I'm trying to set a LINQ query as the DataSource of a BindingNavigator control.
In the form's variables I added a data context:
`Private c
tx As New myDataManagerDataContext`
The following code allows me to display and navigate through the results:
Dim clubList = From c In ctx.clubs _
Select c
BindingNavigator1.BindingSource.DataSource = clubList
Each record is displayed nicely so far.
In the Winform, all textboxes are duly binded to the datasource but my problem is:
I added a Save ToolboxButton with: ctx.SubmitChanges()
But it doesn't process any update!
Question: Do I HAVE to write a complete Insert/ Update Linq procedure in the Save button?
Like:
Dim newClub as new DataContext.Club
newClub.Name = NameTextBox.Text
newClub.Address.... Etc.
Try to call EndEdit on binding source just before save operation to happen.
Related
I have a datatable in my dataset that has these fields:
and I have a wpf window that the user inputs data into controls corresponding to these fields. The controls are bound to a datarow as follows:
DataContext = myApp.Tables("VehicleExpenses").NewRow
When I load the form at run time I get this error:
System.InvalidCastException was unhandled by user code
HResult=-2147467262
Message=Conversion from type 'DBNull' to type 'Long' is not valid.
and this is the line that throws the error (this is generated code):
Return CType(Me(Me.tableVehicleExpenses.CategoryIDColumn),Long)
So the error is obvious but I have no idea how to prevent VB from pulling a Null value from the new row. I've tried writing a blocking converter and setting UpdateSourceTrigger = Explicit but neither solves the problem.
--UPDATE 1--
Do not get confused by Dataset and this model. This middle layer is for user interaction and validation purpose. Saving data to db is in 2 stages. You will still need the auto generated properties and methods for CRUD operations.
Imagine this possibility (this is c#)
public class Vehicle
{
public int VehId{get;set;}
public Vehicle(){}
public bool SaveToDb()
{
MyDataSet myDataSet = new MyDataSet();
myDataSet.VehicleExpenses newVehRow = myDataSet.VehicleExpenses.NewVehicleExpensesRow();
newVehRow.VehId = this.VehId;
myDataSet.VehicleExpenses.Rows.Add(newVehRow);
// Save the new row to the database
myDataSet.Update(this.myDataSet.VehicleExpenses);
}
}
Delete the row with that Null value in the table directly (if present).
The DataTable.NewRow creates a new DataRow with column defaults values (since nothing is passed). Not sure why it's not setting default value as 0 for the non-nullable column
Try this option instead of myApp.Tables("VehicleExpenses").NewRow if possible
'declare a VehicleExpenses in the form (you might have to create this class)
Dim blankMo As VehicleExpenses
' in Form_load() set this object with new VehicleExpenses and against Datacontext
blankMo = New VehicleExpenses()
DataContext = blankMo
You will need to add a separate save button and function to commit this model details to the database.
Let us know..
I am using a LINQ-to-Entity Model attached to my database. I can do normal binding using LINQ with no problems, example:
Dim db As New myEntityModel
dim myCustomers As New Customers
myCustomers=db.Customers.ToList
dim myItemSource = From c in myCustomers
Select c
myComboBox.ItemsSource = myItemSource
Easy! But my question is how do I implement INotifyPropertyChanged so that controls that I bind to are automatically updated whenever the data source changes?
Your code doesn't make a whole lot of sense :-)
First:
dim myItemSource = From c in myCustomers
Select c
This is not needed ad all, you can change the last line to this: myComboBox.ItemsSource = myCustomers. No need for myItemSource. This can be further simplified to myComboBox.ItemsSource = db.Customers.ToList. No need for myCustomers either.
Second:
You want your combobox to be updated when the customers change. Then why are you not binding directly to db.Customers but to a static list that will never change? db.Customers.ToList will create a snapshot of the contents of db.Customers. It will not be updated, when db.Customers is updated.
