I have the following domain set up for persistence with NHibernate: I am using the PaperConfiguration as the root aggregate. I want to select all PaperConfiguration objects for a given Tier and AcademicYearConfiguration. This works really well as per the following example: ICriteria criteria = session.CreateCriteria<PaperConfiguration>() .Add(Restrictions.Eq("AcademicYearConfiguration", configuration)) .CreateCriteria("Paper") .CreateCriteria("Unit") .CreateCriteria("Tier") .Add(Restrictions.Eq("Id", tier.Id)) return criteria.List<PaperConfiguration>(); (Perhaps there is a better way of doing this though). Yet also need to know how many ReferenceMaterials there are for each PaperConfiguration and I would like to get it in the same call. Avoid HQL - I already have an HQL solution for it. I know this is what projections are for and this question suggests an idea but I can't get it to work. I have a PaperConfigurationView that has, instead of IList<ReferenceMaterial> ReferenceMaterials the ReferenceMaterialCount and was thinking along the lines of ICriteria criteria = session.CreateCriteria<PaperConfiguration>() .Add(Restrictions.Eq("AcademicYearConfiguration", configuration)) .CreateCriteria("Paper") .CreateCriteria("Unit") .CreateCriteria("Tier") .Add(Restrictions.Eq("Id", tier.Id)) .SetProjection( Projections.ProjectionList() .Add(Projections.Property("IsSelected"), "IsSelected") .Add(Projections.Property("Paper"), "Paper") // and so on for all relevant properties .Add(Projections.Count("ReferenceMaterials"), "ReferenceMaterialCount") .SetResultTransformer(Transformers.AliasToBean<PaperConfigurationView>()); return criteria.List< PaperConfigurationView >(); unfortunately this does not work. What am I doing wrong? The following simplified query: ICriteria criteria = session.CreateCriteria<PaperConfiguration>() .CreateCriteria("ReferenceMaterials") .SetProjection( Projections.ProjectionList() .Add(Projections.Property("Id"), "Id") .Add(Projections.Count("ReferenceMaterials"), "ReferenceMaterialCount") ).SetResultTransformer(Transformers.AliasToBean<PaperConfigurationView>()); return criteria.List< PaperConfigurationView >(); creates this rather unexpected SQL: SELECT this_.Id as y0_, count(this_.Id) as y1_ FROM Domain.PaperConfiguration this_ inner join Domain.ReferenceMaterial referencem1_ on this_.Id=referencem1_.PaperConfigurationId The above query fails with ADO.NET error as it obviously is not a correct SQL since it is missing a group by or the count being count(referencem1_.Id) rather than (this_.Id). NHibernate mappings: <class name="PaperConfiguration" table="PaperConfiguration"> <id name="Id" type="Int32"> <column name="Id" sql-type="int" not-null="true" unique="true" index="PK_PaperConfiguration"/> <generator class="native" /> </id> <!-- IPersistent --> <version name="VersionLock" /> <!-- IAuditable --> <property name="WhenCreated" type="DateTime" /> <property name="CreatedBy" type="String" length="50" /> <property name="WhenChanged" type="DateTime" /> <property name="ChangedBy" type="String" length="50" /> <property name="IsEmeEnabled" type="boolean" not-null="true" /> <property name="IsSelected" type="boolean" not-null="true" /> <many-to-one name="Paper" column="PaperId" class="Paper" not-null="true" access="field.camelcase"/> <many-to-one name="AcademicYearConfiguration" column="AcademicYearConfigurationId" class="AcademicYearConfiguration" not-null="true" access="field.camelcase"/> <bag name="ReferenceMaterials" generic="true" cascade="delete" lazy="true" inverse="true"> <key column="PaperConfigurationId" not-null="true" /> <one-to-many class="ReferenceMaterial" /> </bag> </class> <class name="ReferenceMaterial" table="ReferenceMaterial"> <id name="Id" type="Int32"> <column name="Id" sql-type="int" not-null="true" unique="true" index="PK_ReferenceMaterial"/> <generator class="native" /> </id> <!-- IPersistent --> <version name="VersionLock" /> <!-- IAuditable --> <property name="WhenCreated" type="DateTime" /> <property name="CreatedBy" type="String" length="50" /> <property name="WhenChanged" type="DateTime" /> <property name="ChangedBy" type="String" length="50" /> <property name="Name" type="String" not-null="true" /> <property name="ContentFile" type="String" not-null="false" /> <property name="Position" type="int" not-null="false" /> <property name="CommentaryName" type="String" not-null="false" /> <property name="CommentarySubjectTask" type="String" not-null="false" /> <property name="CommentaryPointScore" type="String" not-null="false" /> <property name="CommentaryContentFile" type="String" not-null="false" /> <many-to-one name="PaperConfiguration" column="PaperConfigurationId" class="PaperConfiguration" not-null="true"/> </class>