I have the following code in Linq to Entity:
var policy= from pol in conn.Policy
where pol.Product.DESCRIPTION=="someProduct"
SELECT pol;
Then, the table Policy, has some dependencies for a table called Entity. If I do this:
foreach(Policy p in policy){
if(!p.Entity.IsLoaded) p.Entity.Load();
IEnumerable<Entity> entities= from ent in p.Entity
Where ent.EntityType.DESCRIPTION=="SomeEntityType"
select ent;
Console.Writeline(entities.ElementAt(0).NAME);
}
It says, "Object not set to an instance", but if I do:
foreach(Policy p in policy){
if(!p.Entity.IsLoaded) p.Entity.Load();
foreach(Entity et in p.Entity)Console.Write(et.NAME);
}
It works!
Can anyone tell me why?
Thank you, Best regards.
I'd say it's because your LINQ statement isn't returning any values, so entities is null.
Your second example works because you're not trying to filter the results.
Do you have some entities that have the DESCRIPTION set to exactly the string (including case)?
Related
I have been trying for hours to get a Distinct to work for my code.
I am using EF 4.3, MVC3, Razor and trying to get a list downto product id and name.
When I run the Sql query against the DB, it's fine.
Sql Query is
SELECT DISTINCT [ProductId]
,[Product_Name]
FROM [dbo].[PRODUCT]
The only other column in that table is a country code so that's why a standard distinct() isn't working.
I have gone as far as creating an IEqualityComparer
Here is code:
public class DistinctProduct : IEqualityComparer<PRODUCT>
{
public bool Equals(PRODUCT x, PRODUCT y)
{
return x.ProductId.Equals(y.ProductId);
}
public int GetHashCode(PRODUCT obj)
{
return obj.ProductId.GetHashCode();
}
}
here is where I called it.
IEqualityComparer<PRODUCT> customComparer = new DistinctProduct();
IEnumerable<PRODUCT> y = db.PRODUCTs.Distinct(customComparer);
But when it hit's that Last line I get an error out of it stating...
LINQ to Entities does not recognize the method 'System.Linq.IQueryable`1[MyService.Models.PRODUCT] Distinct[PRODUCT](System.Linq.IQueryable`1[MyService.Models.PRODUCT], System.Collections.Generic.IEqualityComparer`1[MyService.Models.PRODUCT])' method, and this method cannot be translated into a store expression.
Can anyone tell me what I'm doing wrong?
Thanks,
David
Is there any reason you could just not use a distinct like the following?
var distinctProdcts = (from p in db.PRODUCTs
select new {
ProductId = p.ProductId,
Product_Name = p.ProductName
}).Distinct();
This would remove the country code from the query before you do the distinct.
Entity Framework is trying to translate your query to a SQL query. Obviously it does not know how to translate the IEqualityComparerer. I think the question is whether you want to do the Distinct in the datbase (in which case your client gets only filtered results) or you are OK with bringing all the data to the client and select distinct on the client. If you want the filtering to happen on the database side (which will make your app perform much better) and you want to be able to use different strategies for comparing you can come up with a code that builds distinct criteria on top of your query. If you are fine with bringing your data to the client (note that it can be a lot of data) you should be able just to do (.ToList() will trigger querying the database and materializing results):
IEnumerable<PRODUCT> y = db.PRODUCTs.ToList().Distinct(customComparer);
I'm a total LINQ noob so I guess you'll probably have a good laugh reading this question. I'm learning LINQ to create queries in LightSwitch and what I don't seem to understand is to select an entity based on a value in a lookup table. Say I want to select all employees in a table that have a job title that is picked from a related lookup table. I want the descriptive value in the lookup table for the user to pick from a list to use as a parameter in a query, not the non-descriptive id's.
Can someone point me to an article or tutorial that quickly explains this, or give me a quick answer? I AM reading books and have a Pluralsight account but since this is probably the most extensive knowledge I will need for now a simple tutorial would help me more that watching hours of videos and read thousands of pages of books.
Thanks in advance!
