R – Fluent NHibernate Automapping Bi-directional relationships

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I am trying to automap my domain model using fluent nhibernate. In this particular case I have a bidirectional one-to-many relationship that i need to map. Problem is that it doesn't automatically realize it as a bidirectional relation but as two different relations altogether and creates a separate foreign key for each.

How do I tell fluent nhibernate that it is the same relation? I hope i am being clear enough.

Best Answer

You can override the automap using the 1.0RC. Try this example from SharpArchitecture's bi-directional mapping from Employee to Territory, where Territory is the inverse of the relationship:

   public class EmployeeMap : IAutoMappingOverride<Employee>
     {
        public void Override(AutoMap<Employee> mapping) {

        //... other omitted mappings...

        mapping.HasManyToMany<Territory>(x => x.Territories)
            .WithTableName("EmployeeTerritories")
            .WithParentKeyColumn("EmployeeID")
            .WithChildKeyColumn("TerritoryID")
            .AsBag();
    }
}

   public class TerritoryMap : IAutoMappingOverride<Territory>
{
    public void Override(AutoMap<Territory> mapping) {

        //... other omitted mappings...

        mapping.HasManyToMany<Employee>(x => x.Employees)
            .WithTableName("EmployeeTerritories")
            .Inverse()
            .WithParentKeyColumn("TerritoryID")
            .WithChildKeyColumn("EmployeeID")
            .AsBag();
    }
}

Related Solutions

Fluent NHibernate: How to create one-to-many bidirectional mapping

To get a bidirectional association with a not-null foreign key column in the Details table you can add the suggested Owner property, a References(...).CanNotBeNull() mapping in the DetailsMap class, and make the Summary end inverse.

To avoid having two different foreign key columns for the two association directions, you can either specify the column names manually or name the properties in a way that gives the same column name for both directions. In this case you I suggest renaming the Details.Owner property to Details.Summary.

I made the Summary id generated by increment to avoid problems when inserting into the table since Summary currenty has no columns besides id.

Domain:

public class Detail
{
    public int id { get; protected set; }
    public string ItemName { get; set; }

    // Renamed to use same column name as specified in the mapping of Summary.Details
    public Summary Summary {get; set;} 
}

public class Summary
{
    public Summary()
    {
        Details = new List<Detail>();
    }

    public int id { get; protected set; }
    public IList<Detail> Details { get; protected set; }
}

Mapping:

public class DetailMap : ClassMap<Detail>
{
    public DetailMap()
    {
        Id(x => x.id)
            .GeneratedBy.Native();

        Map(x => x.ItemName)
            .CanNotBeNull();

        References<Summary>(x => x.Summary)
            // If you don't want to rename the property in Summary,
            // you can do this instead:
            // .TheColumnNameIs("Summary_id")
            .CanNotBeNull();
    }
}

public class SummaryMap : ClassMap<Summary>
{
    public SummaryMap()
    {
        Id(x => x.id)
            .GeneratedBy.Increment();

        HasMany<Detail>(x => x.Details)
            .IsInverse()
            .AsBag(); // Use bag instead of list to avoid index updating issues
    }
}

Fluent NHibernate one to many uni-directional mapping

NHibernate doesn't support this mapping when you have a not-null constraint on your foreign key. If you remove that constraint, you'll see that NHibernate inserts the Comments with a null PostId, then updates them with the Id of the new Post.

You either need to:

Remove the not-null constraint and the Inverse call
Keep the constraint, and map the other side of the relationship (making this a bi-directional relationship, and allowing Inverse to work correctly)

This is covered in the NHibernate documentation for one-to-many's, see the Very Important Note at the end.

Best Answer

Related Solutions

Fluent NHibernate: How to create one-to-many bidirectional mapping

Fluent NHibernate one to many uni-directional mapping

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