I store encrypted email addresses in my Database and use the DoDecrypt Function of mine, to display the unencrypted email addresses in a AspGrid
So my LINQ query is something like
Dim Query = From c In DB.Something Select New With {.Email = DoDecrypt(c.Email)}
Which returns a set of the emails in debug mode...
After using a Linq to datatable function the results returned are the ones found in the Database, which are the encrypted ones.
What is going wrong here?
How should i modify my Linq query?
And here is the Linq to datatable function
Public Shared Function ToDataTable(DB As System.Data.Linq.DataContext, query As Object) As DataTable
If query Is Nothing Then
Throw New ArgumentNullException("query")
End If
Dim cmd As IDbCommand = DB.GetCommand(TryCast(query, IQueryable))
Dim adapter As New SqlDataAdapter()
adapter.SelectCommand = DirectCast(cmd, SqlCommand)
Dim dt As New DataTable("sd")
Try
cmd.Connection.Open()
adapter.FillSchema(dt, SchemaType.Source)
adapter.Fill(dt)
Finally
cmd.Connection.Close()
End Try
Return dt
End Function
You need to actually resolve the query, it is late bound by default, but if you're actually wanting to resolve the query, you need to just call .ToList(). I've just wrapped your query in brackets below and called .ToList() at the end. Not sure if this is the exact VB syntax (going from C# knowledge here), but the principal is still the same.
Dim Query = (From c In DB.Something Select New With {.Email = DoDecrypt(c.Email)})
.ToList()
Related
Private Sub ButtonSubmitID_Click(sender As Object, e As EventArgs) Handles ButtonSubmitID.Click
Dim comm As New SqlCommand
Dim conn As New SqlConnection
conn.ConnectionString = "Data Source = localhost\SQLEXPRESS; Initial Catalog = test2Forms; Integrated Security = SSPI;"
comm.Connection = conn
Dim ID = TextBoxID.Text
comm.Parameters.AddWithValue("#ID", ID)
Dim adapter As SqlDataAdapter = New SqlDataAdapter(comm.CommandText, comm.Connection)
comm.CommandText = "SELECT * FROM withActivityLog3 WHERE ID = #ID"
Dim records As DataSet = New DataSet
adapter.Fill(records)
DataGridView2.DataSource = records
End Sub
CommandText property has not been initialized is the error I am receiving. I am able to pull all the data from the database into the GridView on the Form Load but when I try to narrow it down to one ID using a WHERE clause on the button trigger, it comes up with the above error. I've used the debugger to trace through one step at a time and the command and connection strings look correct. I've also successfully duplicated the query on my database using the SQL Server command line. I'm searching on a primary key (ID) so the expected results would be one uniquely identified row from the database.
As for the problem you know you have:
' initialize DataAdapter with (EMPTY) commandtext
Dim adapter As SqlDataAdapter = New SqlDataAdapter(comm.CommandText, comm.Connection)
' initialize Command Text
comm.CommandText = "SELECT * FROM withActivityLog3 WHERE ID = #ID"
When you pass the CommandText to the DataAdapter, it is empty because you havent set it yet which results in the error.
There is a fair amount of inefficiency in your code though. Rewritten:
' form level conn string
Private TheConnString As String = "Data Source = localhost\..."
Private Sub ButtonSubmitID_Click(sender ...
Dim dt As New DataTable
Using dbcon As New MySqlConnection(TheConnString)
Using cmd As New MySqlCommand("select * from Sample where Id = #id", dbcon)
cmd.Parameters.Add("#id", MySqlDbType.Int32).Value = Convert.ToInt32(TextBox2.Text)
dbcon.Open()
dt.Load(cmd.ExecuteReader)
dgvA.DataSource = dt
End Using
End Using
End Sub
Note: this uses MySQL but the concepts are the same for Sqlite, Access, SQL Server etc
There is no need to type or paste the connection string and over everywhere it is used. One form level variable will allow DRY (Dont Repeat Yourself) code.
Anything which implements the Dispose() method should be disposed of. That includes nearly all the DB Provider objects. The Using statement allows you to declare and initialize an object and at the End Using it is disposed of. Failing to Dispose of things can cause leaks and even run out of connections or resources to create things like DB Command objects.
