I want to find the text in textbox in my database. I wrote the code below. It finds numbers well, but when I want to find strings it gives a runtime error: invalid column name for example aaa, but aaa exists in column1 in my table.
What do you think about the problem?
cmd = New SqlCommand("select * from tbl where column1=" + TextBox1.Text)
cmd.CommandType = CommandType.Text
cmd.Connection = cnn
dad.SelectCommand = cmd
cmd.ExecuteNonQuery()
dad.Fill(ds)
dgv.DataSource = ds.Tables(0)
That's because the sql statement you send is not delimiting the TextBox1.Text value so you end up with this sql:
select * from tbl where column1 = aaa
and SQL Server treats aaa as a column name.
Regardless of that, you should be using a SqlParameter to avoid sql injection attacks:
cmd = New SqlCommand("select * from tbl where column1=#value")
cmd.CommandType = CommandType.Text
cmd.Paramaters.AddWithValue("#value", TextBox1.Text)
VB is not my primary language, so the syntax might be a little off, but you should be able to make it work.
Adritt is right, you must enclose the text to find within single quotes and, provided that very text doesn't contains single quotes, all is well - Apart for the risk of SQL attacks.
That being said, you are using an outdated, obsolete way of coding your app against the database.
You should definitively have a deep look at LINQ technology where:
You have no connection to open or close: its automatic
You don't have to cope with quotes, crlf and commas
You do not risk SQL attacks: queries are parameterised by the LINQ engine
You will benefit from intellisense againts the database objects: tables, views, columns
You get a straightforward result to use as the datasource!
For INSERT and UPDATE statements transactions are automatically enabled.
Example:
using ctx as new dataContext1
dim result = from r in ctx.tbl
where r.column1 = textBox1.text
dgv.datasource = result.tolist
end using
Intellisense:
When you type "ctx.", you are presented with the list of available tables!
When you type "r." you are presented with the list of column the table (or vieww) contains!
LINQ is not difficult to learn and you'll find tons of examples to help you, here and there on the web.
Last but not least, you can use the LINQ SQL-like syntax to query XML data, CSV files, Excel spreadsheets and even the controls in your form, or the HTML DOM document in ASP.NET!
Related
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'm curious to know a proper way to insert text strings into a database regardless of what characters are contained within the string. What I'm getting at is if I have a string for example that contains single quotes or any other character that is reserved as a 'special' SQL character.
The issue specifically that I'm dealing with is that I don't have control over the possible 'Text' that is being inserted into my database as they text is generated by my application.
One example of where my application fails to insert properly is when there's an error message that happens to contain single quotes. Single quotes are used by SQL statements insert text of course and so I can't insert text that also contains single quotes (outside of using ascii value char(##) function). The issue I'm dealing with is that I'm setting the output of my application to a string variable to then be inserted into my database so I can log activity whether that be standard output or catching errors.
How do I simply INSERT what's contained in my string variable while avoiding all of the SQL Special characters?
Do I need to manually account for all of the SQL Special characters and replace them in my string prior to insert? This sounds like a hit or miss and I'm hoping that there's something already built to accommodate this situation.
Sample Pseudo Code to get the point across:
Let's say an error occurred within the app and it needs to be logged. The error string could be:
Error String: "Error in function calculateStats() parameter 'pBoolStatCheck' is Null"
Now I assign to my string variable within my app and build up the SQL Insert string.
var insertString = "Error in function calculateStats() parameter 'pBoolStatCheck' is Null"
INSERT INTO outputLog(outputLogText)
VALUES ('insertString'); --This will Fail
--Fails due to the variable 'insertString' containing single quotes.
INSERT INTO outputLog(outputLogText)
VALUES ('Error in function calculateStats() parameter 'pBoolStatCheck' is Null');
In closing - since I have no control over the text that could be created by my application how do I account for all of the possible characters that could break my insert?
The code my current application encountering this issue is written in Visual Basic. The database I'm working with is SQLite.