Edit: this is the code. As far as I know this should but won't work (red squigly line under EmployeeTitle, error says that EmployeeContract does not contain a definition for EmployeeTitle even though there is a relationship between the two).
partial void ActiveEngineers_PreprocessQuery(ref IQueryable<Employee> query)
{
query = from Employee e in query
where e.EmployeeContract.EmployeeTitle.Description == "Engineer"
select e;
}
Edit 2: This works! But why this one and not the other?
partial void ActiveContracts_PreprocessQuery(ref IQueryable<EmployeeContract> query)
{
query = from EmployeeContract e in query
where e.EmployeeTitle.Description == "Engineer"
select e;
}
The red squiggly line you've described is likely because each Employee can have 1-to-many EmployeeContracts. Therefore, Employee.EmployeeContracts is actually an IEnumerable<EmployeeContract>, which in turn does not have a "EmployeeTitle" property.
I think what you're looking for might be:
partial void ActiveEngineers_PreprocessQuery(ref IQueryable<Employee> query)
{
query = from Employee e in query
where e.EmployeeContract.Any(x => x.EmployeeTitle.Description == "Engineer")
select e;
}
What this is saying is that at least one of the Employee's EmployeeContracts must have an EmployeeTitle.Description == "Engineer"
Try something like this:
partial void RetrieveCustomer_Execute()
{
Order order = this.DataWorkspace.NorthwindData.Orders_Single
(Orders.SelectedItem.OrderID);
Customer cust = order.Customer;
//Perform some task on the customer entity.
}
(http://msdn.microsoft.com/en-us/library/ff851990.aspx#ReadingData)
Assuming you have navigation properties in place for the foreign key over to the lookup table, it should be something like:
var allMonkies = from employee in context.Employees
where employee.EmployeeTitle.FullTitle == "Code Monkey"
select employee;
If you don't have a navigation property, you can still get the same via 'manual' join:
var allMonkies = from employee in context.Employees
join title in context.EmployeeTitles
on employee.EmployeeTitleID equals title.ID
where title.FullTitle == "Code Monkey"
select employee;
I use Ria Service domainservice for data query.
In My database, there is a table People with firstname, lastname. Then I use EF/RIA services for data processing.
Then I create a Filter ViewModel to capture user inputs, based it the input, I construct a linq Query to access data.
At server side, the default DomainService query for person is:
public IQueryable<Person> GetPerson()
{
return this.Context.Person;
}
At client side, the linq Query for filter is something like(I use Contains function here):
if (!String.IsNullOrEmpty(this.LastName))
q = q.Where(p => (p.LastName.Contains(this.LastName)));
The generated linq query is something like(when debugging,I got it):
MyData.Person[].Where(p => (p.LastName.Contains(value(MyViewModel.PersonFilterVM).LastName) || p.Person.LegalLastName.Contains(value(MyViewModel.PersonFilterVM).LastName)))
When I run the app, I put "Smith" for last name for search, but the result is totally irrelevant with "Smith"!
How to fix it?
I'm guessing here as to what your error is so this might not work for you.
In your 2nd code snippet you do the following.
q = q.Where(p => (p.LastName.Contains(this.LastName)));
This is where I think your error is. Linq does not evaluate the where clause until you iterate over it. Try changing the line to the following.
qWithData = q.Where(p => (p.LastName.Contains(this.LastName))).ToList();
The .ToList() call will load the query with data.
When you check in the debugger, does value(MyViewModel.PersonFilterVM).LastName evaluate to Smith at the time the query is resolved?
Recall that queries are not resolved until they are enumerated.
I think I'm missing something really basic.
var signatures=from person in db.People
where person.Active==true
select new{person.ID, person.Lname, person.Fname};
This linq query works, but I have no idea how to return the results as a public method of a class.
Examples always seem to show returning the whole entity (like IQueryable<People>), but in this case I only want to return a subset as SomeKindOfList<int, string, string>. Since I can't use var, what do I use?
Thanks!
