The answer to this question gave rise to this other question: How to use LINQ expressions as static members of classes in queries when the class is related multiple times to a second class
I have an existing ASP.net MVC 4 site which I need to modify.
The core entity within this site are Items that are for sale, which are created by several different companies and divided into several categories. My task is to allow each company its own optional alias for the global categories. Getting the two categories set up in the database and model was no problem, making the application use the new optional alias when it exists and default to the global otherwise is where I'm struggling to find the optimal approach.
Adding a coalesce statement to every LINQ query will clearly work, but there are several dozen locations where this logic would need to exist and it would be preferable to keep this logic in one place for when the inevitable changes come.
The following code is my attempt to store the coalesce in the model, but this causes the "Only initializers, entity members, and entity navigation properties are supported." error to be thrown when the LINQ query is executed. I'm unsure how I could achieve something similar with a different method that is more LINQ friendly.
Model:
public class Item
{
[StringLength(10)]
[Key]
public String ItemId { get; set; }
public String CompanyId { get; set; }
public Int32 CategoryId { get; set; }
[ForeignKey("CategoryId")]
public virtual GlobalCategory GlobalCategory { get; set; }
[ForeignKey("CompanyId, CategoryId")]
public virtual CompanyCategory CompanyCategory { get; set; }
public String PreferredCategoryName
{
get{
return (CompanyCategory.CategoryAlias == null || CompanyCategory.CategoryAlias == "") ? GlobalCategory.CategoryName : CompanyCategory.CategoryAlias;
}
}
}
Controller LINQ examples:
var categories = (from i in db.Items
where i.CompanyId == siteCompanyId
orderby i.PreferredCategoryName
select i.PreferredCategoryName).Distinct();
var itemsInCategory = (from i in db.Items
where i.CompanyId == siteCompanyId
&& i.PreferredCategoryName == categoryName
select i);
For one you are using a compiled function (getPreferredCategoryName) in the query, unless EF knows how to translate that you are in trouble.
Try the following in item definition:
public static Expression<Func<Item,String>> PreferredCategoryName
{
get
{
return i => (i.CompanyCategory.CategoryAlias == null || i.CompanyCategory.CategoryAlias == "") ?
i.GlobalCategory.CategoryName :
i.CompanyCategory.CategoryAlias;
}
}
Which is used as follows:
var categories = db.Items.Where(i => i.CompanyID == siteCompanyId)
.OrderBy(Item.PreferredCategoryName)
.Select(Item.PreferredCategoryName)
.Distinct();
This should work as you have a generically available uncompiled expression tree that EF can then parse.
Related
I have the following class:
public class A {
public B B_a_1 { get; set; }
...
public B B_a_[N] { get; set; }
}
public class C {
public B B_c_1 { get; set; }
...
public B B_c_[M] { get; set; }
}
Class B is mapped to the table via OnModelCreating and has a composite key. But one of the fields in this key is a language code: in some cases it's a current thread language, in other cases all languages need to be selected - for instance, when admin is going to edit localizations (it's a client-created DB for many years and the structure is not going to be changed). This poses the problem of data selection for me. I cannot use Include as-is, because Language code needs to be joined conditionally. Due to large amount of different kinds of B entities (which differ by code - one of key fields) I cannot create a .NET class per each B entity, inheriting it from base class and use HasDiscriminator, HasQueryFilter in base class and stuff like that. In fact, what I now need is to select specific type of B entity by code, using some Extension method like that (pseudo-code is following):
DbSet<A>.Include(x => x.B_a_1).Where(x => x.B_a_1.LanguageCode = "E").Include(x => x.B_a_[N]).Where(x => x.B_a_[N].SomeProperty = "Something")
which would be translated to:
FROM Table_A a
LEFT JOIN Table_B b1 ON b1.Code = a.Code AND b1.LanguageCode = 'E'
LEFT JOIN Table_B b2 ON b2.Code = a.Code AND b2.SomeProperty = 'Something'
I need to 'group' include-where to be able to independently control JOIN conditions per each B-kind entity.
I ended up with the following approach.
Having for instance the class ModuleLanguage with child entity Language, which cannot be explicitly bound via key relationship:
public class ModuleLanguage
{
...
public string LanguageCode { get; set; }
public FixCodeValue Language { get; set; }
...