Conclusion:
Your code should look like this:
Dim db As New myEntityModel
myComboBox.ItemsSource = db.Customers
As context, I am new to ADO.NET and have been using 'Programming ADO.NET 2.0' by David Sceppa to help build my knowledge.
I have been trying to understand the Dataset object but think I may have completely misunderstood the point and am looking for guidance.
As an example, I have built a really simple Form with a combobox with an aim of filling the combobox with the names of people in a database ("MyDatabase"). The following code works fine for me:
Private Sub frmEmployee_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim strConn, strSQL As String
strConn = "Data Source=.\SQLExpress;Initial Catalog=MyDatabase;Integrated Security=True;"
strSQL = "SELECT LastName, FirstName FROM EmployeeTable"
Dim da As New SqlDataAdapter(strSQL, strConn)
Dim ds As New DataSet()
da.Fill(ds, "AllEmployeesList")
For i As Integer = 0 To ds.Tables("AllEmployeesList").Rows.Count - 1
Dim row As DataRow = ds.Tables("AllEmployeesList").Rows(i)
cbAllEmployeesList.Items.Add(row("LastName") & ", " & row("FirstName"))
Next
End Sub
Now suppose I have a button on my Form ('GetAge') which is designed to retrieve the age of the employee selected in the combobox from the dataset "AllEmployeesList" and display in a TextBox on the same Form.
The bit I really don't understand is how I can interact with the original dataset that I have created to get the age? It seems to me that the dataset is only in memory during the Load event? If my dataset persists beyond the Load event then where can I find it?
My understanding is that a dataset object is an offline cache of data and has no links to the underlying database.This is useful as it allows you to manipulate the data without keeping a connection open and later on you can submit any changes in the Dataset back to the original database. So once I have built my dataset in the Load event how can I then further interact with it?
I suspect there is a large error in my understanding of what a Dataset object is. Can anybody set me straight?
Thanks to anybody who can help
Alex
A data set can hold multiple data tables, so if you fill that same dataset that already has the "AllEmployeesList" datatable filled, you can fill another datatable with the age under another table name. Picture a dataset as an in-memory database.
You can store the dataset in the datasource of the datagrid view, or make it a form level variable so you can interact with it without casting anytime.
Another part of datasets to be aware of is you can make a design-time dataset so things are more type-safe and explicit.
You seem to have a good grasp on the concept and reason of the DataSet. Your question is really more about managing state than the ins and outs of a DataSet.
You never stated if you are using WebForms, WinForms, or something else. If you're using WinForms, promote the DataSet to be a member variable of the form. It'll stay in memory as long as the form is open.
If you're using WebForms, then this becomes much more complex. This is a good overview to get you started.
Unless your application needs to operate in a disconnected mode, it's not strictly necessary nor always a good idea to cache database data on the client. In this case, you're extracting the age data for all employees without knowing whether you'll ever need it for any of them.
I would just pull the first and last name data (probably using SqlCommand.ExecuteReader) to populate the list box, and then make a separate call to the database to get the age if the user clicks the button. I posted an example of something similar using SqlCommand.ExecuteScalar on your other question.
When a Function or Sub has finished executing, all the variables you declared with the Dim statement will be gone. If you want a variable to exist as long as your form exists then declare a variable outside your Sub/Function:
Public Class frmEmployee
Private dsEmployeeList As DataSet
Private Sub frmEmployee_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
...
dsEmployeeList = New DataSet()
da.Fill(dsEmployeeList, "AllEmployeesList")
...
End Sub
Private Sub GetAge_Click(sender As Object, e As EventArgs) Handles GetAge.Click
Dim iRowIndex As Integer
iRowIndex = cbAllEmployeesList.SelectedIndex 'In this case the rownumber is the same as the index of the selected item in the combobox
'Check to see if an item from the combobox has been selected
If iRowIndex >= 0 Then
txtEmployeeAge.Text = dsEmployeeList.Tables("AllEmployeesList").Rows(iRowIndex).Item("Age").ToString()
End If
End Sub
This code might work but it's not a recommended solution. Like the previous poster said: only get the data you want, when you need it.
