I'm trying to Autocomplete City names from a huge sql table. My code below work but its very slow and sometimes it freezes because I got a lot repeated suggestions. any way to filter all this repeated string to make it faster ? thanks
Public Function GetCompletionList(ByVal prefixText As String, ByVal count As Integer) As String()
Dim strCn As String = "Data Source=sqlserver\sqlexpress;Initial Catalog=zip;User ID=sa;Password=xxx"
cn.ConnectionString = strCn
Dim cmd As New SqlClient.SqlCommand
cmd.Connection = cn
cmd.CommandType = CommandType.Text
cmd.CommandText = "select * from zip_code Where City like #myParameter+'%'"
cmd.Parameters.AddWithValue("#myParameter", prefixText)
Try
cn.Open()
cmd.ExecuteNonQuery()
Dim da As New SqlDataAdapter(cmd)
Dim dt As New DataTable()
da.Fill(ds)
Catch ex As Exception
Finally
cn.Close()
End Try
dt = ds.Tables(0)
Dim txtItems As New List(Of String)()
Dim dbValues As String
For Each row As DataRow In dt.Rows
dbValues = row("City").ToString()
dbValues = dbValues.ToLower()
txtItems.Add(dbValues)
Next
Return txtItems.ToArray
You are executing your SQL twice, once during ExecuteNonQuery, second time during Fill.
You are not using IDisposable objects correctly.
You return all columns.
If you have a control for display, check if it will accept Rows (Dataset?) property directly. Don't copy.
UPDATE
Your connection, command and other objects implement an IDisposable interface. So they should be placed in a using block:
Using { resourcelist | resourceexpression }
[ statements ]
End Using
Then you don't have to worry about closing and disposing a database connection.
UPDATE 2
Your code has thread safety issues, the same connection must not be shared by two different threads. EVER. Two consecutive Fill request and one will close the database connection before the other can finish.
Related
I have two connections types to be used in my app. One is SQL Server, using the SqlClient.Connection type. The other one uses the OleDb.Connection type.
The question is, when using a DataAdapter, DataReader, and Command, how can I use one reference for each with both connections?
As an example, I want to use a reader like this:
Dim MyReader As OleDb.OleDbDataReader
to check my data with an OleDbConnection, and then use same reader to check data from the second SqlClient connection. That is, I want to do something like this (pseudocode):
Dim con
Dim MyReader
con = oledb.connection
MyReader = mymethod(con)
con = sql.sqlclient.conection
MyReader = mymethod2(con)
How can I do this in real code?
I need help in how to declare data components for two different connection types inside the same method or function.
You should declare multiple variables. It's really not a big deal to do so.
But, if you really want to do this (again: not the best idea) one thing you can keep in mind is these objects all inherit from a common set of types in the System.Data.Common namespace. So it possible to write code like this:
Dim con As System.Data.Common.DbConnection = New OleDbConnection("connection string here")
Dim cmd As System.Data.Common.DbCommand = New OleDbCommand("SELECT * ... ", con)
con.Open()
Dim rdr As System.Data.Common.DbDataReader = con.ExecuteReader()
While rdr.Read()
' ...
End While
con.Close()
con = New SqlClient.SqlConnection("connection string here")
cmd = New SqlClient.SqlCommand("SELECT * ...", con)
con.Open()
rdr = cmd.ExecuteReader()
While rdr.Read()
' ...
End While
But again: you really are better off using separate variables.
Trying to update an old VB6 app to VB.Net. I am having trouble with syntax, I think. In any case it is a simple matter of inserting a new record to the autolog table. (code below).
I would like to ask something else that is often not documented too. It seems that I have to use command builders and so on - is there no way I can simply use an SQL statement and execute it against the background table? The tables are in Access while I am developing but will be scaled up on the final release of the software.
I have altered my code to the following by making use of the error suggestions at the foot of mygui.
It now looks like this and the only thing is that it is throwing a logic error at me which is that every end function must have a preceding "function". Perhaps I am being a little bit dim
Function MAutolog(ByVal Action As String) As Boolean
Dim SQL = "Insert Into Autolog (Action) Values (#Action)"
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\PC User\Documents\Freightmaster\resources\freightmaster.accdb"),
cmd As New OleDb.OleDbCommand(SQL, con)
cmd.Parameters.Add("#Action", OleDb.OleDbType.VarChar).Value = Action
con.Open()
cmd.ExecuteNonQuery()
End Using
MAutolog = True
End Function
I would like to thank you for your help in advance. I can not tell you how much I will appreciate it.