There is no need to create a local DbDataAdapter. These are very powerful and useful critters meant to do much more than fill a DataTable. If that is all you are doing, you can use ExecuteReader method on the DbCommand object.
Nor do you need a local DataSet. Contrary to the name, these do not hold data, but DataTables. Since there is only one and it is local (goes out of scope when the method ends), you dont need a DataSet to store it.
The Add method should be used rather than AddWithValue. The code above specifies the datatype for the parameter so there is no guesswork required of the compiler. Of course with that comes the need to convert the text to a number...
...Since this is user input, you should not trust the user, so Integer.Tryparse would be more appropriate: I like pie will not convert to an integer. Data Validation is something you should do before you commence the DB ops.
Dim ID = TextBoxID.Text as used is pointless code. You do not need to move the textbox text into a new variable in order to use it. However, ID might be used to store the integer value
Okay, I'm creating an application which requires the user to input there Gamer-Tag during the registration process. Only 'Members' of a group may have access to the program and so I need the application to refuse anyone who's Gamer-Tag is not in the SQL Server database.
I adapted a function I created to log-in with your details and changed it to check if the Gamer-Tag is on the database, but I'm receiving a strange error:
The column 'Gamer_Tag' is not a Member of 'Members_Details' Table.
Please note, that's an error and not what I am wanting it to do. It's saying the column 'Gamer_Tag' isn't in the table, but I know it is! I've checked spelling and spacing and everything's as it should be, so I'm assuming it's something wrong with the code.
The (relevant) register button code:
(Note, RegUserName.Text is the textbox that contains the users Gamer-Tag.
Dim dbManager As New DatabaseManager()
If dbManager.CheckGamerTagisMember(RegUserName.Text) Then
MsgBox("Gamer-Tag Not A Member.")
My.Settings.RegisterCount = 1
My.Settings.Save()
RegisterBTN.Enabled = True
MsgBox("Registration Failed.")
GoTo Ender
Else
MsgBox("Gamer-Tag is A Member.")
GoTo Ender
End If
And the function this is calling:
Public Function CheckGamerTagisMember(ByVal gamertag As String) As Boolean
Connection = New SqlConnection("Data Source =" & My.Settings.ServerIP & ";Initial Catalog=Members_Details;Integrated Security=False;User=" & My.Settings.UserName & ";Password=********;")
Connection.Open()
Dim gamertagDatSet As New DataSet()
usersDataAdapter.FillSchema(gamertagDatSet, SchemaType.Source, "Members_Details")
usersDataAdapter.Fill(gamertagDatSet, "Members_Details")
Dim table As DataTable = gamertagDatSet.Tables("Members_Details")
For i As Integer = 0 To table.Rows.Count - 1
Dim currentUsergt As String = table.Rows(i)("Gamer_Tag").ToString.Trim()
If (currentUsergt = gamertag) Then
gamertagDatSet.Dispose()
Connection.Close()
Return True
End If
Next
gamertagDatSet.Dispose()
Connection.Close()
Return False
End Function
And to prove the column is in the table, here's the table's columns;
I'm new to structuring my code into classes, so I could be 'passing' things around wrongly.
Any help would be much appreciated!
I haven't a clue what the issue is with your code (there's probably something else going on which is not evident in your question).
But I will say that the approach you are taking will not scale well. With each registration, you are downloading the entire table to the program and then scanning through the rows, one by one, looking for an ID.
It would be much easier to write a simple stored procedure to do this for you. You would also get the advantage of using indexes. For example:
CREATE PROCEDURE spGetMembers_ID
#Gamer_Tag varchar(255)
AS
SET NOCOUNT ON;
SELECT Members_ID
FROM Members_Details
WHERE Gamer_Tag = #Gamer_Tag
GO
You can call this stored proc this way:
Dim getMembers_IDCommand As New SqlCommand("TestProcedure", Connection)
getMembers_IDCommand.CommandType = CommandType.StoredProcedure
Dim gamerTagParam As SqlParameter = getMembers_IDCommand.Parameters.Add("#Gamer_Tag", SqlDbType.VarChar, 255)
gamerTagParam.Value = gamertag
SqlDataReader result = getMembers_IDCommand.ExecuteReader();
Dim exists As Boolean = myReader.Read()
result.Close()
Return exists
There, of course, many ways to execute a stored procedure and get the results. Several are documented here. But the point is that a stored procedure is faster, more scalable and generally faster.
