Fluent NHibernte Alterations / Conventions

Question

I like the pattern I saw in this blog post (http://marekblotny.blogspot.com/2009/04/conventions-after-rewrite.html), where the author is checking to see if a table name alteration has already been made before applying a convention.

public bool Accept(IClassMap target)
{
    //apply this convention if table wasn't specified with WithTable(..) method
    return string.IsNullOrEmpty(target.TableName);
}

The convention interface I'm using for a string length is IProperty:

public class DefaultStringLengthConvention: IPropertyConvention
{
    public bool Accept(IProperty property) {
        //apply if the string length hasn't been already been specified
        return ??; <------ ??
    }

    public void Apply(IProperty property) {
        property.WithLengthOf(50);
    }
}

I don't see where IProperty exposes anything that tells me if the property has already been set. Is this possible?

TIA, Berryl

Answer 1

To clarify in code what Stuart and Jamie are saying, here's what works:

public class UserMap : IAutoMappingOverride<User>
{
    public void Override(AutoMap<User> mapping) {
        ...
        const int emailStringLength = 30;
        mapping.Map(x => x.Email)
            .WithLengthOf(emailStringLength)                        // actually set it
            .SetAttribute("length", emailStringLength.ToString());  // flag it is set
        ...

    }
}

public class DefaultStringLengthConvention: IPropertyConvention
{
    public bool Accept(IProperty property) {
        return true;
    }

    public void Apply(IProperty property) {
        // only for strings
        if (!property.PropertyType.Equals(typeof(string))) return;

        // only if not already set
        if (property.HasAttribute("length")) return;

        property.WithLengthOf(50);
    }
}

Answer 2

.WithLengthOf() adds an "alteration" (Action<XmlElement>) to the list of alterations to apply when the XML mapping is generated. Unfortunately, that field is private and there is no property to access the alteration list, so I'm afraid there is (currently) no way to check if a property map has had WithLengthOf applied to it.

Answer 3

Until a better alternative comes along, you can use HasAttribute("length").