Code
Module ModFunctions
Function MAutolog(ByVal UserID As Long, ByVal Action As String) As Boolean
Dim dbprovider As String
Dim dbsource As String
Dim mydocumentsfolder As String
Dim fulldatabasepath As String
Dim TheDatabase As String
Dim SQL As String
Dim DS As New DataSet
Dim da As OleDb.OleDbDataAdapter
Dim con As New OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\PC User\Documents\Freightmaster\resources\freightmaster.accdb")
con.Open()
'----------------------------
SQL = "Select * from Autolog"
da = New OleDb.OleDbDataAdapter(SQL, con)
da.Fill(DS, "Log")
con.Close()
Dim CB As New OleDb.OleDbCommandBuilder(da)
Dim DSNEWROW As DataRow
DSNEWROW = DS.Tables("Log").NewRow()
DSNEWROW.Item("UserID") = UserID
DSNEWROW.Item("Action") = Action
DS.Tables("log").Rows.Add(DSNEWROW)
da.Update(DS, "log")
MAutolog = True
End function
Database objects like Connection and Command use unmanaged code and need their Dispose methods to release these resources. Either call this method on these objects or use Using...End Using blocks which will do this for you even if there is an error. In this code, both the Connection and Command are included in the Using block by separating them be a comma.
By Val is the default so is not necessary.
Always use parameters to avoid sql injection. Using values directly from user input can allow malicious code to be executed on your database. The value of a parameter is not considered as executable code by the database.
OleDb does not care about parameter names. You could just as easily use ? in the sql statement. I use names for readability. You do need some sort of name to add the parameter. OleDb considers the position of the parameter in the sql statement. The position must match the order that the parameters are added to the parameters collection.
This is the code for the Insert if UserID in an auto-number field. You do not provide a value for auto-number fields. The database will handle that.
Function MAutolog(Action As String) As Boolean
Dim SQL = "Insert Into Autolog (Action) Values (#Action)"
Using con As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\PC User\Documents\Freightmaster\resources\freightmaster.accdb"),
cmd As New OleDbCommand(SQL, con)
cmd.Parameters.Add("#Action", OleDbType.VarChar).Value = Action
con.Open()
cmd.ExecuteNonQuery()
End Using
MAutolog = True
End Function
If UserID is not auto-number
Function MAutolog(UserID As Long, Action As String) As Boolean
Dim SQL = "Insert Into Autolog (UserID, Action) Values (#UserID, #Action)"
Using con As New OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\PC User\Documents\Freightmaster\resources\freightmaster.accdb"),
cmd As New OleDbCommand(SQL, con)
cmd.Parameters.Add("#UserID", OleDbType.Integer).Value = UserID
cmd.Parameters.Add("#Action", OleDbType.VarChar).Value = Action
con.Open()
cmd.ExecuteNonQuery()
End Using
MAutolog = True
End Function
I have a public class called dbOPS that has some subs and functions like:
Public Function getSqlReader(ByVal sql As String) As SqlDataReader
Dim cmd As New SqlCommand(sql, getConn)
cmd.CommandTimeout = 360
Dim dr As SqlDataReader = cmd.ExecuteReader(Data.CommandBehavior.CloseConnection)
Return dr
End Function
Public Function getSqlScalar(ByVal sql As String)
Dim cmd As New SqlCommand(sql, getConn)
cmd.CommandTimeout = 360
Dim cnt = cmd.ExecuteScalar
closeCX()
Return cnt
End Function
Public Sub ExecuteSql(ByVal sql As String)
Dim cmd As New SqlCommand(sql, getConn)
cmd.CommandTimeout = 360
cmd.ExecuteNonQuery()
closeCX()
End Sub
I then use the following command once per page and use the db variable many (many) times throughout the page:
Dim db as new dbOPS
Recently, I have started getting many errors
ExecuteScalar requires an open and available connection. the connection's current state is connecting
Is this the cause?
Is there any way around it without rewriting every page and every command to open its own connection?
Thanks
It's probably best to detect the connection and reopen them just in case it is not open prior to executing the command.
If (cmd.Connection.State != ConnectionState.Open) Then
cmd.Connection.Open()
Do this as part of your helper methods.
