I'm creating a program in Visual Basic for a school project. The program is a very simple tool to aid in the designing of a guitar. Users must login to use the program. I have setup an Access database to store all the data on the users and their designs. At the moment the login system uses SQL queries to find the inputted username in the database:
Private Sub cmd_login_Click(sender As Object, e As EventArgs) Handles cmd_login.Click
Call Login_Validation()
provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
'access database location
dataFile = "C:\Users\Jackson\Desktop\Guitar Builder\Guitar Builder.accdb"
connString = provider & dataFile
myConnection.ConnectionString = connString
'the query:
myConnection.Open()
Dim cmd As OleDbCommand = New OleDbCommand("SELECT * FROM [Users] WHERE [Username] = '" & usn_box_login.Text & "' AND [Password] = '" & psw_box_login.Text & "'", myConnection)
Dim dr As OleDbDataReader = cmd.ExecuteReader
' userExists is set to true if the username user is found or false if it is not found
Dim userExists As Boolean = False
'if found:
While dr.Read
userExists = True
FullName = dr("Full Name").ToString
userName = dr("Username").ToString
End While
'checking the result
If userExists = True Then
Me.Hide()
Dashboard.Show()
Dashboard.lbl_name.Text = FullName
Dashboard.lbl_username.Text = userName
Else
MsgBox("Sorry, username or password not found", MsgBoxStyle.OkOnly, "Invalid Login")
End If
usn_box_login.Clear()
psw_box_login.Clear()
myConnection.Close()
End Sub
This works, however there must be a binary search in the program for it to pass the school's assessment. What is the easiest way to implement binary search to find the username?
Thank you in advance.
You can't. One of the advantages of using a DBMS like Access (or SQL Server, or SQLite, etc) is to abstract away the details of how data is retrieved and looked-up.
(Most modern database systems use special index structures for quick lookup, such as B-trees (B-trees are not Binary-search trees btw)
If the requirement is to use binary-search to find something, you need to not use something that will do it for you.
As this is for a programming exercise to demonstrate a working knowledge of data structures, I think you should remove Access completely and store data in a simple flat-file, load it all into memory when your program starts, then use your algorithms and structures to work with the data, before spitting it out to the flat-file store when your user clicks the Save button.
Note that I'm guessing using .NET's Array.BinarySearch is also probably cheating.
Other tips:
Don't store passwords in plain-text. They should not be encrypted either. Instead they should be hashed (and preferably salted).
Don't generate SQL using string concatenation. Use parameters instead. (Your code is vulnerable to SQL injection: if you put the text Baba O'Reilly in your textboxes your program will crash.
You should dispose of all your IDisposable objects correctly, ideally using a Using statement.
Run FxCop (Visual Studio Code Analysis) as part of your build process to catch other issues. Choose the "All Rules" setting.
The above bullet-points might sound like nit-picking, but I believe it's important to get into good habits early. The last thing an employer needs is a new hire who added significant vulnerabilities just because they never got used to doing things correctly.
I have taken your advice and removed Microsoft Access completely. I am now using my own record structure within the program.
Related
Dim cat As New Catalog()
Dim con As New OleDbConnection()
Dim cmd As New OleDbCommand
Dim ds1 As New DataSet
Dim conn As ADODB.Connection
' Open the Access database.
conn = New Connection
conn.ConnectionString =
"Provider=Microsoft.Jet.OLEDB.4.0;" &
"Data Source=" + openExcel + "\Test" + ".mdb; Persist Security Info=False"
con.ConnectionString =
"Provider=Microsoft.Jet.OLEDB.4.0;" &
"Data Source=" + openExcel + "\Test" + ".mdb; Persist Security Info=False"
conn.Open()
xlWorkSheet1.Columns(5).Insert
Dim cellValue As String = ""
Dim newValue As String = ""
Dim sh1 As String = ""
Dim qty As String = ""
Dim matchText As String = ""
Dim sql As String = ""
con.Open()
sh1 = LTrim$(xlWorkSheet1.Cells(i, 1).Text)
sql = "SELECT Num_ber, Q_ty FROM good WHERE Na_me LIKE 'staff%' And Ty_pe = 'ORD'"
Dim cmd As New OleDbCommand(sql, con)
Dim myReader As OleDbDataReader = cmd.ExecuteReader()
conn.Execute(sql)
myReader = cmd.ExecuteReader() ' HERE'S THE PROBLEM
xlWorkSheet1.Cells(1, 5) = myReader.GetString(0)
xlWorkSheet1.Cells(1, 11) = myReader.GetString(1)
myReader.Close()
conn.Close()
conn = Nothing
**I wanted to retrieve a specific value from mdb and then write it to excel.
Here's my code, I got this error so many times and I can't find it out. Can anybody help me? Thanks.**
[1]: https://i.stack.imgur.com/6Fuvg.png
Ok, you first have to decide when usng .net what "provider" you are going to use, AND THEN decide what kind of data objects you want to use.