You should bind the DataGrid to the DataSet. When reqd you can retrieve the DataSet back from the DataGrid.DataSource and cast it to a DataSet.
Edit: Added sample code
DataSet ds = new DataSet();
// Code to populate DataSet from your DB
...
...
Assign ds to the datasource of data grid
this.dataGridView1.DataSource = ds;
To retrieve the dataset use the code below
DataSet retrievedFromGrid = (DataSet)this.dataGridView1.DataSource;
However, if you need to perform operations on this DataSet a number of times and memory is not an issue, I would suggest you store it in a class variable to avoid the overhead of casting in a DataSet object from the DataGrid again and again.
I have a problem with Linq and ObservableCollections in my WPF application.
Context of the problem:
I've created a very simple SQL database with two tables: User and BankAccounts.
The User Table has an one-to-many relationship with the BankAccounts Table. Next I've created Linq-to-SQL dataclasses, which worked fine ==> the assosiation between the two tables was detected as well.
Next I've created a function to retreive all Users which works fine:
DataClassesDataContext dc = new DataClassesDataContext
var query = from u in dc.Users
select u;
Now suppose I want to add a new BankAccount to each user (not very likely but still).
I could add the following code
for each(User u in query)
{
u.BankAccounts.Add(New BankAccount());
}
The above works all fine. The BankAccounts property is automaticly part of the User class, due to the assosiation in the database and Linq DataClasses.
However, in my application I first add the query results to an ObservableCollection. Hereby I could use all sorts off databinding and changenotification. This is accomplished by the following code;
ObservableCollection<User> oUsers = new ObservableCollection<User>(query);
Problem: Within the ObservableCollection I can't do anyting with the users BankAccounts property because it is now of type EntitySet<>. So I can't do the following statement anymore.
for each(User u in oUsers)
{
u.BankAccounts.Add(New BankAccount());
}
Somehow, when queryresults are added to an observablecollection It is not possible to acces the user.BankAccounts properties anymore. However, it is possible to bind the BankAccounts Property to any control, like a listbox, and it contains the correct data.
Does someone now how I can create an observableCollction (or similar collection) from wich I can access these "assosiated" properties? I'm realy looking forward for to a solution.
Thanks in advance!
Best regards,
Bas Zweeris
E: Bas.Zweeris#Capgemini.com
Keep track of the original query which will implement IQueryable, you can run any further queries you need against that.
The ObservableCollection should just be for WPF to have something to bind to - its very useful if you want to add a new collection item but not have it pushed to the database before the user has had chance to edit it.
eg.
// Create a new blank client type
var ct = new ClientType()
{
IsArchived = false,
Description = "<new client type>",
Code = "CT000",
CanLoginOnline = true
};
// Tell the data source to keep track of this object
db.ClientTypes.InsertOnSubmit(ct);
// Also add the object to the observable collection so that it can immediately be shown in the UI and editted without hitting the db
clienttypes.Add(ct);
I have a grid bound to a BindingSource which is bound to DataContext table, like this:
myBindingSource.DataSource = myDataContext.MyTable;
myGrid.DataSource = myBindingSource;
I couldn't refresh BindingSource after insert. This didn't work:
myDataContext.Refresh(RefreshMode.OverwriteCurrentValues, myBindingSource);
myBindingSource.ResetBinding(false);
Neither this:
myDataContext.Refresh(RefreshMode.OverwriteCurrentValues, myDataContext.MyTable);
myBindingSource.ResetBinding(false);
What should I do?
I have solved the problem but not in a way I wanted.
Turns out that DataContext and Linq To SQL is best for unit-of-work operations. Means you create a DataContext, get your job done, discard it. If you need another operation, create another one.
