I am using EF Framework to retrieve the data from SQL DB.
Sub Request Table looks like below:
In this table "org_assigneddept" is foreign key to another Department Table.
I have list of Departments as Input and I want to retrieve only those rows from DB whose org_assigneddept is matching the list.
Please find my whole code:-
private List<EventRequestDetailsViewModel> GetSummaryAssignedDeptEventRequests(List<EmpRoleDeptViewModel> vmDept)
{
List<EventRequestDetailsViewModel> vmEventRequestDeptSummary = new List<EventRequestDetailsViewModel>();
RequestBLL getRequestBLL = new RequestBLL();
Guid subRequestStatusId = getRequestBLL.GetRequestStatusId("Open");
using (var ctxGetEventRequestSumm = new STREAM_EMPLOYEEDBEntities())
{
vmEventRequestDeptSummary = (from ers in ctxGetEventRequestSumm.SubRequests
where vmDept.Any(dep=>dep.DeptId == ers.org_assigneddept)
select new EventRequestDetailsViewModel
{
SubRequestId = ers.org_subreqid
}).ToList();
}
}
It is giving the following error at the LINQ Query level:-
System.NotSupportedException: 'Unable to create a constant value of
type 'Application.Business.DLL.EmpRoleDeptViewModel'. Only primitive
types or enumeration types are supported in this context.'
Please let me know as how can I achieve the result
You cannot pass the department VMs to SQL, it doesn't know what those are.
// Extract the IDs from the view models.. Now a list of primitive types..
var departmentIds = vmDept.Select(x => x.DeptId).ToList();
then in your select statement...
..
where departmentIds.Contains(id=> id == ers.org_assigneddept)
..
Related
I have an existing linq query which gets some data into a view model object. This is working fine.
I want to add a new property for data from child table which will have column values from a child table in a comma separated string format.
Problem: I am not able to concatenate the results using string.join
Simplified version of tables showing only relevant fields
part
id
part number
1
ABC1
2
DEF1
vendor
id
vendorname
1
acme
2
john
vendor part name (vendor specific part number)
partid
vendorid
partname
1
1
GDSE-553-32
1
2
JWWVV-HH-01
simplified version of query
result = (from p in DBContext.Parts.Where(w => w.EquipmentId == eId)
select new PartModel
{
Id = p.Id,
Number = p.PartNumber,
VendorPartNames= String.Join(",", DBContext.VendorPartName.Where(w => w.PartId == p.Id).Select(s => s.PartName))//this line causes exception (shown below)
});
Exception:
LINQ to Entities does not recognize the method 'System.String Join(System.String, System.String[])' method, and this method cannot be translated into a store expression.
Please note: the actual query has some joins and other columns, so please dont suggest solutions that requires joins.
If I change the "VendorPartName" to a List type , I can get the results without any problems.
My only problem is in "How to convert the results for "VendorPartName" property to a comma separated strings?"
eg: based on sample table data provided, it should be
GDSE-553-32, JWWVV-HH-01
Entity Framework does not support String.Join() method.
So, what we can do is to fetch VendorPartNames as a string collection and then we can later separate it with ,.
Note: For this, we would first use an anonymous object and later convert it to PartModel.
So your query would look like this:
var parts = DBContext.Parts
.Where(w => w.EquipmentId == eId)
.Select(p => new {
Id = p.Id,
Number = p.PartNumber,
VendorPartNames = p.VendorPartName.Select(n => n.PartName)
}).ToList();
var result = parts.Select(i => new PartModel {
Id = i.Id,
Number = i.Number,
VendorPartNames = String.Join(",", i.VendorPartNames)
}).ToList();
Can anyone explain the behavior I am seeing in the minimal code example below? It seems that for a given field or property, the same two instances of the Entry class are being reused in each iteration of the LINQ to SQL query, even though I use the new operator. The same problem does not show up for LINQ to objects queries. I created a C# console application project using .NET Framework 4 and connecting to a SQL Server 2005 Enterprise database.