You can use a oracle provider, a sql server provider, or in this case, since we using Access, then we can use EITHER oleDB, or ODBC. Either choice is fine. Most use oleDB providers for Access, but often ODBC is a good choice, especially if down the road you plane to swap out Access for say SQL server.
What the above means in plain English?
You don't want to adopt the external ADODB code and library. That code is NOT .net, and thus you REALLY but REALLY do not want to write your .net code that way. ADODB was written LONG before .net, and is what we call un-managed code (non .net). I strong, but strong suggest you do NOT add a reference to ADODB to your project, and I beyond strong recommend you avoid introduction of a non .net library for doing this!!! We certainly can adopt the oleDB provider in .net, but we will NOT have a direct reference to JET/ACE (the access database engine) in our applcation. As noted, there are some exceptions to this suggesting, but they don't apply to you and here.
Next up:
The design pattern in .net is to create the connection, get the data, and CLOSE the connection. This "pattern" will then be 100% sure that the data base is always closed, and you NEVER have to worry about if the connection is open, closed, or even if you forgot to close the connection!!! So, do this correct, and some "open" connection will never bite you, or will you have to worry about this issue.
You can in some operations keep the connection open for performance, but lets learn to walk before we run so to speak.
next up:
We certainly do NOT want to place and have connection strings all over in our code. Not only is this going to wear out your keyboard, but if you ever need to change the connection, then you going to have to hunt down all that code.
Best to let Visual Studio save that connection in ONE location, and MORE important MANAGE this for you!!!
Next up:
Do you ONLY need to work with mdb files, or do you plan/need to work with accDB files? This is a HUGE issue, and one that you cannot ignore.
next up:
Are you going to use the x32 bit version of the Access database system, or the x64 bit version?
Since your example posted code uses JET (access data engine for mdb files ONLY x32 bit version)?
Then this ALSO means you MUST (and I repeat MUST) force your .net project to run as x32 bits. You cannot use "any cpu", and you cannot use x64 bits, you MUST choose x86 bit size for your .net project. Failure to do so will result in the project not working.
Ok, with the above information?
First up, force/set/be 100% sure your project is set to run as x32 bits.
That setting is this one:
and remove the reference you have to ADO if you created one.
Ok,
next up:
Create the connection to the database.
Project ->properties.
This here:
And then:
and then
Now, you can browse, and select the access mdb file.
But, you MUST not skip the next step - you have to choose JET (older, mdb files), or choose the newer ACE (for accDB format files).
So, this:
now this:
As noted, you choose JET or ACE here.
now, we have this and you can use test connection.
BUT BE VERY careful!!!!
If you are using vs2022, then keep in mind vs2022 is the FIRST version of VS that is now x64 bits. As a result, vs can't pass the test connection!!! Your connection is in fact ok, but will fail with vs2022.
If you using a previous version of VS (before 2022), then the test connection button should work. and you see this:
Ok, now that we have a valid working conneciton setup, we can now write code, and we will NOT use ADODB!!!!
The typical code pattern to read and load a data table (like a access VBA recordset) will be like this:
Now, I became RATHER tired of writing that same using block over and over. So, in a global module, I have this code now:
Public Function MyRst(strSQL As String) As DataTable
Dim rstData As New DataTable
Using conn As New OleDbConnection(My.Settings.AccessDB)
Using cmdSQL As New OleDbCommand(strSQL, conn)
conn.Open()
rstData.Load(cmdSQL.ExecuteReader)
End Using
End Using
Return rstData
End Function
So, now with the above handy dandy helper routine?
