.net - Working With The ObjectQuery Single Enumeration Challenge In Linq-To-Entities Entity SQL?

Dec 30, 2011

I'm working on modifying this example:

Using advWorksContext As New AdventureWorksEntities
' Call the constructor that takes a command string and ObjectContext.
Dim productQuery1 As New ObjectQuery(Of Product)("Product", advWorksContext)

[code]....

An ObjectQuery can be enumberated only once. (Subsequent attempts at enumeration throw an exception.) The enumberation takes place in the for each statement. The problem is that if the query is empty attempting a For Each will throw an exception. But if I check for a count:If productQuery1.Count > 0 Then . . .

That eats up my one chance at enumeration. I could nest the For Each in a try/catch block and throw away the empty query exceptions, but that's ugly.

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Linq To Entities Filtering An Entity Dynamic/Strongly Typed?

Apr 24, 2009

I am binding a Winforms Grid to an entity. (For reasons I won't go into here it must be bound to the entity, not the result a query) The code is as follows:

grid.DataSource = myEntities.entityName.Where("it.field = " & field)

It works, but it obviously isn't strongly typed. Is there a way to define the Where clause of an entity using a strongly typed notation?

Update One Entity Based On Results Of Another LINQ-to-Entities Query

Apr 9, 2011

I have the following LINQ-to-Entities query:[code]This will give me all the resident assignments for the current year/term. Then I have this LINQ-to-Entities query:[code]This will give me all the rooms. I want to iterate through the assignments and based on what room is assigned update the occupancy in reset_occupancy. I'm not 100% sure how to accomplish this. Here is my pseudo code of what I want to accomplish:[code]

Update One Entity Based On Results Of Another LINQ-to-Entities Query?

Dec 15, 2009

I have the following LINQ-to-Entities query:

' Get all the residency assignments that match the term/year.
Dim assignments = From p In dbContext.Residents _
Where p.semester = term _

[code].....

.net - Entity Framework 4.1 Code First+MVC3 And Accessing Entities Of A Certain Type?

May 13, 2011

I am using Entity Framework 4.1 code first+MVC3 and the inheritence stratagy that I use is TPC

I have the following classes
Public Class ObjectBase
<Key()>
Public Property Id As Integer
Public Property Description As String
End Class

[Code]...

Question 1 (and question 2) should be very simple, but I have allready spent hours on Google to find an answer with no result at all. The only thing I have found is that you can get all computers in ObjectBase by writing context.ObjectBase.OfType(Of Computer), and that does not help since you cannot write context.BorrowObjects.ObjectBase.OfType(Of Computer) code samples in VB.NET (if you can), but more importantly: Please ensure that the codesamples you supply work without hours of modification!

Asp.net - Linq Group By An Entity And Then Order By The Grouped (nullable) Entity

Jul 27, 2011

I am trying to build a survey engine from an existing database design which is like this.

[Code]...

The line Order By Key.RecordOrder throws a null reference exception and I can understand why. Can someone advise on how to resolve this by just modifying this one query? I am fairly new to LINQ and the necessity to write this project

[Code]...

Linq To Entities. GetPropety(name).GetValue Not Recognised By Linq?

Apr 20, 2011

I have a listbox on my xaml form that I bound to a List(Of MyType) property. I populated this list like so:

Dim fields As List(Of CheckableFields) = New List(Of CheckableFields)
Using context As ITIPEntities = New ITIPEntities()
Try[code]....

Now I'm at the point where the user selects the fields they want included in a report and I need to iterate over the required fields. This is my linq query:

For Each checkedField In _requiredFields
If checkedField.IsChecked Then
If checkedField.FieldData IsNot Nothing AndAlso checkedField.FieldData.Trim IsNot String.Empty Then[code].....

.net - Linq Expressions With Linq To Entities?

Feb 28, 2012

The pattern I'm trying to avoid is checking if a string (normally a control's text value) is null/empty, and if it is, comparing it using Contains to a field in my data. Obviously the field isn't hard-coded into my extension, neither is the object type.What I've got works perfectly in Linq to Objects, but I get the generic run-time error "LINQ to Entities does not recognize the method 'System.String Invoke(GenericQueryHelper.Customer)' method, and this method cannot be translated into a store expression." when using an entity framework model.