You can get concrete types out of a linq query, but in your case you are constructing anonymous types by using
select new{person.ID, person.Lname, person.Fname};
If instead, you coded a class called "Person", and did this:
select new Person(peson.ID, person.Lname, person.Fname);
Your linq result (signatures) can be of type IEnumerable<Person>, and that is a type that you can return from your function.
Example:
IEnumerable<Person> signatures = from person in db.People
where person.Active==true
select new Person(person.ID, person.Lname, person.Fname);
Why do I get the error:
Unable to create a constant value of type 'Closure type'. Only
primitive types (for instance Int32, String and Guid) are supported in
this context.
When I try to enumerate the following Linq query?
IEnumerable<string> searchList = GetSearchList();
using (HREntities entities = new HREntities())
{
var myList = from person in entities.vSearchPeople
where upperSearchList.All( (person.FirstName + person.LastName) .Contains).ToList();
}
Update:
If I try the following just to try to isolate the problem, I get the same error:
where upperSearchList.All(arg => arg == arg)
So it looks like the problem is with the All method, right? Any suggestions?
It looks like you're trying to do the equivalent of a "WHERE...IN" condition. Check out How to write 'WHERE IN' style queries using LINQ to Entities for an example of how to do that type of query with LINQ to Entities.
Also, I think the error message is particularly unhelpful in this case because .Contains is not followed by parentheses, which causes the compiler to recognize the whole predicate as a lambda expression.
I've spent the last 6 months battling this limitation with EF 3.5 and while I'm not the smartest person in the world, I'm pretty sure I have something useful to offer on this topic.
The SQL generated by growing a 50 mile high tree of "OR style" expressions will result in a poor query execution plan. I'm dealing with a few million rows and the impact is substantial.
There is a little hack I found to do a SQL 'in' that helps if you are just looking for a bunch of entities by id:
private IEnumerable<Entity1> getByIds(IEnumerable<int> ids)
{
string idList = string.Join(",", ids.ToList().ConvertAll<string>(id => id.ToString()).ToArray());
return dbContext.Entity1.Where("it.pkIDColumn IN {" + idList + "}");
}
where pkIDColumn is your primary key id column name of your Entity1 table.
BUT KEEP READING!
This is fine, but it requires that I already have the ids of what I need to find. Sometimes I just want my expressions to reach into other relations and what I do have is criteria for those connected relations.
If I had more time I would try to represent this visually, but I don't so just study this sentence a moment: Consider a schema with a Person, GovernmentId, and GovernmentIdType tables. Andrew Tappert (Person) has two id cards (GovernmentId), one from Oregon (GovernmentIdType) and one from Washington (GovernmentIdType).
Now generate an edmx from it.
Now imagine you want to find all the people having a certain ID value, say 1234567.
This can be accomplished with a single database hit with this:
dbContext context = new dbContext();
string idValue = "1234567";
Expression<Func<Person,bool>> expr =
person => person.GovernmentID.Any(gid => gid.gi_value.Contains(idValue));
IEnumerable<Person> people = context.Person.AsQueryable().Where(expr);
Do you see the subquery here? The generated sql will use 'joins' instead of sub-queries, but the effect is the same. These days SQL server optimizes subqueries into joins under the covers anyway, but anyway...
The key to this working is the .Any inside the expression.
I have found the cause of the error (I am using Framework 4.5). The problem is, that EF a complex type, that is passed in the "Contains"-parameter, can not translate into an SQL query. EF can use in a SQL query only simple types such as int, string...
this.GetAll().Where(p => !assignedFunctions.Contains(p))
GetAll provides a list of objects with a complex type (for example: "Function"). So therefore, I would try here to receive an instance of this complex type in my SQL query, which naturally can not work!
If I can extract from my list, parameters which are suited to my search, I can use:
var idList = assignedFunctions.Select(f => f.FunctionId);
this.GetAll().Where(p => !idList.Contains(p.FunktionId))
Now EF no longer has the complex type "Function" to work, but eg with a simple type (long). And that works fine!
I got this error message when my array object used in the .All function is null
After I initialized the array object, (upperSearchList in your case), the error is gone
The error message was misleading in this case
where upperSearchList.All(arg => person.someproperty.StartsWith(arg)))