NHibernate: Unrecognised method call:Boolean Contains(Int64)

A colleague asked me for help with a complex NHibernate query. He had written a query using the NHibernate Linq support but when he tried to execute the query, NHibernate complained with the following error message:

‘'Unrecognised method call: System.Int64:Boolean Contains(Int64)”

Let’s have a look at his query first:

	_session.Query<Product>()
	.Where(p => shoppingBasket.Products.Contains(p.ProductId))
	.Select(p=> p);

view raw failingcontainsquery.cs hosted with ❤ by GitHub

It seems that NHibernate cannot translate the Contains() call in a related NHibernate query. To fix this, we switched from the Linq syntax to the QueryOver syntax:

	var productIds=shoppingBasket
	.Products
	.Select(p=> p.ProductId)
	.ToArray();
	_session.QueryOver<Product>()
	.WhereRestrictionOn(p => p.ProductId)
	.IsIn(productIds)
	.Select(p => p);

view raw succesfulcontainsquery hosted with ❤ by GitHub