We have database which does not have proper foreign keys set. We are now generating edmx using this database. What we want is to set navigation property so that we can get corresponding details from other table. Here is example what exactly we are looking for.
Lets say There is a table Employee and Department. Now in database there is no relation between these tables but Employee has DepartmentId which is taken from Department table.
When we fetch Employee we get only DepartmentID but we also want to get Department as property along with it so that we can get information like "DepartMentName", "Location" which is stored in Department table.
We tried adding Navigation property in EDMX file but it fails and keeps giving error related to relation.
Please help
You can go with something like this. Create a wrapper class for Employee and Department.
public class EmpDept
{
public Employee Employee {get; set;}
public Department Department {get; set;}
}
public IEnumberable<EmpDept> GetEmployeesWithDeptpartment()
{
var result = from e in context.Employee
where e.Id == somevalue
select new EmpDept()
{
Employee = e,
Department = context.Department.Where(d => d.Id == e.DepartmentId)
};
return result.ToList();
}
It means you have an extra class, but it's quick and easy to code, easily extensible, reusable and type-safe.
Hope this helps
Related
I am trying to implement Insight.Database in a project, and have run into a brick wall trying to utilize the automatic interface implementation AND mapping object properties to odd column names in the database.
I have the following structure...
class Employee
{
string EmployeeCode {get; set;}
string Name {get; set;}
}
class Vacation
{
int VacationId {get; set;}
DateTime VacationDate {get; set;}
string EmployeeCode {get; set;}
string ApprovedByEmployeeCode {get; set;}
Employee Employee {get; set;}
Employee ApprovedByEmployee {get; set;}
}
My database looks like....
Table: Employees (EmployeeCode, [Name])
Table: Vacations (VacationId, VacationDate, EmployeeCode, ApprovedByEmployeeCode)
View: VacationsView (so I don't have to keep writing [and changing]
the same SELECT over and over)
SELECT v.VacationId, v.VacationDate, v.EmployeeCode, v.ApprovedByEmployeeCode, e1.EmployeeCode AS CreatedByEmployeeCode, e1.[Name] AS CreatedByName, e2.EmployeeCode AS ApprovingEmployeeCode, e2.[Name] AS ApprovingName
FROM Vacations v
INNER JOIN Employees e1 ON v.EmployeeCode = e1.EmployeeCode
INNER JOIN Employees e2 ON v.ApprovedByEmployeeCode = e2.EmployeeCode
Stored Procedure: GetAllVacations
SELECT * FROM VacationsView
Finally, with Insight.Database, I am trying to have an interface that will autopopulate my objects and tell it how to use the different column names from my stored procedure for the "employee" properties.
public interface IMyRepository
{
IList<Vacation> GetAllVacations();
}
....
var repo = conn.As<IMyRepository>();
return repo.GetAllVacations();
This works (as in doesn't error) and all the properties of my vacation are correctly mapped, but my two "employee" properties are null (as expected because the column names don't line up to the property names of an employee object). What I can't figure out is how to tell Insight "Use CreatedBy.." fields to build the "Employee" property and "Approving..." fields to build the "ApprovedByEmployee" property.
I have been able to accomplish it using OneToOne with a callback and columnOverride and then use a standard Query(). I.E..
var vacationStructure =
new OneToOne<Vacation, Employee, Employee>(
callback: (vacation, createdBy, approvedBy) =>
{
vacation.Employee = createdBy;
vacation.ApprovedByEmployee = approvedBy;
}, columnOverride: new ColumnOverride[]
{
new ColumnOverride<EmployeeModel>("CreatedByEmployeeCode", "EmployeeCode"),
new ColumnOverride<EmployeeModel>("CreatedByName", "Name"),
new ColumnOverride<EmployeeModel>("ApprovingEmployeeCode", "EmployeeCode"),
new ColumnOverride<EmployeeModel>("ApprovingName", "Name")
});
....
var results = await conn.QueryAsync("GetAllVacations", new {employeeCode}, Query.Returns(_vacationStructure));
However, I'm really trying to utilize the auto interface capabilities of Insight.
Is what I'm trying to do possible?
Assembling repeated child objects isn't something that's currently done automatically, and the interface implementation doesn't give you the right hooks to override the behavior.
Some options:
A. Change the shape of your result set to return the employees as a list with properties.
B. If the classes aren't sealed, derive from Employee so Insight can differentiate between the classes:
public class AssigningEmployee : Employee {
public string AssigningName { get { return Name; } set { Name = Value; } }
...
}
These solutions are all meh. The whole point of Insight.Database is to just work without a lot of extra work. So...
I opened a github issue to track this:
https://github.com/jonwagner/Insight.Database/issues/384
I've been doing some research on this topic and figure out a way to achieve this queries in my project but I'm not sure if something here is wrong. please help.
in summary I've created the entities like this:
class Student
{
public int StudentId { get; set; }
public string Name { get; set; }
public ICollection<Courses> Courses {get;set;} //or public List <Courses> {get;set;}
}
class Course
{
public int CourseId { get; set; }
public string Name { get; set; }
public ICollection<Students> Students {get;set;} //or public List<Students> {get;set;}
}
// We can see here that the database creates the Join Table Correctly
What I want to do:
Display in a grid view each student and for each of the students display the courses in wich they are enrolled.
If I made a simple query like
dbContex.Students.ToList();
and we look at the list the Collection of courses value is null. What is happening here?, shoulden't EF map this and make a query to SQL to get the info?
After this y could not solve the problem because the info that I found was using other approach of the framework (Diagram First ,i think) and they set up things in the entities diagram.
