Convert CASE WHEN FROM SQL to NHIBERNATE - nhibernate

Question

I have a SQL statement below that needs to convert it to NHibrnate QueryOver. I have searched the web but can't find a concrete solution. Anyone can help me on this?
SELECT
TABEL1.Id,
CASE WHEN EXISTS (SELECT Id FROM TABLE2 WHERE TABLE2.ID = TABLE1.ID)
THEN 'TRUE'
ELSE 'FALSE'
END AS NewFiled
FROM TABLE1
--Here is the real POCO
public class UserRole
{
[Required]
public virtual User User { get; set; }
[Required]
public virtual Role Role { get; set; }
}
public class UserTenant
{
[Required]
public virtual Tenant Tenant { get; set; }
[Required]
public virtual User User { get; set; }
}
public class Role
{
public int Id {get;set}
[StringLength(255), Required]
public virtual string RoleLabel { get; set; }
[StringLength(4000), Required]
public virtual string RoleDescription { get; set; }
}
public class User
{
public int Id {get;set}
[StringLength(255), Required]
public virtual string Firstname { get; set; }
[StringLength(255), Required]
public virtual string Lastname { get; set; }
}
public class Tenant
{
public int Id {get;set}
[StringLength(255), Required]
public virtual string Name { get; set; }
[StringLength(4000), Required]
public virtual string Description { get; set; }
}
public class AssignRoleUsersModel
{
public virtual int UserId { get; set; }
public virtual string LastName { get; set; }
public virtual string FirstName { get; set; }
public virtual bool IsAssigned { get; set; }
}
--This is the method to get the users assigned or not for that particular role.
public RoleUsers GetRoleUsers(int Id)
{
UserRole userRolesAlias = null;
UserTenant userTenantsAlias = null;
-- This query will get the role depending the Id that have passed. Take note that I don't want to use this query that is why I am converting it to queryOver.
var role = (from r in RoleRepository.Queryable()
where r.Id == Id
select r).FirstOrDefault();
--This query will get all the users having the role result above.Take note that I don't want to use this query that is why I am converting it to queryOver.
var assignedUsers = UserRoleRepository.Queryable().Where(x => x.Role.Id == role.Id).Select(a => a.User.Id).ToArray();
--This is the condition to know if the user was assigned to the role
var projection = Projections.Conditional(Restrictions.Where(() => userRolesAlias.User.Id.IsIn(assignedUsers))
, Projections.Constant(true)
, Projections.Constant(false)
);
var users =
new List<AssignRoleUsersModel>(UnitOfWorkLocalData.CurrentUnitOfWork.Session.QueryOver(() => userTenantsAlias)
.Select(x => x.User.Id)
.Select(x => x.User.LastName)
.Select(x => x.User.FirstName)
.Select(x => x.User.UserName)
.Select(projection)
.TransformUsing(Transformers.AliasToBean<AssignRoleUsersModel>())
.List<AssignRoleUsersModel>());
}

Answer 1

EXTENDED based on the extended question, the way how to do CASE WHEN:
// the ID of searched role, coming as parameter id
int searchedRolId = ...
UserRole userRolesAlias = null;
// this is the SUBQUERY we need, the inner select
var subquery = QueryOver
.Of<UserRole>(() => userRolesAlias)
.Where(() => userRolesAlias.Role.Id == searchedRolId)
.Select(x => userRolesAlias.User.Id);
// here we use NHibernate built in Subqueries tools
var projection = Projections.Conditional(
Subqueries.Exists(subquery.DetachedCriteria) // this is the SUB-SELECT
, Projections.Constant(true)
, Projections.Constant(false)
);
ORIGINAL - This could look like this:
var projection = Projections.Conditional(
NHibernate.Criterion.Expression
.Sql("EXISTS (SELECT Id FROM TABLE2 WHERE TABLE2.ID = {alieas}.ID)")
, Projections.Constant(true)
, Projections.Constant(false)
);
var query = session.QueryOver<Table1>();
ResultDto result = null;
var list = query.SelectList(l => l
.Select(x => x.ID).WithAlias(() => result.ID)
.Select(projection).WithAlias(() => result.DoesExist)
)
.TransformUsing(Transformers.AliasToBean<ResultDto>())
.List<ResultDto>();
The list here contains the set of ResultDtos, with ID and decision if the subtabel TABLE2 record exists. The {alias} will be replaced by NHibernate with the alias of the outert table...
Where this is our DTO for projections:
public class ResultDto
{
public virtual int ID { get; set; }
public virtual bool DoesExist { get; set; }
}