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POHow correctly do a bi-directional many-to-many in nHibernate
 

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  1. POHow correctly do a bi-directional many-to-many in nHibernate
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    <p>I'm trying to get my head around how to correctly use many-to-many relationships in NHibernate in DotNet 4.5. What Collection types to use and what to init them as.</p> <p>Scenario: Modeling OrgUnits and Positions. There is a many to many relationship with the following tables:</p> <p>OrgUnits Positions OrgUnitPositions</p> <p>I'm using bi-directional setters so that no matter if I go orgUnit.AddPosition(position) OR position.AddOrgUnit(orgUnit), the relationship should be added to both collections.</p> <p>Here is my example code </p> <pre><code>public class Position { public Position() { OrgUnits = new List&lt;OrgUnit&gt;(); } public virtual ICollection&lt;OrgUnit&gt; OrgUnits { get; set; } public virtual void AddOrgUnit(OrgUnit orgUnit) { if (!OrgUnits.Contains(orgUnit)) { OrgUnits.Add(orgUnit); if (!orgUnit.Positions.Contains(this)) orgUnit.AddPosition(this); } } public class PositionMap : ClassMap&lt;Position&gt; { public PositionMap() { HasManyToMany(x =&gt; x.OrgUnits) .ChildKeyColumn("OrgUnitID") .ParentKeyColumn("PositionID") .Table("OrgUnitPositions") .Fetch.Select() .Cascade.AllDeleteOrphan() .AsBag() .Inverse(); } } public class OrgUnit { public OrgUnit() { Positions = new HashSet&lt;Position&gt;(); } public virtual ICollection&lt;Position&gt; Positions { get; set; } public virtual void AddPosition(Position value) { if (!Positions.Contains(value)) { Positions.Add(value); if (!value.OrgUnits.Contains(this)) value.AddOrgUnit(this); } } } public class OrgUnitMap : ClassMap&lt;OrgUnit&gt; { public OrgUnitMap() { HasManyToMany(x =&gt; x.Positions) .ChildKeyColumn("PositionID") .ParentKeyColumn("OrgUnitID") .Table("OrgUnitPositions") .Fetch.Select() .Cascade.AllDeleteOrphan() .AsSet() ; } } </code></pre> <p>My problem is that when I call orgUnit.AddPosition(position)), in some circumstancs, this line in Position.AddOrgUnit: if (!value.Positions.Contains(this)) returns false, even though i can see in the debuger that is does contain the org unit. This leads to it being added twice and then a duplicate key exception occurs on save.</p> <p>I've tried all sorts of things (my original collections where lists/ILists) but I suspect that my collection type (ilist/iset/etc) is the cause - hoping someone can point me in the direction of which collection types to use, what to initlise them as, etc.</p> <p>If I call position.AddOrgUnit(orgUnit); instead of orgUnit.AddPosition, everything works.</p> <p>--- Update</p> <p>In response to comments, I changed theAddOrgUnit in Position.cs as follows:</p> <pre><code>public virtual void AddOrgUnit(OrgUnit orgUnit) { if (!OrgUnits.Contains(orgUnit)) { OrgUnits.Add(orgUnit); foreach (Position p in orgUnit.Positions) { System.Console.WriteLine(string.Format("{0}", ReferenceEquals(p, this))); } if (!value.Positions.Contains(this)) { value.AddPosition(this); } } } </code></pre> <p>and here is what i found - keeping in mind that orgUnit.positions only contains 1 item and the for-each is just to get access to that item in the debugger.</p> <p>ReferenceEquals(p, this) <strong>false</strong></p> <p>p.GetHashCode() <strong>40148707</strong></p> <p>this.GetHashCode() <strong>53416668</strong></p> <p>this.ID <strong>{8386857d-a52e-4f17-8094-a231003299b5}</strong></p> <p>p.ID <strong>{8386857d-a52e-4f17-8094-a231003299b5}</strong></p> <p>p.Description <strong>"bob"</strong></p> <p>this.Description <strong>"bob"</strong></p> <p>p.description = "Jane"</p> <p>this.Description <strong>"Jane"</strong></p> <p>p.description <strong>"Jane"</strong></p> <p>This is the strange one! The hashCodes are different, yet it appears to be the same instance of the same object. IE, if I change a property on the "this" version, it changes in the "p" version.