.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]....

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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]

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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].....

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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!

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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]....

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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.

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.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.

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Put Two Linq Query Results Together?

Sep 11, 2009

I have used linq quite abit but was just wondering how to append the results of two IEnumerable(of X) together into one IEnumerable(of X)

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Asp.net - LINQ-to-SQL Query Returning No Results?

Mar 5, 2011

I have a query using LINQ-to-SQL. It queries an underlying database table Rooms. It uses Where conditions to narrow down the results, namely:

Gender.Current Occupancy < Max Occupancy Available Flag is Checked I know this should return results but it keeps returning an empty set.Code is below

[code]...

UPDATE: I've verified that the issue is with the statement where sh.is_available = 1, which doesn't make sense since this is a bit field.

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LINQ To XML Query Returning No Results?

Jul 20, 2011

I'm doing some XLINQ in VB for work. I basically need to pull some values from a small chunk of XML as listed here:

<?xml version="1.0" encoding="utf-8"?>
<Fields>
<typeQtyRadioButtonList>1</typeQtyRadioButtonList>
<cmbQtyCheck>Reject</cmbQtyCheck>

[code]....

... Leaving out the implementation of the For Each loop....So I have stuck a break point on the for each and the collection has no elements in it.

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Possible To Change &amp; To & In The Results From A LINQ Query?

Mar 3, 2009

I have the following code:

Dim db As New linqclassesDataContext
Dim categories = (From c In db.faq_cats)
NewFaqDropDownCategory.DataSource = categories

[code]....

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.net - Linq Query Ignore Empty Parameters?

Apr 20, 2010

How do I get Linq to ignore any parameters that are empty? So Lastname, Firstname, etc? If I have data in all parameters it works fine...

refinedresult = From x In theresult _
Where x.<thelastname>.Value.TestPhoneElement(LastName) And _
x.<thefirstname>.Value.TestPhoneElement(FirstName) And _
x.<id>.Value.TestPhoneElement(Id) And _

[code]....

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C# - Linq To XML Query Creating Empty Items From XML

Feb 15, 2010

why is this xml

<?xml version="1.0" encoding="utf-8"?>
<items>
<item id="77" cityID="EE12345" cityDatum="15.2.2010. 11:28:35" />
</items>

[Code]....

If you, as some can't replicate these results, here's a screenshot:

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Joining LINQ Query Results For Each Item Together?

Feb 3, 2011

In my application, I have a search query textbox (txtSearch) that works well with one-word queries with the following LINQ:[code]So how would I make the above query more generic (ie: able to handle any number of words in a query)?I should note that the object being queried is a List of strings pulled from an Access database. As it stands, this application only queries the database once and I'd like to keep it that way if possible.

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.net - LINQ Query Returns List Of Empty Objects?

May 3, 2012

I have a query that 'selects' object of a type:

Dim l as IList(Of Foo) = (From dataRow As DataRow In table.Select()
Where CStr(dataRow("Column1")) = "A"
Select New Foo(CStr(dataRow("Column1")), _
CStr(dataRow("Column2")))).ToList()

What's happening is that if i set a break-point to the constructor of Foo and step, the constructor is hit and the parameters are loaded with the arguments. However, l has empty Foo objects (the members in every object are Nothing). What could be happening here?

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Iterate Through LINQ Query - Results From Multiple Tables

Dec 7, 2010

I have a VB .Net linq query that I want to return values from two tables. I currently have this:
Dim query = (From c In db.Client _
Join u In db.Users _
On u.UserID Equals c.UserID _
Where (c.ClientID = 1)
Select c, u).ToList
query (System.Collections.Generic.List(Of )) returns several rows as expected each item containing a c and a u.
How do I iterate through the queries collection?

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Using LINQ To Query XML And Return Empty String If No Data Is Present?

Mar 8, 2011

What I'm trying to do is to write a generic rss reader that I plug in any URL into without worry if the feed has all the common properties. For instance in my example below I'm looking for pubDate, however if no pubDate exists in the xml I'd like to return the current Date. I cannot seem to get the syntax right though.

Dim xmldoc As New XDocument
xmldoc = XDocument.Load(url)
Dim feeds = From feed In xmldoc.Descendants("item") Select New With { _

[code].....

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Filter Parent / Child Table In Linq Query Based On Entities In Child Table?

Jul 9, 2010

I have a table (Projects) which is linked to projectVersions on projectID..projectVersions contains several columns on which I'd like to filter a returned project (and associated projectVersions) list. For example there is a "capacity" column and a "country" column. I am doing a filtered list of projects on one page and I'd like to include all projects where any one of the associated projectVersions has a capacity of 750ml and a country of "France" for example.It may be that a particular parameter is not set and so I pass a zero to indicate not to filter on that.I guess this needs some kind of subquery as when I try and do something like this: [code] it doesn't work as the "xxx" bit, being one-to-many, expects me to specify an item to get at the entities within and yet I want to query where ANY of the associated versions match one of the criteria.

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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].....

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.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.

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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?

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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]....

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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

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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?

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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.

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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]...

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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?

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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]...

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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?

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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]...

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