The final solution based on answers received by this post:
Public Sub saveOutputLog(pTextOutput, pTextColor, pNumNewLines, plogType, pMethodSub)
Dim strTableName As String = "outputLog"
Dim sqlInsert As String = "INSERT INTO " & strTableName & "(" &
"outputLog, logColor, numNewLines, logType, method" &
") VALUES (#outputLog, #logColor, #numNewLines, #logType, #method);"
Try
'Open the Database
outputLogDBConn.Open()
'Create/Use a command object via the connection object to insert data into the outputLog table
Using cmd = outputLogDBConn.CreateCommand()
cmd.CommandType = CommandType.Text
cmd.CommandText = sqlInsert
cmd.Parameters.AddWithValue("#outputLog", pTextOutput)
cmd.Parameters.AddWithValue("#logColor", pTextColor)
cmd.Parameters.AddWithValue("#numNewLines", pNumNewLines)
cmd.Parameters.AddWithValue("#logType", plogType)
cmd.Parameters.AddWithValue("#method", pMethodSub)
'Execute the command using above Insert and added Parameters.
cmd.ExecuteNonQuery()
End Using 'Using outputLogDBComm
outputLogDBConn.Close()
Catch ex As Exception
outputLogDBConn.Close()
End Try
End Sub
This problem is very similar to the problem of preventing SQL Injection vulnerabilities in your code. Queries are very easy to break, and while yours breaks in a way that is harmless and annoying, these can be taken to levels where certain inputs can completely destroy your database!
One of the best ways to approach this is by using parameterized queries. This approach is pretty simple; you write the query first with 'placeholders' for the parameters you will send. Once you are ready in your program you can then 'bind' those parameters to the placeholders.
It would look something like the following:
Dim command = New SqlCommand("INSERT INTO outputLog(outputLogText) VALUES (#stringToInsert)", connection);
.
.
.
code
.
.
.
command.Parameters.AddWithValue("#stringToInsert", errorMessage)
.
.
.
execute query
In the above you see that #stringToInsert is the placeholder which is only bound at a later time. It doesn't matter what the variable errorMessage contains, since it will not cause the query to function in a way where the input causes it to potentially break.
There are a lot of resources on this:
https://learn.microsoft.com/en-us/dotnet/api/system.data.sqlclient.sqlcommand.prepare?view=netframework-4.7.2
Database objects like connections not only need to be closed but also disposed. A Using block will ensure this will happen even if there is an error.
The .Add is better than .AddWithValue for a number of reasons. See https://blogs.msmvps.com/jcoehoorn/blog/2014/05/12/can-we-stop-using-addwithvalue-already/ and http://www.dbdelta.com/addwithvalue-is-evil/
The parameters of .Add are the name of the parameter, the datatype in the database and optionally the size of the field. You will need to check the database for the last 2.
Open the connection at the last minute befor the execute.
If you are using OleDb with Access, you need to make sure the parameters are added in the same order as they appear in the sql statement.
Using cn As New SqlConnection("Your connection string")
Using cmd As New SqlCommand("INSERT INTO outputLog(outputLogText) VALUES (#outputLogText);", cn)
cmd.Parameters.Add("#outputLogText", SqlDbType.VarChar, 100).Value = TextBox1.Text
cn.Open()
cmd.ExecuteNonQuery()
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.
First time poster - medium length reader. I'm an entry level programmer, currently working on passing a SQL Stored Procedure some information that might contain a single quote (').
In the past, we've attempted to just use a .Replace("'","''") when passing this information, but recently, we've run into some issues with returning data and having the set changes and replaces in about 20 places (corporate, woo!).
I've been looking at using SQL Parameters to not have to worry about these buggers: ', but cannot see/understand the difference in my below code. The first block was the original working version. The second is my attempt at introducing #paras.