</p> <p>Finally, ReferenceEquals(p.ReportsToPosition, this.ReportsToPosition) <strong>true</strong></p> <p>Which tends to indicate they are from the same hibernate session? (ie, the parents are the same)</p> <hr> <p>Here is my calling code, we use StrctureMap for IoC, with ISession being injected into the repos. I have changed my code to pass in the BLL, which guarantees same Isession because the repositories are injected into it.</p> <p>Strangely, the only line the causes the error is the one indicated, and if I remove lines above, it works perfectly too!</p> <pre><code>[TestMethod] public void CreateExampleOrgStructure() { OrgStructureLogic osl = (OrgStructureLogic)ObjectFactory.GetInstance(typeof(OrgStructureLogic)); Domain domain = osl.GetNewDomain(DomainTypeEnum.ReportingLines); domain.Name = string.Format("blah.Net - {0} {1}", DateTime.Now.ToLongDateString(), DateTime.Now.ToLongTimeString()); OrgUnit ouGlobal = domain.RootOrgUnit; ouGlobal.Name = "Global"; OrgUnit ouTech = GetNewOrgUnit(ouGlobal, "Technology", osl); AddPositionToOrgUnit(ouTech, "Chief Technology Officer", osl); AddPositionToOrgUnit(ouTech, "General Manager Technology", osl); OrgUnit ouFeatureDevelopers = GetNewOrgUnit(ouTech, "Feature Dev", osl); AddPositionToOrgUnit(ouFeatureDevelopers, "Senior Feature Developer", osl); AddPositionToOrgUnit(ouFeatureDevelopers, "Feature Developer", osl); OrgUnit ouSupportDevelopers = GetNewOrgUnit(ouTech, "Support Dev", osl); AddPositionToOrgUnit(ouSupportDevelopers, "Senior Support Developer", osl); AddPositionToOrgUnit(ouSupportDevelopers, "Support Developer", osl); OrgUnit ouDevManagement = GetNewOrgUnit(ouTech, "Management", osl); AddPositionToOrgUnit(ouDevManagement, "Dev Manager", osl); /* This is the problem!!!!*/ AddPositionToOrgUnit(ouDevManagement, "Application Architect", osl); osl.SaveDomain(domain); } </code></pre> <p>Even stranger is that I can also fix the problem be changing </p> <pre><code>private void AddPositionToOrgUnit(OrgUnit orgUnit, string positionName, OrgStructureLogic osl) { orgUnit.AddPosition(GetPositionByName(positionName), osl); } </code></pre> <p>to </p> <pre><code>private void AddPositionToOrgUnit(OrgUnit orgUnit, string positionName, OrgStructureLogic osl) { Position position = GetPositionByName(positionName, osl); position.AddOrgUnit(orgUnit); } </code></pre>
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    1. USDave
    1. USDave
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    1. CODid you try once to compare the Ids of the entities instead of the references? I encountered this kind of problems before, especially when NHibernate generates Proxy-Classes. Sometimes I have overwritten `Equals` (and `GetHashCode`) where I compared the Ids of the entity.
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      1. POHow correctly do a bi-directional many-to-many in nHibernate
      1. USsl3dg3
    2. COCan you show the code where you call `orgUnit.AddPosition(position)`? My guess is that `orgUnit` and `position` are from two different NHibernate sessions. When you see it in the debugger, could you check to see whether the two instances that you believe to be equal actually do `ReferenceEquals` or not?
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      1. POHow correctly do a bi-directional many-to-many in nHibernate
      1. USDaniel Schilling
    3. CO@sl3dg3 I have added the result of the ID comparison - they are the same. I'm hesitant in overwriting Equals/GetHashCode because I like creating graphs of empty objects then saving them by calling save(rootObject) - ie, I want to be able to compare when the objects have a null ID.
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      1. POHow correctly do a bi-directional many-to-many in nHibernate
      1. USDave
 

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