Question

I have an entity that is made up of properties from two different tables as I described here and I’m running into problems when I try to insert a new item. When inserting I need to only update the fields in one of the two tables. Using the ReadOnly() method, I’ve been able to get NHibernate to ignore most of the fields from [RegistrationField] on save. However, I can’t get it to not try to save a new entry into [RegistrationField] for the foreign key, even though an entry already exists for that key.

My mapping for the class is:

public class RegistrationFieldMap : ClassMap<RegistrationField>
{
    public RegistrationFieldMap()
    {
        Table("AccountRegistrationField");

        Id(r => r.ID).Column("RegistrationID");
        Map(r => r.AccountID);
        Map(r => r.DefaultValue);
        Map(r => r.FieldID);
        Map(r => r.IsRequired);
        Map(r => r.Label);
        Map(r => r.Priority);
        Join("RegistrationField", t =>
        {
            t.Map(r => r.FieldType).ReadOnly();
            t.Map(r => r.HtmlID).ReadOnly();
        });
    }
}

When I run my test to verify the mapping, NHibernate tries to run the following two SQL statements:

INSERT INTO AccountRegistrationField (
    AccountID, 
    DefaultValue, 
    FieldID, 
    IsRequired, 
    Label, 
    Priority) 
VALUES (@p0, @p1, @p2, @p3, @p4, @p5); 
select SCOPE_IDENTITY();
@p0 = 1 [Type: Int32 (0)], 
@p1 = 'bar' [Type: String (4000)], 
@p2 = 1 [Type: Int32 (0)], 
@p3 = False [Type: Boolean (0)], 
@p4 = 'bar' [Type: String (4000)], 
@p5 = 1 [Type: Int32 (0)]

INSERT INTO RegistrationField (UserRegistrationField_id) VALUES (@p0);
@p0 = 12 [Type: Int32 (0)]

I only need it to run the first statement, since the [RegistrationField] table contains a static list of values and new items should never be added to it.

Any and all suggestions welcome.

Answer 1

OK, after thinking about Diego’s comment and getting a good nights sleep I figured out the correct way to implement this and get the result I want. Diego is right that I should be using Reference and not Join. My original reasoning for wanting to implement this as a join was a desire to avoid adding another level to my object graph. AccountRegistrationField is already a property on the Account object and I didn’t want to have to make a call like Account.AccountRegistrationField.RegistrationField.FieldType. I instead wanted the call to be Account.AccountRegistrationField.FieldType since the object I’ll really be operating on is the AccountRegistrationField object.

I was able to get this behavior by designing my AccountRegistrationField class a little better. I made the RegistrationField property private and added public properties on the AccountRegistrationField class to expose the fields that I needed. And then used Fluent NHibernate’s Reveal class to expose the private property to my mapping.

My AccountRegistrationField class ended up looking like this:

public class AccountRegistrationField
{
    public virtual int ID { get; set; }
    public virtual int AccountID { get; set; }
    public virtual string DefaultValue { get; set; }
    public virtual int FieldID { get; set; }
    public virtual string HtmlID 
    { 
        get { return RegistrationField.HtmlID; } 
    }
    public virtual bool IsRequired { get; set; }
    public virtual string Label { get; set; }
    public virtual int Priority { get; set; }
    public virtual string FieldType 
    { 
        get { return RegistrationField.FieldType; } 
    }

    private RegistrationField RegistrationField { get; set; }
}

And my mapping for AccountRegistrationField looks like:

public class AccountRegistrationFieldMap : ClassMap<AccountRegistrationField>
{
    public AccountRegistrationFieldMap()
    {
        Table("AccountRegistrationField");

        Id(r => r.ID).Column("RegistrationID");
        Map(r => r.AccountID);
        Map(r => r.DefaultValue);
        Map(r => r.IsRequired);
        Map(r => r.Label);
        Map(r => r.Priority);
        References<RegistrationField>(
                 Reveal.Member<AccountRegistrationField>("RegistrationField"))
            .Column("FieldID");

    }
}