I have a collection of Employees, and each employee has a collection of Responsibilities. I would like to output a list of the employees sorted by Name and output their Responsibilities, sorted by Title.
So, it should be outputted like this:
Jane Jones
Responsibilities:
Responsibility A
Responsibility B
Mike Smith
Responsibilities:
Responsibility A
Responsibility C
To get the initial collection I use:
var employees = _context.Employees.OrderBy(e => e.Name);
but I can't seem to figure out how to order the Responsibilities subcollection as well.
I'm using MVC and my View receives a strongly typed Employee collection so I don't want to build and return an anonymous type.
You could do something like:
var employees = _context.Employees.OrderBy(e => e.Name);
employees.ToList().ForEach(e => e.Responsibilities = e.Responsibilities.OrderBy(r => r.Name));
1st approach: (is only suitable for LINQ to Objects with Responsibilities defined as IList)
You could copy into a new collection of Employees but this means that you need to re-copy each field into new employee, something like this:
var employees = from e in _context.Employees
orderby e.Name
select new Employee
{
Name = e.Name,
...re-assign other properties...
Responsibilities = e.Responsibilities.OrderBy(r => r.Name).ToList()
};
2nd approach:
Using the DataLoadOptions. Basically, you create a DataLoadOptions object which specifies how to order a particular relationship, so in your case:
var options = new DataLoadOptions();
options.AssociateWith<Employees>(e => e.Responsibilities.OrderBy(r => r.Name));
_context.LoadOptions = options;
var employees = _context.Employees.OrderBy(e => e.Name);
The Responsibilities will be ordered automatically.
Related
I want to change code below to be sql translateable because now i get exception.
Basicallly i want list of customers from certain localisation and there could be more than one customer with the same CustomerNumber so i want to take the one that was most recently added.
In other words - distinct list of customers from localisation where "distinct algorithm" works by taking the most recently added customer if there is conflict.
The code below works only if it is client side. I could move Group By and Select after ToListAsync but i want to avoid taking unnecessary data from database (there is include which includes list that is pretty big for every customer).
var someData = await DbContext.Set<Customer>()
.Where(o => o.Metadata.Localisation == localisation)
.Include(nameof(Customer.SomeLongList))
.GroupBy(x => x.CustomerNumber)
.Select(gr => gr.OrderByDescending(x => x.Metadata.DateAdded).FirstOrDefault())
.ToListAsync();
Short answer:
No way. GroupBy has limitation: after grouping only Key and Aggregation result can be selected. And you are trying to select SomeLongList and full entity Customer.
Best answer:
It can be done by the SQL and ROW_NUMBER Window function but without SomeLongList
Workaround:
It is because it is not effective
var groupingQuery =
from c in DbContext.Set<Customer>()
group c by new { c.CustomerNumber } into g
select new
{
g.Key.CustomerNumber,
DateAdded = g.Max(x => x.DateAdded)
};
var query =
from c in DbContext.Set<Customer>().Include(x => x.SomeLongList)
join g in groupingQuery on new { c.CustomerNumber, c.DateAdded } equals
new { g.CustomerNumber, g.DateAdded }
select c;
var result = await query.ToListAsync();
I am trying to get a list of a database table called oracleTimeCards whose employee id equals to the employeeID in employees list. Here is what I wrote:
LandornetSQLEntities db = new LandornetSQLEntities();
List<OracleEmployee> employees = db.OracleEmployees.Where(e => e.Office.Contains(officeName) && e.IsActive == true).Distinct().ToList();
var oracleTimeCards = db.OracleTimecards.Where(c => employees.Any(e => c.PersonID == e.PersonID)).ToList();
Anyone has any idea?
I'm going to assume you're using Entity Framework here. You can't embed calls to arbitrary LINQ extension methods inside your predicate, since EF might not know how to translate these to SQL.
Assuming you want to find all the timecards for the employees you found in your first query, you have two options. The simplest is to have a navigation property on your Employee class, named let's say TimeCards, that points to a collection of time card records for the given employee. Here's how that would work:
var oracleTimeCards = employees
.SelectMany(e => e.TimeCards)
.ToList();
If you don't want to do this for whatever reason, you can create an array of employee IDs by evaluating your first query, and use this to filter the second:
var empIDs = employees
.Select(e => e.PersonID)
.ToArray();
var oracleTimeCards = db.OracleTimecards
.Where(tc => empIDs.Contains(tc.PersonID))
.ToList();
Using Linq to Entity (Entity Framework) in MVC 3 project.
My model:
Table - Users
UserID (PK)
...
Table - Clients
ClientID (PK)
Table - PropertyItems
PropertyItemID (PK)
Table - MemberContactPreference (Contains PropertyItems selected by Users- many to many)
UserID(FK)
PropertyItemID(FK)
Table ClientProperties (Contains PropertyItems that belong to Clients - many to many)
ClientID (FK)
PropertyItemID (FK)
I want to list all the distinct users that have selected all the properties selected by clients.
My Approach :
I got a list of all properties for a particular client in
Iqueryable<ClientProperty> clientProperties = GetClientProperties(ClientID)
Iqueryable<User> UsersMatchingClientProperties = GetAllUsers();
foreach (ClientProperty property in clientproperties)
{
UsersMatchingClientProperties = (from uem in UsersMatchingClientProperties
join ucp in GetAllMemberContactPreferences on
ucp.UserID == uem.UserID
where uem.MemberContactPreferences.SelectMany(
mcp => mcp.PropertyItemID == property.PropertyItemID)
select uem).Distinct;
}
It gives the right result only first time. As it doesn't reduce the number of items in UsersMatchingClientProperties with each iteration. actually it replaces the collection with new resultset. I want to filter out this collection with each iteration.
