When I try to query an entity that has a varbinary field in it I am getting error:"The LINQ expression node type 'ArrayIndex' is not supported in LINQ to Entities."
Here is my query:
Dim query = From entity In db.Entity
Where entity.Id= Id
Select entity.VarBinaryField
[code]....
The error gets generated when I check that the query isNot nothing.
A partner of ours is making a call to a web service that includes a parameter called token. Token is the result of an MD5 hash of two numbers, and helps us authenticate that the user using our partners system. Our partner asks the user for two strings, concatenates them, runs them through MD5, and then calls our web service. The result of the MD5 is the token, and it is submitted to us as a string.
We store valid tokens in a DB - since we use the SQL Server to compute the tokens on our end, SQL seemed to be happiest storing the tokens as a varbinary, which is its native result for an MD5 computation.
We have two pieces of code that attempt to do the same thing - run a select query that pulls out a value based on the token submitted. One uses a dynamic query (which is a problem), but it works. The other one attempts to do the same thing in a parameterized (safer) fashion, it does not work - it is unable to locate the token.
Here's the two competing attempts. First, the parameterized version which fails:
byteArrayToken = System.Text.UnicodeEncoding.Unicode.GetBytes(stringToken)
scSelectThing.CommandText = "select thing from tokenstable where token=@token"
Dim param As SqlParameter = scSelectThing.Parameters.Add("@token",
[Code].....
I'm trying to test a varbinary(max) field to see if it's null. I'm trying to figure out if it's a null or not in the select statement, hoping to avoid having to do this locally for every row of the returned dataset. This is the SQL I'm using,
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I use a VARBINARY(MAX) column, because I have no idea what is going to be put into it. All I know is that as of this point in time, the data will be one of many traditional data types(Integer, String, DateTime, etc.)I also have another column that is meant to indicate the DataType so the .NET application can handle the data and validate input accordingly.Right now, for testing, I have a DataType table in my database that stores the "supported" datatypes for the VARBINARY column, and a foreign key linking to the column meant to indicate the DataType. This works perfectly, but it feels akward.
View 2 RepliesI am trying to build a survey engine from an existing database design which is like this.
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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
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Given the following XML file:
<users>
<user name="admin" password="foobar" roles="Admin,Guest" />
<user name="guest" password="foobar" roles="Guest" />
</users>
How do I find a specific node? In this case I want to find the node that has its name attribute to be "admin"
Dim authGroup As XElement = XElement.Parse(myXMLDoc.OuterXml)
Dim foundUser As IEnumerable(Of XElement) = From i In authGroup.Elements Where i.Attributes("name") = "admin" Select i
[Code].....
I have been looking into dynamic querying of datasets and the use of copytodatatable() for a project. I have seen in alot of forums that the copytodatatable functionality is unusable as it was removed. have an example of a dynamic Linq query being loaded into a datatable.
View 1 RepliesHow do I return a top 5 with rank number using linq?
Dim Top5 = From A In DAO.Cache.Select(Of VO.Empresa).Take(5) Select A.Nome
I would like this result:
Rank Name
1 "Example Name"
2 "Example Name"
3 "Example Name"
4 "Example Name"
5 "Example Name"
I am trying to query from search box using list of data and the linq I used is:data = (From k As BSPLib.ContactLib.Contact In data_org.Values Where k.stringdata Like "%" & Searchtxtbox.Text & "%" Select k.prime).ToListBut this is not working, I am getting no data at all. Data_org is a dictionary so I used the values; k.stringdata contains all the data that need to be searched. Searchtxtbox.text contains the user defined search item.I Tried with sqlmethods through linq, but sqlmethods does not exist for me, I tried with with Imported namespace yet the code is not showing sql methods, could you please provide a workable query or just tell me where I have gone wron
View 2 RepliesI am having a little problem with some homework. Here is the problem:Use the Invoice Class provided to create an array of Invoice Objects. Class Invoice includes four properties- a PartNumber (type integer), a PartDescription (type String), a Quantity of the item being purchased (type Integer), and a Price (type Decimal). Write a Console Application that performs the following queries on the array of Invoice objects and displays the results:
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Use the Invoice Class provided to create an array of Invoice Objects. Class Invoice includes four properties- a PartNumber (type integer), a PartDescription (type String), a Quantity of the item being purchased (type Integer), and a Price (type Decimal). Write a Console Application that performs the following queries on the array of Invoice objects and displays the results:
a. Use LINQ to sort the Invoice Objects by PartNumber
b. Use LINQ to sort the Invoice objects by Price
c. Use LINQ to select the PartDescription and Quantity and sort the results by Quantity
d. Use LINQ to select from each Invoice the PartDescrition and the value of the Invoice (i.e. Quantity * Price). Name the calculated column InvoiceTotal. Order the results by InvoiceTotal.