public class Set
{
public Entry Field;
public Entry Property { get; set; }
}
public class Entry
{
public int ID;
public string Name { get; set; }
}
class Program
{
static void Main(string[] args)
{
var dc = new DataClasses1DataContext(); // just create a simple dbml with some table from some database
var resultQuery = (
from x in dc.SomeTable
select new Set()
{
Field = new Entry(),
Property = new Entry()
}
);
var sets = resultQuery.ToArray();
Test(sets);
var source = Enumerable.Range(0, 10);
var sourceQuery = (
from x in source
select new Set()
{
Field = new Entry(),
Property = new Entry()
}
);
var sets2 = sourceQuery.ToArray();
Test(sets2);
}
static void Test(Set[] sets)
{
var f = sets[0].Field;
Console.WriteLine(sets.All(x => object.Equals(x.Field, f)));
var p = sets[0].Property;
Console.WriteLine(sets.All(x => object.Equals(x.Property, p)));
Console.Writeline(sets.Length);
Console.WriteLine(object.Equals(f, p));
Console.WriteLine();
}
}
The output of Test() for the LINQ to SQL query is
True
True
1362
False
which indicates that for all of the Set objects produced, all the Field members point to the same single Entry instance and all the Property members point to the same single Entry instance. I.e., the same instance is reused for a respective member in every iteration of the query.
The output of Test() for the LINQ to objects query is
False
False
10
False
which indicates that a new distinct instance is created in each iteration of the query.
Is the LINQ to SQL behavior expected or a bug? Does anyone know if this happens with the Entity Framework?
I don't know if this is a bug or if and why this is expected in LINQ to SQL. I can only answer your last question if that also happens with Entity Framework.
The answer is: No.
With EF you have to use object initializer syntax though when you instantiate the Entry objects. Using the default constructor leads to an exception:
var resultQuery = (
from x in dc.SomeTable
select new Set
{
Field = new Entry { Name = "X" },
Property = new Entry { Name = "X" }
}
);
It doesn't matter how you initialize. Using the code above (and with 4 rows in a small test table) I get this output with your test program:
False
False
4
False
False
False
10
False
It looks that there is a big difference between LINQ to SQL and Entity Framework regarding object materialization during projections.
(I've tested with EF 4.1/DbContext.)
Edit
If I take the modified query in my code snippet above also for your LINQ to SQL query and watch the generated SQL I get the following:
SELECT NULL AS [EMPTY]
FROM [dbo].[SomeTable] AS [t0]
Whereas the same with LINQ to Entites creates this query:
SELECT
1 AS [C1],
N'X' AS [C2],
N'X' AS [C3]
FROM [dbo].[SomeTable] AS [Extent1]
My interpretation is that LINQ to SQL parses the projection code and queries only columns for property values which depend on the "row variable" x. All other properties are filled on the client when the objects get materialized. If an object does not depend on a column value at all, LINQ to SQL creates a single constant object and reuses it in the whole result collection.
In constrast to this Entity Framework also sends constant values (independent of x) to the database server. The values get send back to the client and EF treats those values as if they were column values and updates the properties of the objects in the projection.
This leads also to the big difference that something like this...
Random random = new Random();
var resultQuery = (
from x in dc.SomeTable
select new Set
{
Field = new Entry { ID = random.Next() },
Property = new Entry { Name = "X" }
}
);
...works in LINQ to SQL because apparently the random function value (which is independent of x) is evaluated on the client and then assigned to the property. But EF wants to translate the right side of the property assignment into SQL and send it as SQL fragment to the database server - which fails and leads to the infamous "...cannot translate into store expression..." exception.
Edit 2
BTW: The last code snippet above still creates only a single Field instance in the whole collection: random.Next() is only evaluated once (and also the constructor of Entry is only called once for the Field object). This now is indeed confusing because writing such code one would expect that you want to have a random value for each row returned from the database. It's not the case.
I have a statement:
var items = from e in db.Elements
join a in db.LookUp
on e.ID equals a.ElementID
where e.Something == something
select new Element
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
As you can see, all I need is a collection of Element objects with data from both tables - Elements and LookUp. This works fine. But then I need to know the number of elements selected:
int count = items.Count();
... this call throws System.NotSupportedException:
"The entity or complex type 'Database.Element' cannot be constructed in a LINQ to Entities query."
