Projection.Property returns Property not found

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

Hi,

I have two Classes (User and Line), which are in an n:m relationship. A Line has an Id, so I tried this query to get all the Line-Ids of an user:

Code:

DetachedCriteria lineOfUser = DetachedCriteria.For(typeof(User), "user")
                .CreateCriteria("Line", "userLines")
                .SetProjection(Projections.Property("userLines.Id"))
                .Add(Expression.Eq("user.Id", _CUSTOMER_ID));

lineOfUser.GetExecutableCriteria(session).List();

but this gives me an error:

NHibernate.QueryException: could not resolve property: Id of: NHibernateQueries.Line

So in desperation I did the following: I refactored Line, so that the Id is now called LineId and all over sudden this

Code:

DetachedCriteria lineOfUser = DetachedCriteria.For(typeof(User), "user")
                .CreateCriteria("Line", "userLines")
                .SetProjection(Projections.Property("userLines.LineId"))
                .Add(Expression.Eq("user.Id", _CUSTOMER_ID));

Does work! Interesting why the first doesn't work ...

BTW: I#m using NHibernate 1.2.1.400

wolli · **Posted:** Thu Oct 02, 2008 4:25 am

Can you post the mappings ?

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

OK, these are my mappings:

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping
  xmlns="urn:nhibernate-mapping-2.2"
  assembly="NHibernateQueries"
  namespace="NHibernateQueries"
  default-lazy="true"
  default-access="property">
  
  <class name="User" table="Customer">
    <id name="Id" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property name="Name"/>
    <set name="Line" cascade="all" table="CustomerLine" inverse="false">
      <key column="CustomerId" />
      <many-to-many class="Line" column="FkLineId" />
    </set>
  </class>  
  
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping
  xmlns="urn:nhibernate-mapping-2.2"
  assembly="NHibernateQueries"
  namespace="NHibernateQueries"
  default-lazy="true"
  default-access="property">
  
  <class name="Project" table="Project">
    <id name="Id">
      <generator class="native"/>
    </id>
    <property name="Name"/>
    <set cascade="all" name="Line" table="ProjectLine" inverse="false">
      <key column="ProjectId"/>
      <many-to-many class="Line" column="FkLineId"/>
    </set>
  </class>  
  
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping
  xmlns="urn:nhibernate-mapping-2.2"
  assembly="NHibernateQueries"
  namespace="NHibernateQueries"
  default-lazy="true"
  default-access="property">
  
  <class name="Line" table="Line">
    <id name="Id"  column="Id" type="Int32" unsaved-value="0">
      <generator class="native"/>
    </id>
    <property name="Name"/>
  </class>  
</hibernate-mapping>

wolli · **Posted:** Thu Oct 02, 2008 8:14 am

Hmmm, when you do not name the projection explicitly hibernate creates an alias which in this case probably is "Id". Maybe hibernate gets confused with both the Id then. You can try and use either Projections.Id() or specifiy an explicit name for the projections.

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

wolli wrote:

Hmmm, when you do not name the projection explicitly hibernate creates an alias which in this case probably is "Id". Maybe hibernate gets confused with both the Id then. You can try and use either Projections.Id() or specifiy an explicit name for the projections.

You mean NHibernate get's confused with the Id of the User and the Id of the line?

What do you mean by 'specify an explicit name for the projections'? I already tried:

Code:

.SetProjection(Projections.Property("userLines.Id"))

and Projections.Id() (without trying) shoud give me the Id of the User-object, not the Id of the Line :(

wolli · **Posted:** Thu Oct 02, 2008 8:44 am

.SetProjection(Projections.Property("userLines.Id"),"lineid")

But that's nothing more than a guess. And you're probably right about this:

Quote:

and Projections.Id() (without trying) shoud give me the Id of the User-object, not the Id of the Line :(

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

wolli wrote:

.SetProjection(Projections.Property("userLines.Id"),"lineid")

But that's nothing more than a guess. And you're probably right about this:

Quote:

and Projections.Id() (without trying) shoud give me the Id of the User-object, not the Id of the Line :(

there is no such method

SetProjection(IProjection, string) ... at least Intellisense is complaining about it :

wolli · **Posted:** Thu Oct 02, 2008 9:04 am

Ah, sorry. Seems to be only possible if you use a projection list:

.SetProjection(Projections.ProjectionList().Add(IPrpjection,string))

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

wolli wrote:

Ah, sorry. Seems to be only possible if you use a projection list:

.SetProjection(Projections.ProjectionList().Add(IPrpjection,string))

Cool! That worked - although the query does look a little complicated by now :(

But my first try should work, shouldn't it?

BTW: can you help me with my post at http://forum.hibernate.org/viewtopic.php?t=991143?

wolli · **Posted:** Thu Oct 02, 2008 10:00 am

Quote:

But my first try should work, shouldn't it?

Would have thought that ...

Have you tried using HQL instead. For static queries it's the better approach. You can even put the query to the mapping file (as a named query).

eiben · **Joined:** Tue Dec 04, 2007 4:48 pm **Posts:** 21

wolli wrote:

Have you tried using HQL instead. For static queries it's the better approach. You can even put the query to the mapping file (as a named query).

Nope, I haven't. I just wanted to make sure that I can execute such a query with NHibernate :)

I will have to do some thinking on how/where to create the queries - actually I would like to leave any NHibernate related stuff out of my application layer. But I also don't want to have individual repositories, which have methods like 'GetAllProjectsWithLinesMatchingUser' ... don't know what the best approach would be.

sajith.a · **Joined:** Thu May 27, 2010 11:24 pm **Posts:** 1

i need to get data from releted table also . how can i get that.
like I have table Book and Category
i need to get book details with category name.
how can i get it through "Projection.Property"

Book.MyCategory.Name

if i given like this it shows error

Add(Projections.Property("MyCategory.Name"))

please help me.