Your code becomes this:
Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
Dim Sql As String =
"SELECT Num_ber, Q_ty FROM good WHERE Na_me LIKE 'staff%' And Ty_pe = 'ORD'"
Dim rstData As DataTable = MyRst(Sql)
Debug.Print("Na_me is " & rstData.Rows(0).Item("Na_me"))
End Sub
Or, display all return rows from that data table
Debug.Print("Na_me is " & rstData.Rows(0).Item("Na_me"))
For Each OneRow As DataRow In rstData.Rows
Debug.Print("na_me = " & OneRow("Na_me"))
Next
So, you really don't need (or want) a reader anyway. Just load the results into a nice clean, easy to use data table, and from that you can loop the table, grab rows, or do whatever you want.
I have a list of Users Names in ComboBox and Some TextBoxes. When ComboBox text changes (i.e I select some username from ComboBox), The TextBoxes are filled with user details from the database.
I have code to achieve this in SQL Database. But these queries are not working with MsAccess database.
MysqlConn = New MySqlConnection
Mysql.ConnectionString = "server=localhost;user=root;password=root;database=database"
Dim READER As MySqlDataReader
Try
MysqlConn.open()
Dim Query As String
Query("select * from database.usernames where name='" & ComboBox1.Text & "'")
Command = New MySqlCommand(Query, MysqlConn)
READER = Command.ExecuteReader
While READER.Read
TextBox1.Text = READER.GetString("name")
End While
End Try
Here is my answer. Please don't get overwhelmed by it. ;)
Broken code
First of all, as I see it, the code you provided cannot work at all, because:
your Query variable is initialized in an invalid (or at least a very exotic) way. You probably want to use something like:
Dim Query As String
Query = "select * from database.usernames where name='" & ComboBox1.Text & "'"
or in a single line:
Dim Query As String = "select * from database.usernames where name='" & ComboBox1.Text & "'"
you try to assign the connection string to the ConnectionString property of a nonexistent Mysql variable. Or the variable exists because it is declared somewhere else, which might be a bug in your code snippet here. But I assume you want to assign the connection string to the MysqlConn.ConnectionString property instead.
you have not declared the MysqlConn and Command variables anywhere. You only just assign to them. (I will simply assume you have declared the variables correctly somewhere else in your code...)
the IDataRecord interface does not provide a GetString(name As String) method overload. So unless you have defined a custom extension method for it, you probably need to use the IDataRecord.GetOrdinal(name As String) method as well, or use the column index instead of the column name.
Anyway, the code you provided uses MySQL. So I assume that MySQL is the "SQL Database" you are using successfully. And that seems to work, as you say? Well... Hmmm... Then I will simply assume your code snippet is completely correct and works perfectly with MySQL... :/
MS Access vs. MySQL
Using MS Access requires other data access classes (probably the ones in namespace System.Data.OleDb) and another connection string. You could take a look at this ADO.NET OleDb example for MS Access in the Microsoft documentation.
You probably even have to update your SQL query, because every database system uses its own SQL dialect. You might want to consult the Office documentation for that. But your query is quite simple, so perhaps all you have to do to make it work with MS Access is:
remove the database name and use only the table name, and
delimit the name identifier (since it is a reserved keyword in MS Access).
I personally delimit all identifiers in my SQL queries, just to avoid unintended conflicts with reserved keywords. So I would personally use something like this:
select * from [usernames] where [name] = '...'
Additional tips
Also, I would like to provide you some additional (unrelated) tips regarding improving your code:
Use Using-statements with variables of an IDisposable type as much as possible. Those types/classes do not implement that interface if there isn't a good reason for it, so I consider it not unimportant to call Dispose when you are done with such disposable objects (or using a Using statement to call Dispose implicitly).
Use SQL parameters (if possible) to avoid SQL injection vulnerabilities. Look at this StackOverflow question and its answer for an example of how to use SQL parameters with MS Access.
Example
You may take a look at the following code snippet. It might not provide a working example out-of-the-box, but you might get some useful/practical ideas from it:
Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\Data\\database.mdb;User Id=admin;Password="
Dim query As String = "select * from [usernames] where [name] = #Name"
Using conn As New OleDbConnection(connectionString)
Using command As New OleDbCommand(query)
command.Parameters.Add("#Name", OleDbType.VarChar, 50).Value = ComboBox1.Text
conn.Open()
Using reader As OleDbDataReader = command.ExecuteReader
If reader.Read Then
textbox1.Text = reader.GetString(reader.GetOrdinal("name"))
End If
End Using
End Using
End Using
I have created a database that holds 3 values, the ID, UserName, and Score. I need to create a new entry to this database when the save button is clicked. My program needs to create a new row with the Username and score provided by the application.