How am I supposed to select values from multiple tables into one object in Entity Framework? Thanks for any help!
You are not allowed to create an Entity class in your projection, you have to either project to a new class or an anonymous type
select new
{
ID = e.ID,
LookUpID = a.ID
// some other data get populated here as well
};
Your code doesn't work at all. The part you think worked has never been executed. The first time you executed it was when you called Count.
As exception says you cannot construct mapped entity in projection. Projection can be made only to anonymous or non mapped types. Also it is not clear why you even need this. If your class is correctly mapped you should simply call:
var items = from e in db.Elements
where e.Something == something
select e;
If LookupID is mapped property of your Element class it will be filled. If it is not mapped property you will not be able to load it with single query to Element.
I've set up a many-to-many association between two tables based on a third table that just holds a pair of key values. Now I'd like to do a query that groups the right tables key values by the lefts without needing other data.
LeftTable { LeftID, LeftField1, LeftField2 }
JoinTable { LeftID, RightID}
RightTable { RightID, RightField1, RightField2 }
Is there any way to essentially just query the JoinTable and get all the 'RightIDs' grouped by the 'LeftIDs' without the SQL trying to fetch the fields from either side?
The JoinTable is not an entity in its own right in the model, but is mapped to the association.
I've experimented a bit with both using ObjectQuery and EntityCommand (ESQL) and both seem to still load in the other fields by joining to RightTable which I don't need.
My ESQL looks something like:
SELECT lt.LeftID, (SELECT rt.RightID
FROM NAVIGATE(lt, MyModel.LeftToRightAssoc, RightTable) as rt)
FROM MyEntities.LeftTable as lt;
but the generated SQL is still fetching in RightField1 and RightField2.
Surely there must be a simpler way to do this?
Assuming that your class Left has a navigation property Rights (a collection of Right entities) you could try this:
var list = context.Lefts.Select(l => new
{
LeftId = l.LeftId,
RightIds = l.Rights.Select(r => r.RightId)
});
foreach (var item in list)
{
Console.WriteLine("LeftId = {0}", item.LeftId);
foreach (var rightId in item.RightIds)
{
Console.WriteLine("RightId = {0}", rightId);
}
}
You would get a collection of anonymous type objects where each element has the LeftId and a collection of corresponding RightIds. This query should not touch the other fields like RightField1, etc. Instead of an anonymous type you could also create your own custom type and then project into this type in the query above.
I want to limit the length of a column in an EF query, ala:
var query = from ce in entities.ContactEvents
.Include("Person")
.Include("Orders")
where ce.PersonID = personID
orderby ce.DateTimeContact descending
select new ContactEvent
{
ID = ce.ID,
DateTimeContact = ce.DateTimeContact,
Description = ce.Description.Substring(0, 500),
Orders = ce.Orders
};
The query fails because the EF can't project the complex type Orders.
The entity or complex type 'Model.ContactEvent' cannot be constructed in a LINQ to Entities query.
I've tried a few different ways to do the same thing such as use an explicit join in the LINQ expression but so far I always hit a snag populating the Orders collection in the select projection.
Any ideas on how I can construct my query? Ideally I don't even want to use a select projection but I'm assuming I need to in order to be able to limit the length of the description column returned from the database.
You cannot project to entity types. That is the limitation. If you want to return projection (calling select new) you must either return anonymous type or custom non entity type. If you want to return entity type you must always return whole column from linq-to-entities. You can try to trim the column after object is materialized by using:
var data = (from ce in entities.ContactEvents
.Include("Person")
.Include("Orders")
where ce.PersonID = personID
orderby ce.DateTimeContact descending
select ce)
.AsEnumerable()
.Select(e => new ContactEvent
{
ID = e.ID,
DateTimeContact = e.DateTimeContact,
Description = e.Description.Substring(0, 500),
Orders = e.Orders
});