Composite key mapping in NHibernate

http://devlicio.us/blogs/anne_epstein/archive/2009/11/20/nhibernate-and-composite-keys.aspx

Create your identifier class...

[Serializable]
public class CategoryProductIdentifier {
        public virtual int ProductId { get; set; }
        public virtual int CategoryId { get; set; }

        public override bool Equals(object obj)
        {
            if (obj == null)
                return false;
            var t = obj as CategoryProductIdentifier;
            if (t == null)
                return false;
            if (ProductId == t.ProductId && CategoryId == t.CategoryId)
                return true;
            return false;
        }
        public override int GetHashCode()
        {
            return (ProductId + "|" + CategoryId).GetHashCode();
        }
}

Update your existing class to make use of the identifier class

public class CategoryProduct
{
        private CategoryProductIdentifier _categoryProductIdentifier = new CategoryProductIdentifier();
        public virtual CategoryProductIdentifier CategoryProductIdentifier
        {
            get { return _categoryProductIdentifier; }
            set { _categoryProductIdentifier = value; }
        }

        private Product _Product;
        public virtual Product Product
        {
            get { return _Product; }
            set { _Product = value;
                _categoryProductIdentifier.ProductId = _Product.Id; }
        }

        private Category _Category;
        public virtual Category Category
        {
            get { return _Category; }
            set { _Category = value;
                _categoryProductIdentifier.CategoryId = _Category.Id; }
        }
        public virtual string CustomizedProductDescription { get; set; }

}

Change your mapping to make use of the new <composite-id> mapping for the key

 
<hibernate-mapping>
<class name="CategoryProduct" table="CategoryProducts">
    <composite-id name="CategoryProductIdentifier" class="CategoryProductIdentifier">
        <key-property name="ProductId" column="ProductID" type="Int32" />
        <key-property name="CategoryId" column="CategoryID" type="Int32" />
        <version name="LastModifiedOn" type="timestamp" column="LastModifiedOn" />
    </composite-id>
    <many-to-one name="Product" column="ProductID" class="Product" insert="false" update="false" access="field.pascalcase-underscore" />
    <many-to-one name="Category" column="CategoryID" class="Category" insert="false" update="false" access="field.pascalcase-underscore" />
    <property name="CustomizedProductDescription" column="CustomizedProductDesc" />
</class>
</hibernate-mapping>

Using NHibernate to format your SQL

Just did this in the immediate window from break point set in Abstract Batcher, GetSQL method in the NHibernate source code

sql.ToString()

"exec [dbo].[GetProjectComments] ?"

SqlClientDriver driver= new SqlClientDriver();

SqlStringFormatter formatter = new SqlStringFormatter(driver);

sql.Visit(formatter)

Expression has been evaluated and has no value

formatter.GetFormattedText()

"exec [dbo].[GetProjectComments] @p0"

Thinking of using this to write a custom little app on the side to make all my SQL look nice again. I know SQL Prompt already does this nicely, but don't have a license for that right now, so this is a nice free alternative I guess.

NHibernate Learning Resources

Apart from the obvious set of videos that everyone knows...

http://summerofnhibernate.com/

I have found this NHibernate documentation site extremely useful also

http://knol.google.com/k/nhibernate-chapter-5-basic-o-r-mapping#Chapter(C2)(A0)5(2E)(C2)(A0)Basic_O(2F)R_Mapping

How to just send the updated columns via NHibernate

Use the following attribute in the top of the mapping file to ensure your update statements are as succinct as possible

Dynamic-update="true"

This will ensure only those column values that have changed actually exist in the SET clause of the UPDATE statement, which is useful if your tables have triggers on them guarded by the TSQL IF UPDATE(MyColumnName) type checks.