Here's what I have:

<System.Runtime.CompilerServices.Extension()>
Public Function CompareAndFilter(Of T)(source As System.Linq.IQueryable(Of T), expressionField As System.Linq.Expressions.Expression(Of System.Func(Of T, String)), compareTo As String)

[code]....

I want my usage to look something like this:

Dim results = repository.Customers.CompareAndFilter(Function(c) c.FirstName, searchText)

I do need to get this running against a SQL database really, as it is filtering results, so I don't want to be doing that in memory.

Asp.net - Method For Attaching A Single Key/value Pair Attribute To An Enumeration?

May 4, 2012

I'm trying to figure out what the best method is for attaching a single key/value pair attribute to an enumeration where the key is my MerchantId and the value is the corresponding TransactionKey. What I currently do is put a comma delimited string into a StringValueAttribute class:

Public Enum Merchants
<StringValue("coke,faj80785hq+faf=-1=-jfa+">
Coke = 0
<StringValue("pepsi,adfji=-901jnas++fdj98ua")>
Pepsi = 1
<StringValue("drpepper,jk878-=+9kdkdja0=a=f--daj")>
DrPepper = 2

[Code]...

Is this the most efficient way to do this? Instead of StringValueAttribute, what about creating an attribute using a Dictionary(Of String, String) since it is a key/value pair list? Or String Array or List? Maybe something in LINQ?

Inner Join In Linq To Entities?

Apr 23, 2009

Given two tables, customer and orders, how would one do a linq query to entities to find any customers with open invoices started before a certain date?

Asp.net - Concatenating String In LINQ-to-Entities?

Apr 7, 2011

This code works if I take out

" " + p.MIDDLE_NAME

Thus the remaining code looks like:

p.FIRST_NAME + " " + p.LAST_NAME

Maybe LINQ-to-Entities just doesn't support concatenating more than two strings at a time?

Protected Sub btnFilter_Click(sender As Object, e As EventArgs) Handles btnFilter.Click
Dim dbContext As Campus6Entities = New Campus6Entities

[Code]....

Databind To A Treeview Using Linq To Entities?

Feb 12, 2010

I have seen other similar questions dealing with WPF Almost exactly the same but I can;tfigure this out in ASP.net. I have a Pages table with a parentpage foreign key and want to databind them to a treeview. In the past I have created a hierarchicaldataset from a dataset but would like to stay within the entities framework if I can

EF4: LINQ 2 Entities Query Works In C# But Not In VB

Dec 11, 2010

the query below throws a System.NotSupportedException: "Unable to cast the type 'System.Linq.IOrderedQueryable1' to type 'System.Linq.IQueryable1'. LINQ to Entities only supports casting Entity Data Model primitive types." The exception is only raised in the VB.Net version. When translated to C#, no exception is raised.

Dim doesThisCrash = From outerOrder In orders
Where outerOrder.ProductId =
(From p In products Join o In orders On p.Id Equals o.ProductId

[Code]....

Get CurrentTime From SQL Server With LINQ/Entities?

Sep 14, 2011

I am using LINQ with Entity Framework, and I need to get the SQL server timeCan anyone tell me how can I create a method so it retrieves the current server time?

VS 2008 Linq 2 Entities Can't Add An Association

Mar 21, 2009

I'm a bit of a n0ob to all this and I'm having trouble finding good resources on the net.What I'm trying to do is define a one-to-many relationship between two entities. I'm using the GUI tool in Visual Studio - and have created the tables in Microsoft SQL Server Management Studio.Basically, I have two tables....a 'Users' table and a 'Sites' table. A single user can have many sites associated with it.Users has a primary key of 'UID' and the Sites table as a primary key of 'Site_ID'.Sites also has a column 'UID' that should indicate which user that site is associated with.Anyway - it sounded pretty simple; but no matter what I attempt to do, I can't seem to get it to work. Mostly, I get validation errors - sometimes run-time errors, or sometimes, no actual data even though there should sites that match the UID of the user.I am able to connect and write LINQ against my Users table/pull down User objects - but can't seem to get it to know that the Sites are associated with the user.In the GUI - if I go to 'Add Association' and create a 1 to many link between Accounts and Sites - and Validate - I get an error saying, "Error1Error 11008: Association 'AccountsSites' is not mapped."

