I have the following code and would like to know if there is a way to refactor in order to remove duplicated logic.
This results current user with eager loading.
var currentEmployee = RosterContext.Employees
.Where(e => e.User.Id == id)
.Include(e => e.Job.Department).FirstOrDefault();
.
var job = RosterContext.Employees.Where(e=>e.Job.Department.Id == currentEmployee.Job.DepartmentId).ToList();
I created another same context which compares the first line of code to result all employee names who work in same department. My question is, as I am using two linq expression that uses the same context (Employees) am i able to combine both linq queries into one?
It may become a long linq expression but it should serve on getting the current user object followed by comparing user object to get all employees that share the same department id?
It makes sense to try an ORM framework, such as Entity Framework or NHibernate.
ORM framewok will model database FK relationship as a scalar property on one side and vector property (collection) on the other side of the relationship.
For instance Department would have a collection property Jobs, and a Job entity would have a scalar Department property.
DB queries with joins on FK become just dependency property navigation, for example - to access the list of employees in current department you would just return something like employee.Department.Employees - that is, assuming your entities are all loaded (which is rather simple to achieve in EF, using include statement)
In Entity Framework you have the using clause to attach children. So for example in pure EF you could do:
var department = context.Department.Include(d => d.Jobs).First(d => d.DepartmentId == departmentId);
https://msdn.microsoft.com/en-us/library/gg671236%28v=vs.103%29.aspx#Anchor_1
With a repository, you may need to do something like this:
EF Including Other Entities (Generic Repository pattern)
EF Code First supports relationships out of the box. You can either use the conventions or explicitly specify the relationship (for example, if the foreign key property is named something weird). See here for example: https://msdn.microsoft.com/en-us/data/hh134698.aspx
When you've configured your models right, you should be able to access department like so:
var currentUser = _unitOfWork.Employee.GetEmployeeByID(loggedInUser.GetUser(user).Id);
var job = currentUser.Job;
var department = job.Department;
// or
var department = _unitOfWork.Employee.GetEmployeeByID(loggedInUser.GetUser(user).Id).Job.Department;
To show all employees that work in the same department:
var coworkers = department.Jobs.SelectMany(j => j.Employees);
Update
To use eager loading with a single repository class (you shouldn't need multiple repository classes in this instance, and therefore don't need to use Unit of Work):
public class EmployeeRepository {
private readonly MyContext _context = new MyContext(); // Or whatever...
public IList<Employee> GetCoworkers(int userId) {
var currentEmployee = _context.Employees
.Where(e => e.UserId == userId)
.Include(e => e.Job.Department) // Use eager loading; this will fetch Job and Department rows for this user
.FirstOrDefault();
var department = currentEmployee.Job.Department;
var coworkers = department.Jobs.SelectMany(j => j.Employees);
return coworkers;
}
}
And call it like so...
var repo = new EmployeeRepository();
var coworkers = repo.GetCoworkers(loggedInUser.GetUser(user).Id);
You probably would be able to make the repository query more efficient by selecting the job and department of the current user (like I've done) and then the related jobs and employees when coming back the other way. I'll leave that up to you.
Related
Using Entity Framework and LINQ, how might I achieve this TSQL:
SELECT Children.ChildCount, Parent.*
FROM Parent
LEFT JOIN (SELECT ParentID, COUNT(ChildID) AS ChildCount FROM Child GROUP BY ParentID) AS Children
ON Parent.ID = Children.ParentID
Note that this is just a small part of what is already a larger LINQ query that includes other related entities so using a RawSQL query is not an option. Also the Parent table has around 20 columns and I'm hoping not to have to specify each individually to keep the code maintainable.
EDIT: To clarify a couple of things, the model for the output of the query (very simplified) looks something like this:
public class MyEntity
{
public int ID {get; set;}
public string Name {get; set;}
public int ChildCount {get; set;}
// many other properties here including related records
}
So what I'm trying to do is get the ChildCount included in the result of the query so it is included in the EF entity.
You can use a Select Query to project the DB info onto an entity, something like:
var entity = db.Parent.Select(x =>
new MyEntity
{
Id = x.Id,
Name = x.Name,
ChildCount = x.Children
.Select(y => y.ParentId == x.Id)
.Count()
})
.SingleOrDefault(x => x.Id == IDYouNeedToQuery);
}
What this should do is return you 1 instance of your MyEntity class with the Name, ID, and ChildCount properties filled in. Your SQL won't quite match what is generated but this should get you what you want. BTW you can also sub the SingleOrDefault line with a filter of another type, or no filter in which case the entity variable becomes a collection of MyEntity.