This is my code to update an existing database:
Private Sub ButtonSaveScore_Click(sender As Object, e As EventArgs) Handles ButtonSaveScore.Click
provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source="
dataFile = "F:\Documents\Class Documents\CSC289 - K6A - Programming Capstone Project\Project\Scoreboard.accdb"
connString = provider & dataFile
myConnection.ConnectionString = connString
Using con As New OleDbConnection(connString),
cmd As New OleDbCommand("UPDATE [Scores] SET [UserName] = ?, [Score] = ? WHERE [ID] = ?", con)
con.Open()
cmd.Parameters.Add("#ID", OleDbType.Char).Value = "NEW"
cmd.Parameters.Add("#UserName", OleDbType.Char).Value = playerName
cmd.Parameters.Add("#Score", OleDbType.Char).Value = wins
cmd.ExecuteNonQuery()
End Using
End Sub
I get
oledb exception was unhandled
It highlights cmd.ExecuteNonQuery() and says data criteria mismatch.
Can someone give me advice to get this working?
You have a couple of issues there. Firstly, at least one of your parameters is the wrong data type. Secondly, your parameters are in the wrong order.
The Jet and ACE OLE DB providers only partially support named parameters, in that they allow you to use names so that your code can be clearer but they ignore the names and just use the positions. That means that you need to add the parameters to your OleDbCommand in the same order as they appear in the SQL code. You're not doing that so you have one issue there, although that's not the direct cause of your error message.
Even if those providers did fully support named parameters though, you're not using names in your SQL code. That means that there would be no way to match up parameters by name anyway, so how did you think that adding them in the wrong order wouldn't be an issue?
Given that all three of your parameters are specified as the same data type though, the incorrect order would not cause the error message you're seeing. If that data type was correct, you'd just find that the wrong data was saved to some of the columns, which would be even worse, i.e. appearing to work but not rather than just failing. You need to make sure that you use the correct OleDbType value for the column you're trying to save to. If your ID column in the database is specified to contain 32-bit numbers then you should be using OleDbType.Integer for the corresponding parameters. I'd also suggest using VarChar rather than Char unless your column is specifically fixed-width, which a Text column in Access is unlikely to be and I'm not sure even can be.
I have been searching for a couple hours, and found several questions, but none of them really explained this in a way I can understand.
I'm programming a game similar to Rock Paper Sissors, except with many more selections, and the possiblity of a tie. I had originally hardcoded all of the possible outcomes, then decided to try a database so I can learn and practice sql as well.
Problem is, I can't figure out for the life of me how to connect to my local database, now that I have set it up and filled it through Visual Studio 2010. I can connect to it through Server Explorer just fine, and I can see it in Solution Explorer. I've tried several things, along the lines of:
Private sqlConn As New SqlConnection("Data Source=(local)|DataDirectory|\Outcomes.sdf;database=Outcomes;Integrated Security=true")
Private sqlConn As New SqlConnection("Data Source=.\SQLEXPRESS; Integrated Security=true")
Dim sqlConn As SqlConnection
sqlConn = New SqlConnection("DataSource=..\..\Outcomes.sdf")
I am relatively new to sql, but know enough through tinkering to build a sql statement and get me the result I want. But I've never connected to a database before. I've looked on MSDN and tried several things I saw on there (everything that looked like what I needed, really) but it still hasn't worked.
If I can connect, I already have my statement set, and have tested it through the database itself. Any help would be wonderful, especially if it's explained in a way I can understand it and use it for later.
Also, if it helps and isn't noticed through my tried code, my db name is Outcomes. I don't know if that is needed or will help, but just in case.
Please visit connection strings here...
It also would have been helpful to know what type of DBMS you are using as well. I noticed you have an .sdf database file, not a DBMS (For ex: MySql, SQL or Oracle). Therefore, your connection string is really going to depend on what you want.
Your issue is here by the way...
Private sqlConn As New SqlConnection("Data Source=(local)|DataDirectory|\Outcomes.sdf;database=Outcomes;Integrated Security=true")
*You cant use the SqlConnection you have because its not supported with the use of .sdf files.
Instead you have to use: System.Data.SqlServerCe 'This is for compact edition
If you would like to know more about this please see here.
Kendra,
Here are the logical Steps you will need to follow to access the database programmatically:
Note: I'm assumming you have the proper SQLExpress | SQL Server Database setup whether local or remote the methods below are identical except for the connection string information.