e. Using the results of the LINQ query in Pard d, select the InvoiceTotals in the range of $200 to $500
I am pretty sure I have parts a, b, & c completed correctly. Or at least the provide the desired results. Part d I figured out how to multiply the 2 fields but can't create a new column for the result or figure out how to show the PartDescription with the multiplied result. Part c I think I can figure out when I get part d. I already coded what I think will work for part c.
Below are the 2 Objects the Invoice was given and not to be changed & the LINQ is the one I have been working on.
Module LINQ
Sub Main()
' array of invoices
Dim invoices As Invoice() = { _
New Invoice("83", "Electric Sander", "7", 59.98), _
[Code] .....
I have some basic expirience in Visual Basic and programming Windows Forms programs. I know now that forms programs are no longer updated by Microsoft and that WPF is the way to go. No to mention the slicker interface you can create. I've also noticed that passing SQL strings to a database is no longer the standard either. It's either Entity Framwork or Linq.
So I am going for a fresh approach. I need to develop a program that will access a sql database and be accessed by about 10 concurrent users within the office. What's the best approach in general? Linq or Entity Framework? Also, could you recommend a book or two for someone who is new to WPF and Entity Framework? I do have some programming expirience, just none with WPF or the new ways of ADO.net 4.
I can't figure out that linq to entity query syntax. My problem is that if the value of the Calls table is null then noting comes up, I want to make something like a left join to get 'all' rows from the Calls table.I tried to group it but I can't figure out the correct way to write it.
Dim TicketQuery As ObjectQuery = From c In EnData.Customer _
Join t In EnData.Calls On t.CustomerID Equals c.CustomerID _
Join Status In EnData.Lists On t.Status Equals Status.ListValue _
[code].....
I'm using Entity Framework in Visual Studio 2010 Beta 2 (.NET framework 4.0 Beta 2). I have created an entity framework .edmx model from my database and I have a handful of many-to-many relationships.
A trivial example of my database schema is
Roles (ID, Name, Active)
Members (ID, DateOfBirth, DateCreated)
RoleMembership(RoleID, MemberID)
[Code]....
For brevity I turned the list of all the columns from the Members table into *
As you can see it's just ignoring the "Role" query.
I am using LINQ to SQL queries to return data in my application. However I find it is now needful for me to return the column Names. Try as I might I have been completely unable to find out how to do this on the internet.
So if my LINQ entity table has the properties (Last_Name, First_name, Middle_Name) I need to return[code]...
I am wanting to create a Where statement within my Linq statement, but have hit a bit of a stumbling block.I would like to split a string value, and then search using each array item in the Where clause.In my normal Sql statement I would simply loop through the string array, and build up there Where clause then either pass this to a stored procedure, or just execute the sql string. But am not sure how to do this with Linq to Entity? ( From o In db.TableName Where o.Field LIKE Stringvalue Select o ).ToList()
View 5 RepliesThis is my function:
Public Function GetAllEmployee() As List(Of Employees)
Return DB.Employees.Select(Function(q) New With {q.EmployeeID, q.LastName,q.FirstName}).ToList()
End Function
I'm getting an error:
Value of type System.Collections.Generic.List(Of <anonymous type>) cannot be converted to System.Collections.Generic.List(Of NorthwindModel.Employees).
I have the following code, that in my head should create a new row in a table:
Dim fin As Boolean
Dim db2 As New ChecklistModeldbmlDataContext
For Each a In bServers
If collection("fin" & a.ServerName) = "true, false" Or collection("fin" & a.ServerName) = "true,false" Then
[Code]...
It only ever adds one record in to the table and then errors with Cannot add an entity that already exists.
Now it should enter 4 rows into the table, but I can't work out why the above gives me that error.
