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 have a Microsoft Access database that I connect to with the Jet Database Engine, using VB.NET. I want to programmatically get all of the column names for a particular table [code]...
Is this possible in Access? If not, what are my options for getting the column names?
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]...
In LINQ, I'd like to project different names than those from the database tables. "Friendly names" that I can use for column headers. Names that have "%" or possibly a " " (space). The query below won't compile.
Is something like that possible or am I stuck using the dreaded _ underscore for everything?
CODE:
I have a DataGridView which populates from an SQL query just fine in default mode
using these table names
[firstName] [varchar](20) NOT NULL,
[lastName] [varchar](20) NOT NULL,
[code]....
I have edited the column headers and set the column names to the same values as my table names yet the data is not showing in form load I have set datagridview.AutoGenerateColumns = False I know the data is there if I delete datagridview.AutoGenerateColumns = False then the data is shown with the default headings?
I'm writing a solution where the data entities are passed to clients using datasets through a WCF service, with nHibernate as ORM. My predecessor has written some translator classes, converting datasets to entities and vice versa. In most cases he's declared the return object as a parameter for the object.
For example:
Public Shared Function CreateEntity(ByVal ds As DataSetObject, ByVal entity As EntityObject) As EntityObject
Dim row As ds.EntityObjectRow = ds.EntityObject(0)
entity.Id = row.Id
[code]....
He's not with the company anymore, so I can't ask him why he's done it this way. Hence my question here. Is there some performance gain, or traceablity thing with nHibernate by using the first implementation rather than the latter?
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.
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.
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].....
So, when you bind a collection of Entity objects to a grid component, the grid displays those fields in the sequential order they are found in the SQL Table they came from. This shows that the ordinal position of the fields are associated with their corresponding entity properties... somehow or other.
So here is the question: How can I obtain the table field ordinal position by reflecting over an Entity Framework Entity's properties? Let me tell you what I know and what I have tried. Apparently, each data field property in an EF Entity is decorated with a System.Runtime.Serialization.DataMemberAttribute. This attribute appears to have an Order property. However, I have discovered that this property does not contain what I am looking for. The value for all Data Properties in an Entity seems to be -1. What ever order is, it isn't ordinal position.
I'm brand new to the Entity Framework and trying to learn all it can offer. I'm currently working my way through the MVC Music Store tutorial which includes the following code:
public ActionResult Browse(string genre) {
// Retrieve Genre and its Associated Albums from database
var genreModel = storeDB.Genres.Include("Albums")
.Single(g => g.Name == genre);
return View(genreModel);
[Code] .....
The problem is I'm getting the following exception:
Invalid column name 'GenreGenreId'.
Which I know is true, but I can't for the life of my work out where it's getting 'GenreGenreId' from.
Here is the source for my classes:
Album.vb
Public Class Album
Private _title As String
Private _genre As Genre
Private _AlbumId As Int32
[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'm developing a user control that exports a grid view to many file formats, this control takes the gridview as a property, I need a code that returns the gridviews in the form if so that in design time user can choose one to export
View 3 Repliesi'm trying to get my program to look up a string and find a match in an access database in column "PhoneNumber" and return the value from column "FullName" on the same row to a different string
so it would go like this: (i really don't know much about accessing databases)
Dim PhoneNumber As String
Dim FullName As String
PhoneNumber = TextBox1.Text
FullName =
im pretty much a beginner to using ASP.net and linq to sql but what im trying to do is update a column of a table based on a variable. at the momment i have
Dim db As New sqldcDataContext Dim update As tableName = (From i in db.tableNames _ Select i)
i think this selects everything, how could i have two variables, one to store what table to update and the other what column. is this possible?edit: sorry for being unclear im trying to make this as dynamic as possible so i dont have to type in the exact table/col names. something like this but in the linq to sql syntax.
mysql_query("SELECT * FROM ". $table ." WHERE `" . $column . "` = "" . $data ."");
I would like the following function to return Nothing if the element with the specified key is not in the collection. Instead, it returns an error - something to the effect of "no element found"
Public Class MyCollection
Inherits System.Collections.ObjectModel.Collection(Of MyType)
Public Function FindByActivityKey(ByVal searchValue As Integer) As MyType
[code]....
I'm quite new to Visual Basic - using Visual Studio 2008 and can't seem to find a way to do the following:
I have a few tables in a SQL Server database and have used LINQ to SQL to create classes of those tables.
Here's a cut down example of what I'd like:listbox1 filled with table names - APS, SMPS, WCPC, CFLAPS
Then from the SelectedIndexChanged event, listbox2 should populate column headers of the selected table.
I have no issues getting data from the database, and can access all of these headers through the anonymous type objects created from a LINQ query (eg APS.ID, APS.count etc), but populating a listbox with these variable names rather than the data inside them seems rather elusive.
This is probably a cross platform coding question rather than VB specific, so if you have a solution in C# or whatever I'd be happy if you could let me know.
i recently posted a code that i had that i needed assistance for and it was solved it was for displaying all tables in a database.but now i have this code for showing all column names in a table i was in the process of turning it from oledb to sqlclient. GetOLedbSchema can be turned to getschema but when it comes to OleDbSchemaGuid
Public Shared Function getAllColumnNames(ByVal tblname As String) As String()
Dim com As New SqlCommand
Dim con As SqlConnection
[Code].....
i have this code for showing all column names in a table i was in the process of turning it from oledb to sqlclient. GetOLedbSchema can be turned to getschema but when it comes to OleDbSchemaGuid
Public Shared Function getAllColumnNames(ByVal tblname As String) As String()
Dim com As New SqlCommand
Dim con As SqlConnection
[Code]......