SQL is being passed through ByVal as a String
Previous Code:
Dim dbConnection As New SqlConnection(ConnectionString)
Dim dbCommand As New SqlCommand(SQL, dbConnection)
MsgBox(dbCommand.CommandText.ToString) //Returns proper procedure/paras
dbCommand.CommandTimeout = CommandTimeout
dbConnection.Open()
dbCommand.ExecuteNonQuery()
Code with SQL Parameters:
Dim dbConnection As New SqlConnection(ConnectionString)
Dim dbCommand As New SqlCommand("#SQL", dbConnection)
dbCommand.Parameters.Add("#SQL", SqlDbType.VarChar).Value = SQL
MsgBox(dbCommand.CommandText.ToString) //Returns "#SQL"
dbCommand.CommandTimeout = CommandTimeout
dbConnection.Open()
dbCommand.ExecuteNonQuery()
I feel the second block should be returning the same information. A MsgBox from the first block will return the proper SQL. The second however, just returns "#SQL", not the SQL value it seems to assign.
Is there a special way of refreshing the SQL Command?
Am I unable to only declare #SQL and replace it later?
Took a peek around MSDN as well as quite a few searches, leading me here already, with no luck.
Here is how you would make this a parameterized call. Kudos for taking the effort to protect against sql injection!!!
dbCommand.CommandText = "LoginPassword"
dbCommand.CommandType = CommandType.StoredProcedure
dbCommand.Parameters.Add("#userID", SqlDbType.VarChar, 30).Value = userID
dbCommand.Parameters.Add("#Password", SqlDbType.VarChar, 30).Value = password
dbCommand.ExecuteNonQuery()
One thing you need to make sure you do is when you use parameters you should always specify the precision or length. I don't know what yours should be in this case so you will need to adjust as required.
--please forgive me if there is a syntax error. I work with C# but I think I got this correct for vb.net
I am new to this forum, please could you help me get this code to work, when i execute it, it simply does nothing and does not update the DB. If i remove the square brackets it gives an error: "SYNTAX ERROR in UPDATE statement"
Any help appreciated!
Dim connection As OleDbConnection
connection = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=UserDB.accdb;Jet OLEDB:Database;")
connection.Open()
Dim pass As String
pass = txtconfirm.Text
Dim user As String
user = LoginForm.UsernameTextBox.Text
Dim query As String = "UPDATE [Users] SET [Password]= '" & pass & "' WHERE [Username]= '" & user & "';"
Dim command As New OleDbCommand(query, connection)
command.ExecuteNonQuery()
connection.Close()
Given your actual connection string, the database that will be updated is the one in the directory where your application starts. This means that if you work with a WinForms application this folder is \BIN\DEBUG or x86 variant. If there is not error then you could get the return value of the ExecuteNonQuery call to verify if a record has been updated or not
Dim rowsUpdated = command.ExecuteNonQuery()
MessageBox.Show("Record updated count = " & rowsUpdated)
If this value is not zero then your database has been updated and you are looking for changes in the wrong database. Check the one in the BIN\DEBUG folder.
In any case your code has big problems. If your variables user or pass contain a single quote, then your code will crash again because your string concatenation will form an invalid SQL. As usual the only workaround is to use a parameterized query
Dim pass = txtconfirm.Text
Dim user = LoginForm.UsernameTextBox.Text
Dim query As String = "UPDATE [Users] SET [Password]= #p1 WHERE [Username]= #p2"
Using connection = New OleDbConnection("...........")
Using command As New OleDbCommand(query, connection)
connection.Open()
command.Parameters.Add("#p1", OleDbType.VarWChar).Value = pass
command.Parameters.Add("#p2", OleDbType.VarWChar).Value = user
command.ExecuteNonQuery()
End Using
End Using
The parameterized approach has many advantages. Your query text is more readable, there is no misunderstanding between your code and the values expected by your database engine. And while not easy to exploit with MS-Access there is no problem with Sql Injection
I think Steve presents a much better approach for you coding this...
Let me just throw out a few more things:
The reason you can't take those brackets out is some of your column names are reserved words; just FYI.
Since you report "it does nothing..." when you execute, it sounds like you have a valid connection and sql syntax, in which case my next step would be to copy the sql command text while in debug mode, change it to a select and run it in your DB. You should get one result when you do. If not, either your criteria or field contents are not what you think they are...
Just change the Update table SET field-value ... to SELECT * FROM table and leave the WHERE clause as is.