For further reading on this technique and how to use AutoMapper to make it super easy to set up, check out this post from Jon P Smith, who literally wrote the book on Entity Framework Core.
Hope this helps.
For anyone who comes across this at a later date, I ended up using AutoMapper as suggested by Nik P (I was already using AutoMapper anyway) to map from db entities to DTOs.
In effect, in my AutoMapper mapping I have:
CreateMap<MyEntity, MyEntityDTO>()
.ForMember(d => d.ChildCount, opt => opt.MapFrom(src => src.ChildEntity.Count()))
Then in my Service layer I call:
IEnumerable<MyEntityDTO> results = await dbContext.MyEntities.ProjectTo<MyEntityDTO>(mapper.ConfigurationProvider).ToListAsync();
Good morning,
I have inherited a database with no foreign key relations and the project is such that i have to ignore this major issue and work around it. Obviously this eliminates some of the cooler features of Entity Framework providing me related entities automatically.
So i have been forced to do something like this:
using (var db = new MyEntities())
{
Entities.Info record = db.Infoes.Where(x => x.UserId == authInfo.User.Id).FirstOrDefault();
//Get all the accounts for the user
List<Entities.AcctSummary> accounts = db.AcctSummaries.Where(x => x.InfoId == record.Id).ToList();
//Loop through each account
foreach (Entities.AcctSummary account in accounts)
{
//pull records for account
List<Entities.Records> records= db.Records.Where(x => x.AcctSummaryId == account.Id).ToList();
}
}
If there a better way to join the "record" and "accounts" Entities, or perhaps a more efficient way for getting "records" in a single query?
TIA
Are you just looking for the .Join() extension method? As an example, joining Infoes and Accounts might look like this:
var accounts = db.Infoes.Join(db.Accounts,
i => i.Id,
a => a.InfoId,
(info, account) => new { info, account });
This would result in accounts being an enumeration of an anonymous type with two properties, one being the Info record and the other being the Account record. The collection would be the full superset of the joined records.
You can of course return something other than new { info, account }, it works just like anything you'd put into a .Select() clause. Whatever you select from these joined tables would be what you have an enumeration of in accounts. You can further join more tables by changing .Join() extensions, returning whatever you want from each.
I want to get all records from a database with #where, then update them. To do this, I have created a query like this:
public async Task MarkAllAsActive()
{
var currentUserId = _userManager.GetCurrentUserId();
await _workOrders.Where(row => row.Status == WorkOrderStatus.Draft).ForEachAsync(row =>
{
row.Status = WorkOrderStatus.Active;
_uow.MarkAsChanged(row, currentUserId);
});
}
But this query selects all fields from the database which isn't good. To solve this I try to select just specific fields like ID, Status:
public async Task MarkAllAsActive()
{
var currentUserId = _userManager.GetCurrentUserId();
await _workOrders.Select(row=>new WorkOrder { Id=row.Id,Status=row.Status}).Where(row => row.Status == WorkOrderStatus.Draft).ForEachAsync(row =>
{
row.Status = WorkOrderStatus.Active;
_uow.MarkAsChanged(row, currentUserId);
});
}
But it return this error:
The entity or complex type 'DataLayer.Context.WorkOrder' cannot be constructed in a LINQ to Entities query.
I've seen a similar post and the same error, but my problem is different because I want to update.
How can I do this?
Sadly you have to fetch the entire entity.
In order to update an entity with EF, the class type edited has to be a DbContext mapped entity .
If you want to Update without fetching Entities to the server , and without writing any SQL you can use Entity Framework Extended Library .
See the update section on the site.
Fetching entity within same entity will not work in your case, as you are getting only selected columns. e.g. You are fetching WorkOrder entity in WorkOrder again.
I would suggest you to use DTO to load selected columns only. It should work. But at the time of update you will have to copy same to db object.
I have an entity Person, which has a related entity Hobby. This is a many to many relationship where a person can have several hobbies, and a hobby can be associated with many people. I want to create a ViewModel that allows new hobbies to be added and/or existing hobbies to be removed from a given Person entity.