For this problem only thing I had to do was recreate my DataContext like this.dx = new MyDataContext();. If you don't do this you always get stale/cached data. From what I've read from various blog/forum posts that DataContext is lightweight and doing this A-OK. This was the only way I've found after searching for a day.
And finally one more working solution.
This solution works fine and do not require recreating DataContext.
You need to reset internal Table cache.
for this you need change private property cachedList of Table using reflection.
You can use following utility code:
public static class LinqDataTableExtension
{
public static void ResetTableCache(this ITable table)
{
table.InternalSetNonPublicFieldValue("cachedList", null);
}
public static void ResetTableCache(this IListSource source)
{
source.InternalSetNonPublicFieldValue("cachedList", null);
}
public static void InternalSetNonPublicFieldValue(this object entity, string propertyName, object value)
{
if (entity == null)
throw new ArgumentNullException("entity");
if(string.IsNullOrEmpty(propertyName))
throw new ArgumentNullException("propertyName");
var type = entity.GetType();
var prop = type.GetField(propertyName, BindingFlags.NonPublic | BindingFlags.Instance);
if (prop != null)
prop.SetValue(entity, value);
// add any exception code here if property was not found :)
}
}
using something like:
var dSource = Db.GetTable(...)
dSource.ResetTableCache();
You need to reset your BindingSource using something like:
_BindingSource.DataSource = new List();
_BindingSource.DataSource = dSource;
// hack - refresh binding list
Enjoy :)
Grid Data Source Referesh by new query instead just Contest.Table.
Simple Solution < But Working.
Whre is eg.
!!!!! Thanks - Problem Solved after no of days !!! but with so simple way ..
CrmDemoContext.CrmDemoDataContext Context = new CrmDemoContext.CrmDemoDataContext();
var query = from it in Context.Companies select it;
// initial connection
dataGridView1.DataSource = query;
after changes or add in data
Context.SubmitChanges();
//call here again
dataGridView1.DataSource = query;
I have the same problem. I was using a form to create rows in my table without saving the context each time. Luckily I had multiple forms doing this and one updated the grid properly and one didn't.
The only difference?
I bound one to the entity similarly (not using the bindingSource) to what you did:
myGrid.DataSource = myDataContext.MyTable;
The second I bound:
myGrid.DataSource = myDataContext.MyTable.ToList();
The second way worked.
I think you should also refresh/update datagrid. You need to force redraw of grid.
Not sure how you insert rows. I had same problem when used DataContext.InsertOnSubmit(row), but when I just inserted rows into BindingSource instead BindingSource.Insert(Bindingsource.Count, row)
and used DataContext only to DataContext.SubmitChanges() and DataContext.GetChangeSet(). BindingSource inserts rows into both grid and context.
the answer from Atomosk helped me to solve a similar problem -
thanks a lot Atomosk!
I updated my database by the following two lines of code, but the DataGridView did not show the changes (it did not add a new row):
this.dataContext.MyTable.InsertOnSubmit(newDataset);
this.dataContext.SubmitChanges();
Where this.dataContext.MyTable was set to the DataSource property of a BindingSource object, which was set to the DataSource property of a DataGridView object.
In code it does looks like this:
DataGridView dgv = new DataGridView();
BindingSource bs = new BindingSource();
bs.DataSource = this.dataContext.MyTable; // Table<T> object type
dgv.DataSource = bs;
Setting bs.DataSource equals null and after that back to this.dataContext.MyTable did not help to update the DataGridView either.
The only way to update the DataGridView with the new entry was a complete different approach by adding it to the BindingSource instead of the corresponding table of the DataContext, as Atomosk mentioned.
this.bs.Add(newDataset);
this.dataContext.SubmitChanges();
Without doing so bs.Count; returned a smaller number as this.dataContext.MyTable.Count();
This does not make sense and seems to be a bug in the binding model in my opinion.