It seems like, when I try to make an association, it wants to link the 'Keys' of each entity.But U_ID and SITE_ID are the keys and, obviously, shouldn't match.If I click on the line it created in the GUI and I go to 'Table Mapping' I can see that it is trying to match those keys. Since I want it to match user_ids my first thought is to just make the U_ID the entity Key in the Sites entity but, of course, that's wrong because it would no longer allow a 1 to many relationship.

Linq To Entities Query With Child Objects?

Oct 13, 2011

Basically I have the follwing:Dim ctx As New AdminCoreEntities Dim roles = (From r In ctx.Roles where r.Name.StartsWith("cust") Select r) 'list of System .Linq.IQueryable(Of AdminCoreModel.Role)

[code]...

The error i get when i run this is: Unable to cast object of type System.Data.Objects.ObjectQuery`1[AdminCoreModel.Role] to type AdminCoreModel.Role

Basically I have a many to many situation and I try to get all the Quicklinks objects queried by their roles and not quite sure why EF will cast to a single AdminCoreModel.Role when i.Roles is a collections of objects.

Linq To Entities, Filter Using Where And A List Of Stings?

Nov 2, 2011

I am trying to write a query for an existing database, I am using LINQ on EF3.5 inside VS2008 as that is the only environment available to me.I have a starter query that gives me a list of items so the user can select what they want.

"e.Result =
From c In MLDb.TBL_FeatureInfoSet
Order By c.INSP_ROUTINE_NM
Select c.INSP_ROUTINE_NM
Distinct"

The user can then select from the list one or several items they are intersted in and i want to use these as the filter in a further database call. It's not then difficult to have a where to filter on one string however, I would also like to be able to allow the user to select several items from the list box and the data for all of those to be returned.

[Code]...

Update An Object's Foreign Key Value With LINQ To Entities

May 4, 2012

[code]How do I update the ProdServiceID in the database using LINQ to entities?

LINQ To XML. Enumeration Yielded No Results?

Oct 17, 2009

I'm having trouble populating an object from an XML file. I've copied an example I've found almost exactly, with variable names changed, but I keep getting the "Enumeration yielded no results" exception.

Here is my code:

[code]...

Essentially, the XML query is supposed to return the title and the description for every Property which has an element called Language Code, which is equal to "en-us". I have a feeling that my problem lies in my XML code, but I've been stuck here for a long time now.

.net - Detect Empty Results In A Linq-To-Entities Query?

May 29, 2009

The only way I know of is awkward:

'check for empty return
Dim count As Integer = (From s In myEntity.employee Where employeeID = myEmployeeIDVariable).Count
'If there is a record, then process

[code]....

.net - In Linq To Entities - How To Do An Inner EXISTS (SELECT 1 FROM - Type Of Query

Mar 6, 2011

I am trying to write a LINQ equivalent of

SELECT C1, C2, C3
FROM T1
WHERE T1.C4='xyz' AND
EXISTS (SELECT 1 FROM T2
WHERE T1.C17 = T2.C24)
ORDER BY C3

I'm using EF CTP 5, so I have a DBContext variable named dbc, which includes DBSet objects T1s and T2s, based on POCOs T1 and T2.

In LINQ I write

DIM IND = From i In dbc.T1s
Where i.C4 = "xyz"
And (From t In dbc.T2s Where i.C17 = t.C24).Any
Select i.C1, i.C2, i.C3
Order By C3

Running the query I get the error message "Unable to create a constant value of type 'T2'. Only primitive types ('such as Int32, String, and Guid') are supported in this context." When I omit the inner expression (third line in the LINQ code), the query runs fine. I tried switching the orders of the inner comparison, to be t.C24 = i.C17, with no effect.

Asp.net - LINQ To Entities Does Not Recognize The Method System.ObjectCompareObjectEqual

Mar 21, 2012

I had a code segment on an asp.net page in the code-behind file. I decided to move it into a public subroutine in a module (general_functions.vb). Once I did this, however, the code no longer works - it throws an error. On the original code-behind I replaced the original code with a call like so:

[Code]...