The code below works, but I imagine it is rather inefficient.
var newHobbies = new List<Hobby>();
foreach (Hobby hobby in vm.Hobbies)
{
var originalHobby = db.Hobbies.Find(hobby.HobbyID);
newHobbies.Add(originalHobby);
}
originalPerson.Hobbies = newHobbies;
I prefer to do something like this:
var newHobbies = db.Hobbies.Where(x => vm.Hobbies.All(y => x.HobbyID == y.HobbyID)).ToList();
originalPerson.Hobbies = newHobbies;
But I get an error:
Only primitive types or enumeration types are supported in this
context.
How can I update related data without going to the database multiple times?
To avoid that exception you can select first the Ids from the vm.Hobbies collection and after that filter the hobbies you need:
var Ids=vm.Hobbies.Select(x=>x.HobbyID);
var newHobbies = db.Hobbies.Where(x => Ids.Contains(x.HobbyID)).ToList();
// another option could be: db.Hobbies.Where(x => Ids.Any(id=>id==x.HobbyID)).ToList();
originalPerson.Hobbies = newHobbies;
The message says that you can't use vm.Hobbies inside a LINQ-to-Entities query, only primitive types. This is what you can do:
var hobbyIds = vm.Hobbies.Select(h => h.HobbyId).ToList();
var newHobbies = db.Hobbies.Where(x => hobbyIds.Contains(x.HobbyID)).ToList();
The overall construction would be like such:
Your view takes the view model which displays the list of hobbies
You have an action to add a new Hobby passing a Hobby entity back as part of the action
You simply make a call back to the database to create the new association between the Person and Hobby
Add the Hobby entity to the collection in Person
Return passing the view model back to the view
In general EF and MVC are much easier to work with when you try to interact with your entities as whole entities and don't try to micromanage yourself things such as IDs, entity hydration, and so on.
You could join by ID instead of fetching data from the DB:
originalPerson.Hobbies = db.Hobbies.Join(vm.Hobbies, h => h.ID,
v => v.HobbyID, (h, v) => h).ToList();
I have a MembershipGroups table that is associated with a child Members table. The Members table has a Status column which can be set to Active or Inactive.
I want to select all MembershipGroups and only their active Members
As an example,
MembershipGroups
ID----Title
1-----Group #1
2-----Group #2
Members
MembershipGroupID-Name--Status
1-------------------------John----Active
1-------------------------Sally----Inactive
1-------------------------David---Inactive
I'm trying to create a query that looks something like the following (which doesn't currently work):
var query = from mg in db.MembershipGroups
where mg.Members.Status = "Active"
select mg
The result for this example should return a MembershipGroup of ID#1 with only one child Member entity
How can use LINQ-to-SQL to select a parent object that filters on child objects? If I were using straight T-SQL then this would be a simple join with a where clause but it seems to be much more difficult to do using LINQ-to-SQL.
Edit - Updated answer to return the MemberShipGroup object
var query = (from mg in db.MembershipGroups
join m in db.Members.Where(mem => mem.Status == "Active")
on mg.ID equals m.MembershipGroups into members
select new
{
MembershipGroup = mg,
Members = members
}).AsEnumerable()
.Select(m => new MembershipGroup
{
ID = m.MembershipGroup.ID,
Title = m.MembershipGroup.Title,
Members = m.Members
});
In LINQ to SQL, you can use the AssociateWith method on the DataLoadOptions to set your child filter at the context level.
DataLoadOptions opt = new DataLoadOptions();
opt.AssociateWith<Member>(m => m.Status == "Active");
db.LoadOptions = opt;
With this in place, you can simply return your member groups (or filter them for the active ones using where mg.Any(group => group.Members.Status == "Active"). Then when you try to drill into the Members of that group, only the Active ones will be returned due to the LoadOptions.
See also http://msdn.microsoft.com/en-us/library/system.data.linq.dataloadoptions.associatewith.aspx .
One word of warning, once you set the LoadOptions on a context instance, you can not change it. You may want to use a customized context to use this option.
As an alternative, you could use LINQ to SQL's inheritance model to create an ActiveMember type using the Status column as your discriminator and then create an association between the MemberGroups and ActiveMembers types. This would be the approach you would need to use to model this with the Entity Framework if you though about going that route as well as EF doesn't support the concept of the LoadOptions.
Make sure you are including the child objects you are trying to filter on, inside the query.
E.g.
var query = db.MembershipGroups
.Include("Members")
.Where(m => m.Members.Status == "Active");