I've also tried having the db2.SubmitChanges() outside of the for each and it just inserts the last row.
I'm taking a peek at both the Entity Framework and LINQ to SQL, and while I like the systems (and of course the LINQ integration) I'm a little skeptical on the data-binding aspect. I've taken query results and inspected them, and they don't appear to implement the standard .NET list-binding interfaces (IBindingList, and more importantly ITypedList), leading me to believe that binding them to a grid (or anything else) is going to use reflection to get/set my entity properties. This seems like a comparatively expensive operation, especially when all of the code is generated anyway and could implement the interfaces. Is reflection used to get/set the value of the properties?
Edit: I'm actually concentrating on whether or not ITypedList is implemented somewhere along the way, as that's what has the capability to provide an explicit mechanism for defining and interacting with properties without resorting to reflection. While I didn't have a LINQ to SQL project up,I did inspect a simple Entity Framework entity query result, and it did not appear to implement ITypedList.
Edit 2: After accepting Marc's answer, I thought it might be helpful for others if I posted some simple code I used to seamlessly implement his solution. I put the following in the static constructor for my class:
public static ContextName()
{
foreach(Type type in System.Reflection.Assembly.GetExecutingAssembly()[code]....
While this is for LINQ to SQL, I'm sure an equivalent version could be written for the Entity Framework. This will scan the assembly for any types with the Table attribute and add a custom provider for each of them.
I have a simple If..Then like so:
If rhcexists.First.SignatureDate > Date.Today.AddMonths(-6) Then
End If
rhcexists is a simple query to the Entity Model:
[code].....
I've seen many examples in LINQ but i'm not able to reproduce the same result in vb.net.
I have following code: Dim context As New MyModel.Entities()
Dim rnd As New System.Random()Dim gardens As List(Of Tuin) = (From t In context.Gardens Where _
t.Approved = True And _
Not t.Famous = True _
Order By rnd.Next() _
Select t).ToList()
[Code]...
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?
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]
View 1 RepliesI 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].....
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.
I'm trying to check if a LINQ Entity exists in its table, but at design time I dont know what type that entity is. So I figure I'll just get the table, and try the Contains method on it. But I cant get the table in such a way that I can query it at design time.I've tried the GetTable method on the datacontext, but I dont know how to cast it to the appropriate type when using GetTable(Of). GetTable(Type) works, I just use Entity.GetType(), but then I don't know how to query the ITable thats returned.To try and cast the ITable to something useable, I created an interface(IWhatever) that could implement properties that are native to all of my entities I would encounter. [code]
View 2 RepliesI just read this article about the Entity Framework 4 (actually version 2).Entity Framework seems to offer a huge improvement over its first release. Thus, I have never ever used EF in any project, since I think EF is not mature enough in comparison to NHibernate.NHibernate and its current contributions of FluentNHibernate and Linq for NHibernate by Ayende RahienMy feeling is that Microsoft is solely trying to gain terrain it has lost in favor of NHibernate when the 2nd version of NHibernate came out.Nevertheless, my concerns are the followings (not in particular order):Will EF4 tend to be less XML-verbose?Will EF4 be compatible with other underlying datastore than just SQL Server?What are the greatest benefits of going with EF4 instead of FluentNHibernate or NHibernate itself.
NHibernate is a great tool, I guess everyone agrees. Due to its predecessor Hibernate, we may easily find documentions and tutorials and sample applications to get acquainted with it. This is not the case for FluentNHibernate. Particularly as per the project I'm working on right now which demands that I investigate further about NHibernate and its options (FluentNHibernate for instance) in order to document the rules of usage and the best practices of NHibernat and FluentNHibernate technology. Thus, being handcuffed with VB.NET, being a C-Style developer, I can't find some syntax equivalencies in VB.NET for the examples provided, though I made I way so far
I am using database compact and i loaded it on my form and i want to update a single field but I cannot, why:
what am doing is:
dim newrec as datatable=(studentdataset."TableName")
dim querie= from det in newrec.asnumerable() _
[code].....
I wanted code to convert the varbinry to pdf and save it on Clients machine.
View 4 RepliesI want to update an entity without loading the entity from the database first. I've accomplished this but only by knowing all of the entities properties and then using the "attachto" method. My issues is i don't want my app to need to remember all of the properties. Example:
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