}
I ignore such property in model creation:
builder.Entity<ModuleLanguage>(b =>
{
b.Ignore(x => x.Language);
}
manual load this property (FixCodeValue class is actually used by many child entities and all of them need to be selected from the same DB table, but based on different criteria):
var currentLanguageCode = DbContext.CurrentLanguage;
await query.ForEachAsync(moduleLanguage =>
{
moduleLanguage.Language = DbContext.FixCodeValues
.FirstOrDefault(language =>
language.DomainId == CentralToolsDomainTypes.CentralTools
&& language.CodeName == CentralToolsFieldTypes.LANGUAGE
&& language.StringValue == moduleLanguage.LanguageCode
&& language.LanguageCode == currentLanguageCode);
});
I'm having a performance issue with lookups using the navigation properties of an EF model.
My model is something like this (conceptually):
public class Company
{
public int ID { get; set; }
public string CompanyName { get; set; }
public EntityCollection<Employee> Employees { get; set; }
}
public class Employee
{
public int CompanyID { get; set; }
public string EmployeeName { get; set; }
public EntityReference<Company> CompanyReference { get; set; }
}
Now let's say I want to get a list of all Companies that have (known) Employees.
Additionally, assume that I've already cached lists of the both the Companies and the Employees through previous calls:
var dbContext = new EmploymentContext();
var allCompanies = dbContext.Companies.ToList();
var allEmployees = dbContext.Employees.ToList();
bool activeCompanies =
allCompanies.Where(company => company.Employees.Any()).ToList();
This (in my environment) generates a new SQL statement for each .Any() call, following the Employees navigation property.
I already have all the records I need in my cached lists, but they're not 'connected' to each other on the client side.
I realize I can add .Include() calls to my initial cache-fill statement. I want to avoid doing this because in my actual environment I have a large number of relations and a large number of lists I'm populating up front. I'm caching largely to keep Linq from generating overly-complicated nested SQL statements that tend to bog down my database server.
I also realize I can modify my query so as to do an in-memory join:
bool activeCompanies = allCompanies.Where
(
company => allEmployees.Any(employee => employee.CompanyID == company.ID)
);
I'm trying to avoid doing such a rewrite, because the actual business logic gets rather involved. Using Linq statements has significantly improved the readability of this logic, and I'd prefer not to lose that if at all possible.
So my question is this: can I connect them together manually somehow, in the way that the Entity Framework would connect them?
I'd like to continue to use the .Any() operator, but I want it to examine only the objects I have in memory in my dbContext - without going back to the database repeatedly.
I have a database base first application so I have no homemade modals as such, just the ones created automatically. I want to display in a single view the one and many parts from a select in single row in an html table/list, here is the SQL that works great in a re-created MS Access Query, - some brackets:
SELECT Facilitiy.FacilityName, Facilitiy.FacilityImage, FacilityDetail.FacilityDetailDescription
FROM FacilityDetail INNER JOIN Facilitiy ON FacilityDetail.FacilityDetailID = Facilitiy.FacilityFK
WHERE FacilityFK = id
And the LINQ that gives me the correct many part of the list:
from fd in db.FacilityDetails
join f in db.Facilities on fd.FacilityID equals f.FacilityFK
where f.B FacilityFK == id
select f
I had kind of hoped that would do it as the SQL does but I need to create a modal that I can put in a view to display:
FacilityImage(one side) | FacilityName(one side) | FacilityDetailDescription(many side)
I have heard I can simply do it by doing something like this???
from fd in db.FacilityDetails.Include("Facilities")
but it seems to make no difference!
Which leads me to believe I need to create a new custom model? If so how would i write it?
I tried something like this but I cant get it to work.
public class FacilitiyDetails
{
public string FacilitiesDescription { get; set; }
public string FacilitiesImage { get; set; }
public string BeachFacilitiesDescription { get; set; }
{
I'm not quite sure what i'm supposed to do here!
Yes you will need a custom model because you're wanting to display multiple types. You'll need to have something like:
public class FacilityModel
{
public Facility Facility { get; set; }
public List<FacilityDetails> FacilityDetails { get; set; }
}
Based on your class above and assuming you have a Facility class already. Then you'll need to change your LINQ to first get the Facility details:
var facility = (from f in db.Facilities
where f.FacilityID == id
select f)
.FirstOrDefault(); //just being safe here,
//if it's null, you'll want to escape out of
//the code below
Then you'll need to get all equivalent FacilityDetails for that facility by doing:
var facilityDetails = (from fd in db.FacilityDetails
where fd.FacilityFK == id
select fd).ToList()
Then you can create a new instance of your Model by doing:
var model = new FacilityModel
{
Facility = facility,
FacilityDetails = facilityDetails
};
How can I load collection with include, I have tried these:
Type.Where(t => t.Entity.Where(e => e.Parent == false).Count() > 0).Include(e => e.Entity)
But the filter is not supported here (Entities recovered not fulfill a condition).