1) Import the Sql AdoNet Namespace so you can use the proper SQL Server Client Objects & Methods;
a) Imports System.Data.SqlClient
2) Establish a Connection to the database with the ADO Connection Object:
' Create your ADO Connection Object:
Private myConn As SqlConnection
myConn = New SqlConnection("Initial Catalog=OutComes;" & _
"Data Source=localhost;Integrated Security=SSPI;")
Note: This connection string uses integrated security from your windows machine. you could also use standard security where you would need to enter your username and password credentials. Its your choice.
3) Setup Your ADO Command Object to Define your data retrieval query:
'Create a Command object.
Private myCmd As SqlCommand
myCmd = myConn.CreateCommand
myCmd.CommandText = "SELECT FirstName, LastName FROM Employees"
'Open the connection.
myConn.Open()
Note: Subsitute CommandText string for your actual query based upon your own database schema.
4) Read, Fetch, Display Data using the SQLDataReader Object:
Private results As String
Private myReader As SqlDataReader
myReader = myCmd.ExecuteReader()
'Traverse the DataSet and Display in GUi for Example:
Do While myReader.Read()
results = results & myReader.GetString(0) & vbTab & _
myReader.GetString(1) & vbLf
Loop
'Display results.
MsgBox(results)
5) Gracefully Close all Objects Used:
' Close the reader and the database connection.
myReader.Close()
myConn.Close()
Note - You'll need to consult microsoft for further connection string formats, since I don't have enough info. But this should clarify the actual big picture steps for you.
Regards,
Scott
This may have been answered but my search hasn't found what I was looking for.
Basically, I am developing an application which allows the user to build a query at design time, i.e. for users with no prerequisite knowledge of SQL
The application thus far allows the user to select which table(s) from the database they wish to start querying (I won't go into the details of the rest for now)
My confusion is this; I already have the connection to the database in a subroutine which obtains the schema information and filters it to display only the available tables within the database, which then compiles the data into a listbox, here is that sub:
Public Sub getSchemaInfo()
Dim ds As New DataSet
Dim dt As New DataTable
Dim con As New OleDbConnection
Dim strDatabaseLocation As String = Application.StartupPath
Dim da As New OleDbDataAdapter
Dim i As Integer
'ds.Tables.Add(dt)
con.ConnectionString = "Provider=microsoft.jet.oledb.4.0; data source = " & strDatabaseLocation & _
"\EmployeeDepartment.mdb"
'clear listbox of any data first
frmAddTable.lbTables.Items.Clear()
'Try catch block used to handle connection errors gracefully
Try
con.Open()
'Accessing methods to obtain schema information
dt = con.GetOleDbSchemaTable(OleDb.OleDbSchemaGuid.Tables, New Object() _
{Nothing, Nothing, Nothing, "TABLE"})
'loop datatable to store schema information within it
For i = 0 To dt.Rows.Count - 1
'compile lbtables with a list of available tables from the database
frmAddTable.lbTables.Items.Add(dt.Rows(i)!TABLE_NAME.ToString())
Next
Catch ex As Exception
MessageBox.Show(ex.Message.ToString(), "Data Load Error", MessageBoxButtons.OK,
MessageBoxIcon.Exclamation)
End Try
con.Close()
As you can see, at the very top is all the information regarding the connection to the database and loading of the information into the dataset.
My question is this; Whenever I need to gain access to the database and any information within it, will I have to perform all the connection process (oledbconnection, etc..)
or is there I way I can create a class for the connection functions and simply reference them whenever I need to connect?
For example, I now am in the process of creating another sub which gathers the columns, based on the tables chosen in the listbox, and displays it back onto the main form in the relevant checklistbox, again, connecting to the database, therefore would I need to perform all of the connection processes?
Any information would be very useful, thank you!
It is a standard approach to separate your DAL ( Data Access Logic ) from your Business Logic. I would definitely create a separate class for connecting to the database and executing the queries that would bring back the results that you can then either Bind to a control or iterate over inside a loop.
You might even want to look into using EF ( Entity Framework ) or my favorite LINQ to SQL to help in following a standard Design Pattern. By using a framework like EF or L2S you can leverage their ability to cache objects and return back strongly typed objects versus loosely typed. Strongly typed objects give you intelisense and are less prone to common mistakes like misspelling a field from a DataTable.