I was wondering what is the most basic way to avoid the following.
con.ConnectionString = connection_String
con.Open()
cmd.Connection = con
'database interaction here
cmd.Close()
I keep making those lines all over in my project, but I figure there has to be a better way to save on typing this over and over. It makes the code look even more sloppy than it already is!
Ended up with this, works well for me. Thanks for the help :)
Public Sub connectionState()
If con.State = 0 Then
con.ConnectionString = connection_String
con.Open()
cmd.Connection = con
Else
con.Close()
End If
End Sub
This is where a lot of programmers are tempted to create a "database layer" with a variations on method signatures that look like this:
Public DataSet ExecuteSQL(ByVal sql As String) As DataSet
That allows you to isolate all that boilerplate connection code in one place. An sql command string goes in, and data comes out. Easy.
Don't do it!
This is headed in the right direction, but has one very big flaw: it forces you to use string manipulation to substitute parameter values into your sql queries. That leads to horrible sql injection security vulnerabilities.
Instead, make sure you include some mechanism in your methods to prompt for the sql parameters separately. This usually comes in the form of an additional argument to the function, and could be as simple as an array of KeyValuePairs. If you're comfortable with lambdas, my preferred pattern looks like this:
Public Iterator Function GetData(Of T)(ByVal sql As String, ByVal addParameters As Action(Of SqlParameterCollection), ByVal translate As Func(Of IDatarecord, T)) As IEnumerable(Of T)
Using cn As New SqlConnection("connection string"), _
cmd As New SqlCommand(sql, cn)
addParameters(cmd.Parameters)
cn.Open()
Using rdr As SqlDataReader = cmd.ExecuteReader()
While rdr.Read()
Yield(translate(rdr))
End While
End Using
End Using
End Function
To call that function, you would do something like this:
Dim bigCustomers = GetData("SELECT * FROM Customers WHERE SalesTotal > #MinSalesTotal", _
Sub(p) p.Add("#MinSalesTotal", SqlDbType.Decimal, 1000000), _
MyCustomerClass.FromIDataRecord)
You can try creating a class ( a singleton class ), and write the database connection syntax code and exceptions in that class, then call one object to the main class to create the database connection, that's the best way in performance and keep writing the same code on and on...
You can use just using block, using execute dispose on non managed object in the end of treatment.
Link : http://msdn.microsoft.com/en-us/library/htd05whh(v=vs.80).aspx
I would like to fill a datatable with results from a SQL select statment but using a transaction. The reason that I am using a transaction is because I have a list of names (as a datatable), and I want to iterate through the list of names and select the database rows where the name = the name on the list. There are 500,000 names in the database and I only want to retreive the relevant rows. I have the code for the procedure as I think it should look like (untested) BUT I dont know HOW to place the data into a datatable .... so Im missing something where I declare the datatable and the 'fill' of that table , could someone help with this ? Or suggest how else I can get the information out of the batabase without looking up each name individually.
Using connection As New SQLite.SQLiteConnection(R2WconectionString)
connection.Open()
Dim sqliteTran As SQLite.SQLiteTransaction = connection.BeginTransaction()
Try
oMainQueryR = "SELECT NameID, Address, Ocupation FROM Employees Where Name= :Name"
Dim cmdSQLite As SQLite.SQLiteCommand = connection.CreateCommand()
With cmdSQLite
.CommandType = CommandType.Text
.CommandText = oMainQueryR
.Parameters.Add(":Name", SqlDbType.VarChar)
End With
'Prevent duplicate selects by using a dictionary
Dim NameInalready As New Dictionary(Of String, String)
For Each row As DataRow In TheLIST.Rows
If NameInalready.ContainsKey(row.Item("Name")) Then
Else
NameInalready.Add(row.Item("Name"), "")
cmdSQLite.Parameters(":Name").Value = row.Item("Name")
cmdSQLite.ExecuteNonQuery()
End If
Next
sqliteTran.Commit()
Catch ex As Exception
End Try
End Using
First, you don't need a transaction because you aren't updating the database.