With LinQ To Entities :
var v = from type in ObjectContext.Type
from entity in Type.Entities
where entity.Parent == false
select type;
But type do not contains it's associated Entities.
I can't write select new Type { type.Code, type.Entities } and I can't use anonymous type as it's not adapted for my repository layer.
Have you any ideas on how I can get a list of Type objects with its property Entities satisfying a condition?
Update
Thank you for your response
I think it's not a good idea to use the CTP , no ?
I am sorry, I did not explain my object model, I have :
class Type {
public string Code { get; set; }
public IList<Entity> Entities { get; set; }
...
}
class Entity {
public string Code { get; set; }
...
}
And I want to use your second filtering proposal : Filter both entity sets
Do you have any suggestions without using the CTP ?
Thanks
Rad
as you stated you want to apply filters to the related entities, best to look at the new CTP5 of the EF4 http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx
Look under "Applying filters when explicitly loading related entities"
I'm hoping this will be a rather simple question for anyone who's good at Linq. I'm struggling to come up with the right Linq expression for the following. I'm able to hack something to get the results, but I'm sure there's a proper and simple Linq way to do it, I'm just not good enough at Linq yet...
I have a database accessed through Entity Framework. It has a number of Tasks. Each Task has a collection of TimeSegments. The TimeSegments have Date and Employee properties.
What I want is to be able to get the tasks for a certain employee and a certain month and the timesegments for each task for that same month and employee.
Again, the tasks do not in themselves have month nor date information, but they do by the TimeSegments associated with each task.
Very simplified it looks sort of like this:
public class Model //Simplified representation of the Entity Framework model
{
public List<Task> Tasks { get; set; }
}
public class Task
{
public int Id { get; set; }
public List<TimeSegment> TimeSegments { get; set; }
public Customer Customer { get; set; }
}
public class TimeSegment
{
public int Id { get; set; }
public string Date { get; set; }
public Employee Employee { get; set; }
}
public class Employee
{
public int Id { get; set; }
public string Name { get; set; }
}
So how do I do this as simply as possible with Linq? I.e. tasks and associated timesegments for a certain month and employee. I would also like to be able to get it by Customer BTW...
This is the simplest thing I could come up with:
var tasksWithSegments =
from segment in model.TimeSegments
where segment.Date.Month == month
where segment.Employee.Id == employeeId
group segment by segment.Task into result
select new
{
Task = result.Key,
TimeSegments = result.ToArray()
};
Please note that you might have to add some properties to your model, such as Model.TimeSegment and TimeSegment.Task.
The trick with LINQ queries often is to start at the right collection. In this case the ideal starting point is TimeSegments.
ps. I'm not sure whether Date.Month == month will actually work with EF, but I think it will (with EF 4.0 that is).
Update:
Could you show how to extend this
query and get the tasks for a
particular Customer as well?
I'm not sure what you mean, but you can for instance filter the previous queryable like this:
var tasksWithSegmentsForCustomers =
from taskWithSegments in tasksWithSegments
where taskWithSegments.Task.Customer.Id == customerId
select taskWithSegments;
Can I get the return type to be a list
of Tasks with a list of TimeSegments
if I have this in a method?
Again, not sure what you exactly want, but if you want two separate lists that have no relation, you can do this:
List<Task> tasks = (
from taskWithSegments in tasksWithSegments
select taskWithSegments.Task).ToList();
List<TimeSegments> segments = (
from taskWithSegments in tasksWithSegments
from segment in taskWithSegments.Segments
select segment).ToList();
Of course, if this is what you need, than it might be easier to rewrite the original query to something like this:
List<TimeSegment> segments = (
from segment in model.TimeSegments
where segment.Date.Month == month
where segment.Employee.Id == employeeId
select segment).ToList();
List<Task> allTasks =
segments.Select(s => s.Task).Distinct().ToList();
Once you got the hang of writing LINQ queries, there is no way you want to go back to writing SQL statements or old-fashion foreach statements.
Think LINQ!!!
What I want is to be able to get the
tasks for a certain employee and a
certain month and the timesegments for
each task for that same month and
employee.
This will select tasks from an instance of Model where the task has at least one time segment that in the requested month for the requested employee (untested):
Model model = new Model();
tasks = model.Tasks.Where(t => t.TimeSegments.Any(ts => ts.Employee.Id = requestedId && Convert.ToDate(ts.Date).Month == requestedMonth));