Also, any suggestions to do this in Lambda expression without using Linq.
Thanks
That generation of an iqueryable in a for loop seems like a dangerous thing, which could end up in a monster sql join being executed at once.
Anyway, I don't think you need that. How about something like this?
// for a given client, find all users
// that selected ALL properties this client also selected
Iqueryable<ClientProperty> clientProperties = GetClientProperties(ClientID)
Iqueryable<User> allUsers= GetAllUsers();
Iqueryable<MemberContactPreference> allMemberContactProperties = GetAllMemberContactPreferences();
Iqueryable<User> UsersMatchingClientProperties = allUsers
.Where(user => allMemberContactProperties
.Where(membP => membP.UserID==user.UserID)
.All(membP => clientProperties
.Select(clientP => clientP.PropertyID)
.Contains(membP.PropertyID)
)
);
Here is an alternative query in case you want the users that selected ANY property for a given client
// for a given client, find all users
// that selected ANY properties this client also selected
Iqueryable<ClientProperty> clientProperties = GetClientProperties(ClientID)
Iqueryable<User> allUsers= GetAllUsers();
Iqueryable<MemberContactPreference> allMemberContactProperties = GetAllMemberContactPreferences();
Iqueryable<User> UsersMatchingClientProperties = clientproperties
.Join(allMembersContactProperties, // join clientproperties with memberproperties
clientP => clientP.PropertyItemID,
membP => membP.PropertyItemID,
(clientP, membP) => membP)) // after the join, ignore the clientproperties, keeping only memberproperties
.Distinct() // distinct is optional here. but perhaps faster with it?
.Join(allUsers, //join memberproperties with users
membP => membP.UserID,
user => user.UserID,
(membP, user) => user)) // after the join, ignore the member properties, keeping only users
.Distinct();
I trust Hugo did a good job suggesting ways to improve your query (+1). But that does not yet explain the cause of your problem, which is the modified closure pitfall.
I think that after your loop there is some code that actually executes the query in UsersMatchingClientProperties. At that moment the query is executed with the last value of the loop variable property! (The loop variable is the closure in each query delegate that is created in an iteration, and it is modified by each iteration).
Change the loop like this:
foreach (ClientProperty property in clientproperties)
{
var property1 = property;
...
and use property1 in the query. That should solve the cause of the problem. But as said, it looks like the whole process can be improved.
Say I have a Customer entity, and a Sales entity, of 1-to-many relationship.
How could I get all Customers with N number of most recent sales?
var result = Customers.Where(c => c.Sales.Any());
This would return all customers with ALL their sales.
What if I want just 2 sales record from each customer?
P/S: I can do that with query syntax, i'm looking for method syntax solution. I just can't figure out how to chain them together in method syntax form
var result = from cust in context.Customers
select new
{
Customers = cust,
Sales = cust.Sales.OrderBy(s => s.Date).Take(2)
};
This works, but i'm not sure if this is the best way to do it.
EDIT:
OK, it turns out the query syntax that i included here is not working too.
Only the Sales in the anonymous type is effectively reduced to 2 records.
var filtered = result.AsEnumerable().Select(r => r.Customers);
doing this will still result in a list of customers with ALL their sales
You can do a project as described in here
var dbquery = Customers.Select( c => new {
Customer = c,
Sales = c.Sales.OrderBy(s => s.Date)
.Take(2).Select( s => new { s, s.SalesDetails})
});
var customers = dbquery
.AsEnumerable()
.Select(c => c.Customer);
Suppose I have three tables:
Person(pid, ...)
PersonAddress(pid, aid,...)
Address(aid, ...)
Then I want to get the person address like sql:
select a.* from address a join PersonAddress pa on a.addressID=pa.addressID
where pa.personID = myPersonID
Use Entity Framework to create Entity model, then want to write a linq equivalent as above sql.
I tried it in following way:
var addresses = this.GetAddress();
var personaddresses = this.GetPersonAddress();
var query = from ad in addresses
from pa in personaddresses
where ((ad.AddressID == pa.AddressID)&&(pa.PersonID==person.personID))
select ad;
but I got error. Or I try to start from:
var result = this.Context.Address;
var result = result.Join .... //how to write linq in this way?
How to write the linq?
This is untested but if you have all of your relationships setup and you create the model (I have used Model as the name for this) from this you should be able to use the following:
var values = this.Model.Address.Select(a => a.PersonAddress.Where(pa => pa.Id == myPersonID));
You almost never use join in LINQ to Entities.
Try:
var q = from p in Context.People
where p.PersonId == personId
from a in p.Addresses // presumes p.Addresses is 1..*
select a;
Assuming you have three entities: Person, PersonAddress and Address, here is a query that should meet your needs (this example assumes an Entity Framework context named context):
var values = context.PersonAddress.Where(pa => pa.Person.PersonId == myPersonId).Select(pa => pa.Address);
However, if the PersonAddress table exists as a pure many-to-many relationship table (i.e. contains only keys), you'd be better off setting up your Entity Framework model in such a way that the intermediate table isn't necessary, which would leave you with the much simpler:
var values = context.Person.Where(p => p.PersonId == myPersonId).Addresses;
Based on the additional feedback
Because you need to include the country table, you should originate your query from the Address table. In that case:
var values = context.Address.Where(a => a.PersonAddress.Where(pa => pa.Product.Id == myProductId).Count() > 0)
To include the Country table in the result:
var values = context.Address.Include("Country").Where(a => a.PersonAddress.Where(pa => pa.Product.Id == myProductId).Count() > 0)