The Linq query "order by" is not working and I've followed all the suggestions found on your site and other sites. Any assistance would be appreciated.
[WebGet]
public IQueryable<vw_providercharge_providers> GetChargeProviders(int submitted)
{
var results = (from p in this.CurrentDataSource.vw_providercharge_providers
where p.submitted == submitted
orderby p.fullname
select p);
return results;
}
Thanks for your input!
Yes, this is a WebGet method for a WCF data service. I get a 400 error if I don't return an IQueryable type, so I modified your suggestion a little. Unfortunately, it still seems to disregard any order-by.
[WebGet]
public IQueryable<vw_providercharge_providers> GetChargeProviders(int submitted)
{
var results = (from p in this.CurrentDataSource.vw_providercharge_providers
where p.submitted == submitted
orderby p.fullname
select p).ToArray();
results.OrderBy(p => p.patientname);
return results;
}
I notice you return an IQueryable<T> - are you calling any LINQ methods on the result before you enumerate it?
Not all LINQ methods preserve order. Most commonly, calling Distinct() after you do the ordering will destroy the order.
Since your method is a marked with a WebGet attribute, I'm assuming that you are calling this method from a Web endpoint, therefore you may need to collapse the collection prior to send it through internet.
Try:
[WebGet]
public vw_providercharge_providers[] GetChargeProviders(int submitted)
{
var results = (from p in this.CurrentDataSource.vw_providercharge_providers
where p.submitted == submitted
orderby p.fullname
select p).ToArray();
return results;
}
This way you have the guarantee that the GetChargeProviders method returns and array instead of an linq expression.
Regards,
I found the cause of the issue.
I had not set the "fullname" column as an Entity Key for the "vw_providercharge_providers" data model entity. Only the identity column was set as an Entity Key. I didn't realize that was a requirement to use it in an order by clause.
Thanks again for your input.
Related
i have the following action method:-
[AcceptVerbs(HttpVerbs.Post)]
public PartialViewResult Search(string q, int classid)
{
var users = r.searchusers(q, classid);
// code does here..............
which calls the following model repository method:-
public IQueryable<User> searchusers(string q, int id)
{
return from u in entities1.Users
where (!u.Users_Classes.Any(c => c.ClassID == id) && (u.UserID.Contains(q))
select u;
}
now if i change the IQueryable to IEnumerable as follow , will there be any changes on how the query will be executed in this case ?:-
public IEnumerable<User> searchusers(string q, int id)
{
return from u in entities1.Users
where (!u.Users_Classes.Any(c => c.ClassID == id) && (u.UserID.Contains(q))
select u;
}
Yes, in my testing once you cast to IEnumerable, that determines the query SQL. Any additional query composition you do after that will be done in memory after the query is executed.
So suppose you have a base query that loads a list of users and returns an IEnumerable. Then before you actually run through that list (thereby executing the query), you also add a .Where(i=>i.username='bob'). In that case, it will execute the whole select, and then apply a LINQ-to-Objects in memory filter for the "where username='bob'" part, which is probably not what you want, instead you want the whole thing to be run as part of the SQL statement.
So yes, always use IQueryable whenever you can so that your fully composed are run at once.
Yes it will change the query, you want to use the IQuerable for anything that uses a remote datasource.
In your case it will force linq to execute the query, where as IQuerable would wait until someone else to execute the query. IQuerable allows them, if they desire, to append more conditions to push down to the database for execution.
I generally enforce IEnumerable at the layer boundary, places where I dont want people modifying the queries that the system is going to generate.
Given the following query:
var query = from item in context.Users // Users if of type TblUser
select new User() // User is the domain class model
{
ID = item.Username,
Username = item.Username
};
How can I re-use the select part of the statement in other queries? I.e.
var query = from item in context.Jobs // Jobs if of type TblJob
select new Job() // Job is the domain class model
{
ID = item.JobId,
User = ReuseAboveSelectStatement(item.User);
};
I tried just using a mapper method:
public User MapUser(TblUser item)
{
return item == null ? null : new User()
{
ID = item.UserId,
Username = item.Username
};
}
With:
var query = from item in context.Users // Users if of type TblUser
select MapUser(item);
But if I do this, then the framework throws an error such as:
LINQ to Entities does not recognize
the method 'MapUser(TblUser)' method,
and this method cannot be translated
into a store expression.