Second, depending on the possible number of Names in TheLIST, it might be worthwhile for you to change the name selector to IN (i.e. SELECT * FROM Employees WHERE Name IN ('name1', 'name2'). However, if you expect more than about 10, this is probably not worth trouble.
Finally, you need to create a new DataTable to hold the results. Then you need to create a DataAdapter passing cmdSqlLite as the constructor parameter. And finally, replace your ExecuteNonQuery with DataAdapter.Fill(DataTable).
For example (after Dim cmdSQLite):
Dim oDataTable As New DataTable("Employees")
Dim oAdapter As New SqliteDataAdapter(cmdSQLite)
and replacing the ExecuteNonQuery line with:
oAdapter.Fill(oDataTable)
I will qualify this code by saying it may need some tweaks. I only work with class objects and collections, so my preference would have actually been to load a collection of Employee class instances.
I would have done that by replacing ExecuteNonQuery with ExecuteReader and then the loading the read data into a new class instance. This type of approach resolves various issues with serializing the data across service boundaries (i.e. Xml for web services) and also lets you embed business logic, if needed, into the classes.
I'm trying to solve a problem regarding types of list. First of all I have a stored procedure in my DB which does a select of a single column and I try to proceed it in my app in VB. By making a method function I declared a DataTable that loads through the SqlCommand(with the CloseConnection behavior). After that I publicly declared a List(Of String) which needs to be populated with the rows/items from the stored procedure that is on the way. Below is my snippet of the code:
Dim dt As New DataTable()
Try
If conn.State = ConnectionState.Open Then
conn.Close()
Else
conn.Open()
Dim cmd = New SqlCommand("LoadCodes", conn)
cmd.CommandType = CommandType.StoredProcedure
dt.Load(cmd.ExecuteReader(CommandBehavior.CloseConnection))
Dim collection As New List(Of DataRow)
collection = dt.AsEnumerable.ToList
LPrefix = collection.Cast(Of String)()
End If
Catch ex As Exception
MsgBox(ex.Message + vbCritical)
End Try
It's LPrefix = collection.Cast(Of String)() where I get an exception error telling me that I can't really convert it. The old fashion way is to iterate with for/for each loop but that's not what I want for best use of performance especially if the list will have thousands of rows from a single column. So basically I want to insert those items from that DataTable to the List(Of String) without using For/For Each loop.
Running on Visual Studio 2010 Ultimate, .NET Framework 4.0.
You don't need your collection at all. Using LINQ, you can extract the first column directly out of your data table:
dt.Load(cmd.ExecuteReader(CommandBehavior.CloseConnection))
LPrefix = (From row In dt.AsEnumerable()
Select row.Field(Of String)(0)).ToList()
Of course, this might use a loop internally, but since you want to copy each value into a list of strings, you cannot do it without looping through the data rows.
Another alternative would be to use an IEnumerable(Of String) instead of a List(Of String):
dt.Load(cmd.ExecuteReader(CommandBehavior.CloseConnection))
Dim LPrefixNew As IEnumerable(Of String) = _
From row In dt.AsEnumerable()
Select row.Field(Of String)(0)
You can iterate through IEnumerable just as you would through a list, but evaluation is lazy: As long as you don't access the elements, the DataTable is not traversed. So, accessing this IEnumerable is like reading the elements directly from the DataTable, just in a more convenient way.
Another word of advice: You should not try to reason about performance until you have measured it. For example, your line collection = dt.AsEnumerable.ToList probably already loops through your entire DataTable and copies each DataRow reference into a List of DataRows; so, with this line, you already have the performance penalty that you are trying to avoid.
So, don't automatically assume that some For loop is always slower than some single statement. Measure it, then optimize.
Assuming your DataRow only has one column you just need to instruct ConvertAll to cast it:
LPrefix = collection.ConvertAll(Function(x) x[0].ToString)
Thanks to Binary Worrier for c#-2-vb translation!