How did I work out the problem :
Find out in a Wordpress Post a Query that I haven´t tried out and add some other lines of code to achieve what I wanted:
aux_S = contexto.Students.ToList();
foreach(var element in aux_S)
{
element.Courses= contexto.Courses.Where(c => c.Students.Any(s => s.StudentId == element.StudentId)).ToList();
}
// I know I can make a projection to dismiss all the fields that I do not need , this is just to try it out
Am I wrong doing this ?
It worked, but how is it possible?
One of the slower parts of a database query is the transfer of the data to your machine. So it is good practice to transfer only the data you plan to use.
When you use LINQ in entity framework, using Queryable.Select is a good way to specify exactly what data you want to transfer. This is usually done just before your final ToList / ToDictionary / FirstOrDefault / Single / ...
You want all Students, each with all his Courses. If you look at your tables, you'll see that there is more data in the tables then you want. For instance, each Student has an Id, each of his Courses have the same value for StudentId. So if a Student attends 20 Courses, you would have transferred the same value for StudentId 21 times.
So to make your query efficient: Select only the Properties of Students you plan to use, with only the Properties of the Courses of these Students you are interested in.
This will automatically solve your problem:
var result = myDbcontext.Students
// if you don't want all Students, use a Where:
.Where(student => student.City = "Guadalajara")
// Select only the properties you plan to use:
.Select(student => new
{
Id = student.Id,
Name = student.Name,
Birthday = student.Birthday,
Address = new
{
Street = student.Street,
City = student.City,
...
}
Courses = student.Courses
// if you don't want all courses: use a where
.Where(course => course.Start.Year == 2018)
// again: select only the properties you plan to use
{
Name = course.Name,
Location = course.Location,
...
// One of the useless properties to transfer:
// StudentId = course.StudentId
})
.ToList();
});
If you perform this query:
var studentslist = dbContex.Students.ToList();
Each item on studentslist will have the 'Courses' collection null, because, although the connection/relation exists (between each table), you didn't specify that you wanted that collection populated. For that to happen you can change your query accordingly:
var studentslist = dbContex.Students.Include(p => p.Courses).ToList();
Now, after running the last query, if you get an empty list on one/any of the items, then it means those items (students), aren't linked to any courses.
You are not lazy loading, if you add virtual like: public virtual ICollection<Courses> Courses {get;set;} you should get the courses loaded.
However, I'd advise using lazy loading since it may cause performance issues down the road, what you want to do is eager loading.
So when you are querying your student you would simply do this:
dbContex.Students.Include(c => c.Courses).ToList();
I am having class employee which contain complex property Department.
public Class Employee
{
public int Id { get; set;}
public Department {get; set;}
}
public Class Department
{
public int Id {get;set;}
public string Name { get;set;}
}
i create the map for both
(consider the above both class are available in two namespace 'source', 'destination')
Mapper.CreateMap<source.Employee,destination.Employee>()
Mapper.CreateMap<source.Department,destination.Department>()
when i project it.
empQueryable.Project().To<destination.Employee>();
If i saw the NHProfiler
I found that it loads the entity Department
and create the query
select ... from employee left outer join Department .....
i don't know why it loads entity Department, it should make just the projection.
I'm going to go out on a limb here and assume that "destination.Employee" contains references to the "destination.Department". When AutoMapper builds a projection, it does the same as it would as "Mapper.Map". It crawls the destination type, its properties, and its member's properties all the way down. In short, it will build a Select expression something like:
.Select(e => new destination.Employee {
Id = e.Id,
Department = new destination.Department {
Id = e.Department.Id,
Name = e.Department.Name
}
});
You have a few choices here:
Ignore members you don't want mapped in your employee configuration, namely the "Department" property
Create targeted destination types based on use case, and don't share destination types that require different hydrated data based on different needs.
Use explicit expansion (ForMember(d => d.Department, opt => opt.ExplicitExpansion()), then explicitly expand that member in your projection as needed, with the overload for "Project.To" that takes a list of members to expand.
Currently I am new to MVC and practicing with some demo applications.
I have 2 models.
Employee - (with data members employeeId,name,gender,city,deptId)
Department - (with data members id,name,Collection employees )
I have put these two classes inside a context class inheriting from DbContext.
Problem is when I try to get employee data based on deptId , it throws error that department_Id column is not defined. If I remove the employees data member from Department then everything works fine. What exactly is happening here, why is it automatically adding a column, and how to tackle it?
Don't add deptId property to your Employee class. Just add a navigation property like this:
public virtual Department Department { get; set; }
And your Department class:
public virtual ICollection<Employee> Employees { get; set; }
Then Entity Framework will create all necessary relationships automatically for you.
For more informatin about Navigation Properties take a look at here: http://msdn.microsoft.com/en-us/data/jj713564.aspx
Say I have 3 tables, Cars, Persons, CarOwners.
Cars is just a table of cars and Persons are different people that can own cars. CarOwners has a CarId and a PersonId relationship and a CarOwnerId PK.
If I just create the relationship and then drag them to the linq context, a property of the Person class will be generated called CarOwners. To get the cars that this person owns I would have to do the following query:
var cars = person.CarOwners.Select(c=> c.Car);
But I would like to be able to do:
var cars = person.Cars;
Is that at all possible? The extra step is quite annoying.
You can just create a new property on Person:
public partial class Person
{
public IEnumerable<Car> Cars
{
get { return this.CarOwners.Select(c => c.Car); }
}
}
Or upgrade to Entity Framework where you can separate logical model from physical model.
Try to remove the CarOwnerId from CarOwners in your sql database. Then select CarId and PersonId in designer mode in SSMS (using shift key), right click and select `Set Primary Key.
In EF 4, you'll get only navigation keys in your model this way (you can use: Person.Cars and Car.Persons). Not sure about L2S.