LINQ To Entities .Any() Results In Null Reference Exception?

Nov 16, 2011

I have a simple query as below:

Dim sizings = From a In db.Sizings
Where a.Customer.ID = customer.ID
Select a
If sizings.Any Then
.....

The sizings.Any line is throwing a null reference exception. I thought I was meant to use .Any to determine if there were any rows returned?isnothing(sizings) returns false.

Edit - Resolution:Don't use null objects in the LINQ Query!

Use Linq To Entities To Group A Collection Without Using Anonymous Types?

Apr 24, 2012

The documentation has an example about grouping on multiple properties[code]...

Is it possible to rewrite the original query to just return IEnumerable(Of CustomerRegionGroup), or do I have to use the anonymous type, and run a second query on the result of the first?

VS 2010 Use LINQ To Entities To Populate List View

Jun 23, 2011

Here's what I tried, but I get an error at run time on the AddRange line that states "Only parameterless constructors and initializers are supported in LINQ to Entities."

[Code]...

Obtaining Name/value Pair Of Enumeration With LINQ [VB 2010]?

Jul 23, 2009

I'm trying to obtain name/value pair of enumeration typed into text box with LINQ. It's OK with name, but when LINQ reaches values, it throws error: "Conversion from string "Black" to type 'Integer' is not valid". I have read that if I want to obtain a value, then I gotta use conversion function.

Here's code (button's Click event):

Private Sub GetEnums(ByVal sender As Object, ByVal e As RoutedEventArgs)
lstEnums.Items.Clear()
Dim typeName = Type.GetType(txtEnum.Text)
Dim enums = From en In typeName.GetEnumNames

[code].....

.net - Linq-to-Entities: LEFT OUTER JOIN With WHERE Clause And Projection?

Oct 18, 2010

how to translate a simple SQL LEFT OUTER JOIN with a two condition where clause into a working Linq-to-Entities query. There are only two tables. I need values for all rows from Table1, regardless of matches in Table2, but the WHERE clause uses fields from Table2. In SQL, the two parameters would be Table2WhereColumn1 and Table2WhereColumn2, and the query (which works) looks like this:

SELECT t1.Table1Id,
t1.FieldDescription,
t2.FieldValue

[code].....

I've tried using Group Join with DefaultIfEmpty(), as well as an implicit join (without the actual Join keyword), and I only get rows for items that have values in Table2. I'm sure this won't help, but here's an example of the Linq I've been trying that doesn't work:

Public Shared Function GetProfilePreferencesForCedent(ByVal dc As EntityContext, _
ByVal where1 As Int32, _
ByVal where2 As Int32) _

[code].....

Asp.net - LINQ To Entities Does Not Recognize The Method - Simple Delete Statement

Apr 5, 2011

I have a GridView and on a row being deleted I trigger the GridView1_RowDeleting sub, but I receive an error "LINQ to Entities does not recognize the method 'System.Web.UI.WebControls.TableCell get_Item(Int32)' method, and this method cannot be translated into a store expression." Code is:

Private Sub GridView1_RowDeleting(sender As Object, e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles GridView1.RowDeleting
' The deletion of the individual row is automatically handled by the GridView.
Dim dbDelete As New pbu_housingEntities
' Remove individual from the bed.

[code]....

The specific line erroring out is:

remove_bed.First.occupant = ""

LINQ To Entities Does Not Support The Method System.Object CompareObjectEqual?

May 31, 2011

When I execute the code below I receive the error message: LINQ to Entities does not recognize the method 'System.Object CompareObjectEqual(System.Object, System.Object, Boolean)' method, and this method cannot be translated into a store expression.It seems to be occurring on the line For Each row2 in PCstudent.

[Code]...

Linq-to-Entities Aggregate A Column That Is Calculated In An External Function?

Feb 21, 2011

I want to Sum of the calculated column Red which is calculated in the Function IsRed() that return an integer.When I run the query I get the following error: Method 'Int32 IsRed(Int32)' has no supported translation to SQL.How should I rewrite this to get it to work.

[Code]...

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