You can't use regular function calls in a query definition like that. LINQ needs expression trees, it can't analyze compiled functions and magically translate that to SQL. Read this for a more elaborate explanation
The techniques used in the cited article are incorporated in linqkit (factoring out predicates) and might be of help, though I'm not sure you can use the same technique for managing projections, which is what you seem to want.
The more fundamental question you should ask yourself here IMHO is whether you really need this extra mapping layer? It seems like you're implementing something that EF is already perfectly capable of doing for you...
Try making your MapUser method static.
I have a table in my model named Customers with a field IsActive. Whenever I run a query on Customers, only the active customers should be retrieved. I can include the filter in every query, but that doesn't look very. I would like to be able to override the Customers property at the Object Context lever, but I am not sure if this is possible. Any help would be very appreciated! Thanks
Although a late response, I will put it here so it can help others.
You can also set a condition for your entity in your edmx file. Select your entity and Goto Mapping Details and create a new condition.
Maybe you could declare new property and use it:
public partial class MyEntities
{
public ObjectQuery<User> ActiveCustomers
{
get
{
return Customers.Where(c => c.IsActive);
}
}
}
I don't know why this is problem for you. You can put one query inside some function:
IEnumerable<Customers> GetActiveCustomers()
{
var activeCustomers =
from cust in db.Customers
where cust.IsActive == true
select cust;
return activeCustomers;
}
And call it every time you like. You can even put active customers in some private List or even better ObservableCollection. Then you can query your result again:
var myCustomers =
from cust in GetActiveCustomers()
where cust.CustomerName == "John"
select cust;
and that's it.
All you need to do is retrieve all of the customers no matter if they are active or not and then use a
foreach(Customer c in Results)
{
if(c.IsActive)
listofactivecustomers.Add(c);
}
I am just getting started with LINQ. I am creating an Entity Framework app that uses the canonical Post and Tag model. A Post contains an ID, Text, and Tags, and a Tag contains an ID, a Name, and Posts.
A previous thread on StackOverflow showed me how to query for a Post that matches all Tag objects (A and B and C) in a search list. But how would I query for a Post that matches any Tag (A or B or C) in the list? Thanks for your help.
Stumbled over the answer right after I posted this question. PredicateBuilder to the rescue!
Here's my code, which uses PredicateBuilder. It is set up as an extension method:
public static IQueryable<Note> WhereContainsAnyTags(this IQueryable<Note> notes, IEnumerable<Tag> searchTags)
{
// Initialize
var predicate = PredicateBuilder.False<Note>();
// Select Notes that contain any search Tags
foreach (var searchTag in searchTags)
{
var tag = searchTag;
predicate = predicate.Or(note => note.Tags.Any(t => t.Id == tag.Id));
}
// Set return value
return notes.AsExpandable().Where(predicate);
}
And here is how I call the code:
searchResults = m_ViewModel.ObjectContext.Notes.WhereContainsAnyTags(m_ViewModel.SearchTags);
Not sure if this would work or not, but worth a try anyway I guess if you are already using WhereIn.
var posts = context.Tags.WhereIn(tag => tag.Name, acceptableValues)
.SelectMany(t => t.Posts);
The WhereIn should give you all the tags that are part of the name, and the SelectMany should give you all the posts containing those tags.
You could aslo do it like this with Entity SQL
var post = ctx.Posts.Where("it.Tags.Id IN (1,2,3)");
I have a lite problem i don't really know how to fix. In my example below i would like to select a list of ProductCategories with ProductItems that are active.
public IEnumerable<ProductCategory> ListProductCategories()
{
return _entities.ProductCategorySet.Include("ProductItems").Where(x => x.ProductItems.Active == true).ToList();
}
The problem is that i can't access productItem property Active in my lambda expression, what is the problem? Do I think totaly wrong when im trying to write a linq query like the one above?
There could be more than one item. You probably want to select the categories where all items are active:
return _entities.ProductCategorySet
.Include("ProductItems")
.Where(x => x.ProductItems.All(item => item.Active))
.ToList();