How to bring name from another context by using foreign key? - entity-framework

Question

I'm tying to write an EntityFramework query to bring hospital name by hospital ID from Hospitals Context to Departments context.I tried couple of things like join tables etc. but I couldn't complete to write that correct query.Here my models and context below
Models
public class Hospital
{
public int Id { get; set; }
public string Name { get; set; }
public string Location { get; set; }
}
public class Department
{
public int Id { get; set; }
public string Name { get; set; }
public int HospitalId { get; set; }
}
Context
public class DataContext : DbContext
{
public DataContext(DbContextOptions<DataContext> options) : base(options) { }
public DbSet<Hospital> Hospitals { get; set; }
public DbSet<Department> Departments { get; set; }
}
Above you can see that model Department has HospitalId to connect Hospital table.After join I want to get that Hospital Name where department belongs to.Result should be department ID,department Name and its Hospital Name .
My Final Try
public async Task<IEnumerable<Department>> GetDepartment(string input)
{
var departmentWithHospital = _context.Departments
.Where(d => d.Hospital.Id == d.HospitalId)
.Include(d => d.Hospital)
.Select(d => new {
departmentId = d.Id,
departmentName = d.Name,
hospitalName = d.Hospital.Name
});
return await departmentWithHospital;
// Compiler Error:doesnt contain a definition for GetAwaiter and no
//accesible extension for GetAwaiter....
}

Answer 1

Three points to note:
1.The await operator suspends evaluation of the enclosing async method until the asynchronous operation represented by its operand completes. like below:
var hospital =await _context.Hospitals.ToListAsync();
return hospital;
2.The relationships between Hospital and Department is one-to-many , you could refer to Relationships to design your model as follows:
public class Hospital
{
public int Id { get; set; }
public string Name { get; set; }
public string Location { get; set; }
}
public class Department
{
public int Id { get; set; }
public string Name { get; set; }
public int HospitalId { get; set; }
public Hospital Hospital { get; set; }
}
3.You want to return a new object list which contains department ID,department Name and its Hospital Name, but your return type of the method is IEnumerable<Department> .So you could directly return a Department collection or define a ViewModel with the properties you want
Return type :IEnumerable<Department>
var departmentWithHospital =await _context.Departments
.Include(d => d.Hospital)
.Where(d => d.HospitalId == hospitalId).ToListAsync();
return departmentWithHospital;
DepartmentWithHospital ViewModel
public class DepartmentWithHospital
{
public int departmentId { get; set; }
public string departmentName { get; set; }
public string hospitalName { get; set; }
}
public async Task<IEnumerable<DepartmentWithHospital>> GetDepartment(int hospitalId)
{
var departmentWithHospital =await _context.Departments
.Include(d => d.Hospital)
.Where(d => d.HospitalId == hospitalId)
.Select(d => new DepartmentWithHospital
{
departmentId = d.Id,
departmentName = d.Name,
hospitalName = d.Hospital.Name
}).ToListAsync();
return departmentWithHospital;
}

Answer 2

You need a Hospital in your Departments class, and a collection of Departments in your Hospital class.
public class Hospital
{
public int Id { get; set; }
public string Name { get; set; }
public string Location { get; set; }
public virtual ICollection<Department> Departments { get; set; }
}
public class Department
{
public int Id { get; set; }
public string Name { get; set; }
public int HospitalId { get; set; }
public Hospital Hospital { get; set; }
}
For the query, try this (Been awhile since I messed with EF, and this is for EF6). I can't remember if you need the include or not, but this should get you an anonymous object with the properties you requested.
This code is not tested.
var departmentWithHospital = context.Departments
.Where(d => d.Hospital.Id == hospitalId)
.Include(d => d.Hospital)
.Select(d => new {
departmentId = d.Id,
departmentName = d.DepartmentName,
hospitalName = d.Hospital.HospitalName
})
.ToList();

Answer 3

If I understood your question correctly, you are looking for this:
var departmentId = "123";
var result = from department in _context.Departments
join hospital in _context.Hospitals
on hospital.Id equals department.HospitalId
where department.Id == departmentId
select new
{
DepartmentID = departmentId,
DepartmentName = department.Name,
HospitalName = hospital.Name
};