NHibernate QueryOver where ID is in a list - asp.net-mvc

Question

I have a webpage with criteria fields which filters data. The query for this is:
CompanyAddress ca = null;
CompanyAddress cad = null;
WorkInfo wi = null;
PrivateInfo pi = null;
SearchResultInfo sri = null;
/***************************/
/* SEARCH FOR MAIN COMPANY */
/***************************/
var company = Session.QueryOver<Company>()
.JoinAlias(c => c.Addresses, () => ca)
.Where(() => ca.Main)
.Where(c => c.Status == ContactStatus.Approved)
.Select(
Projections.Property("Id").WithAlias(() => sri.TopId),
Projections.Property("ca.Id").WithAlias(() => sri.Id),
Projections.Property("Name").WithAlias(() => sri.Name),
Projections.Property("ca.Address").WithAlias(() => sri.Address),
Projections.Property("ca.ContactData").WithAlias(() => sri.ContactData),
Projections.Constant(ContactClassType.Company).WithAlias(() => sri.Type)
);
if (!string.IsNullOrEmpty(_name)) company = company.WhereRestrictionOn(c => c.Name).IsLike("%" + _name + "%");
//// TODO: fix error
if (_selectedTag != null) company = company.Where(Restrictions.In("_selectedTag", ca.Tags.Select(x => x.Tag.Id).ToArray()));
if (!string.IsNullOrEmpty(_selectedCity)) company = company.Where(() => ca.Address.City == _selectedCity);
if (_selectedCountry != null) company = company.Where(() => ca.Address.Country.Id == _selectedCountry);
if (!string.IsNullOrEmpty(_selectedZipCode)) company = company.Where(() => ca.Address.ZipCode == _selectedZipCode);
company.TransformUsing(Transformers.AliasToBean<SearchResultInfo>());
Now if selectedTag has an ID the query gives me an error telling ca is null. All the other where clauses work except this one. So I want to check if the incoming ID is in the Tag list from the object CompanyAddress.
Does anyone have an idea whats wrong here?
** SQL FROM ANDREW WITHTAKERS SOLUTION **
SELECT this_.Id as y0_,
ca1_.Id as y1_,
this_.Name as y2_,
ca1_.IdAddressType as y3_,
ca1_.Street as y4_,
ca1_.Number as y5_,
ca1_.ZipCode as y6_,
ca1_.City as y7_,
ca1_.Country as y8_,
ca1_.Email as y9_,
ca1_.Fax as y10_,
ca1_.PhoneNumber as y11_,
ca1_.CellNumber as y12_,
ca1_.Url as y13_,
#p0 as y14_
FROM CON_Company this_ inner join CON_CompanyAddress ca1_ on this_.Id=ca1_.IdCompany
inner join CON_CompanyAddrTag tagalias2_ on ca1_.Id=tagalias2_.IdCompanyAddr
WHERE ca1_.Main = #p1 and this_.Status = #p2 and tagalias2_.Id = #p3',N'#p0 int,#p1 bit,#p2 int,#p3 int',#p0=3,#p1=1,#p2=0,#p3=3

Answer 1

You're going to have to join to Tag in order to do this:
if (_selectedTag != null)
{
Tag tagAlias = null;
company
.JoinAlias(() => ca.Tags, () => tagAlias)
.Where(() => tagAlias.Id == _selectedTag.Id)
}
(Assuming you want Tags compared by Id)
The thing to remember about QueryOver/Criteria is that it's ultimately going to be turned into SQL. calling ca.Tags.Select(...) doesn't make sense from inside of a SQL query since there's an implied JOIN there to Tag.
Also, you're mixing QueryOver and Criteria syntax which is kind of confusing. I'd rework things a bit:
Company companyAlias = null;
var company = Session.QueryOver<Company>(() => companyAlias)
.JoinAlias(c => c.Addresses, () => ca)
.Where(() => ca.Main)
.Where(c => c.Status == ContactStatus.Approved)
.Select(
Projections.Property(() => companyAlias.Id).WithAlias(() => sri.TopId),
Projections.Property(() => ca.Id).WithAlias(() => sri.Id),
Projections.Property(() => companyAlias.Name).WithAlias(() => sri.Name),
Projections.Property(() => ca.Address).WithAlias(() => sri.Address),
Projections.Property(() => ca.ContactData).WithAlias(() => sri.ContactData),
Projections.Constant(ContactClassType.Company).WithAlias(() => sri.Type)
);