I have 2 data sources from different source types, like:
Dim connSql As String = "Data Source=sql_src;Initial Catalog=my_db;Persist Security Info=True;User ID=usr;Password=pwd;"
Dim connOle As String = "Provider=IBMDA400;Data source=src;User Id=usr;Password=pwd"
dim qrySql as String = "Select uniqueID, name From tblSql"
dim qryOle as String = "Select name, ID From tblOle"
I place them into DataTables using functions like this (mostly for reference):
Public Shared Function sqlQryDT(qry As String, conn As String) As DataTable
Dim dt As New DataTable
Dim sqlconn As New SqlClient.SqlConnection(conn)
sqlconn.Open()
Dim adapter As New SqlClient.SqlDataAdapter(qry, sqlconn)
Try
adapter.Fill(dt)
Catch ex As Exception
Finally
sqlconn.Close()
End Try
Return dt
End Function
Public Shared Function oleQryDT(qry As String, conn As String) As DataTable
Dim dt As New DataTable
Dim cn As New OleDb.OleDbConnection(conn)
Dim cmd As New OleDb.OleDbCommand("", cn)
Dim da As New OleDb.OleDbDataAdapter(cmd)
cmd.CommandText = qry
Try
cn.Open()
da.Fill(dt)
Catch ex As Exception
Finally
cn.Close()
End Try
Return dt
End Function
Dim dtSql as DataTable = sqlQryDT(qrySql, connSQL)
Dim dtOle as DataTable = oleQryDT(qryOle , connOle)
My goal is to have a DataTable consisting of uniqueID,name,ID
(Edit) If I could do an SQL query it would look like SELECT * FROM dtSql JOIN dtOle ON dtSql.name = dtOle.name
I have tried using a DataRelation by placing the tables into a DataSet and adding a relationship on name, but since names may not be unique, this fails.
I have also tried using LINQ, but that always returns IEnumerable(System.Collections.Generic) and I can't find an easy way to place the contents into a DataTable, except by iterating through every item. And, the code is messy when there are a large number of columns.
I feel like there should be a way to do this without using a For Each loop
I looked at these question, but they didn't fully help me.
How to inner join two already filled DataTables in VB.NET
Merging 2 data tables in vb.net
I am new to vb.net and I am trying to query a database and print out the records in the row to the console window. I got it to work, but I have a feeling that there is a more concise way to do this. One thing that I am sure is wrong is that I had to convert the dataset to a datatable to be able to retrieve the values. Is that correct? Could you take a look at the code below (especially the for loop) and let me know what I can improve upon?
Thanks!
Module Module1
Sub Main()
Dim constring As String = "Data Source=C:\Users\test\Desktop\MyDatabase1.sdf"
Dim conn As New SqlCeConnection(constring)
Dim cmd As New SqlCeCommand("SELECT * FROM ACCOUNT")
Dim adapter As New SqlCeDataAdapter
Dim ds As New DataSet()
Try
conn.Open()
cmd.Connection = conn
adapter.SelectCommand = cmd
adapter.Fill(ds, "testds")
cmd.Dispose()
adapter.Dispose()
conn.Close()
Dim dt As DataTable = ds.Tables.Item("testds")
Dim row As DataRow
Dim count As Integer = dt.Columns.Count()
For Each row In dt.Rows
Dim i As Integer = 0
While i <= count - 1
Console.Write(row(i))
i += 1
End While
Console.WriteLine(Environment.NewLine())
Next
Catch ex As Exception
Console.WriteLine("There was an error")
Console.WriteLine(ex)
End Try
Console.ReadLine()
End Sub
End Module
Here is how I would rewrite this for a few reasons:
1) You should always use Using statements with disposable objects to ensure they are correctly cleaned up. You had a good start with the dispose commands, but this way is safer.
2) It is more efficient to use ExecuteReader than loading everything into a dataset.
3) Your try/catch statement should include object creation as well as execution.
Finally, in response to your question about datasets and datatables, that code was absolutely correct: a dataset consists of zero or more datatables, so you were just extracting the existing datatable from the dataset.
Try
Dim constring As String = "Data Source=C:\Users\test\Desktop\MyDatabase1.sdf"
Using conn As New SqlCeConnection(constring)
conn.Open()
Using cmd As New SqlCeCommand("SELECT * FROM ACCOUNT", conn)
Dim reader As SqlCeDataReader
reader = cmd.ExecuteReader()
Do While reader.Read
For i As Integer = 0 To reader.FieldCount - 1
Console.Write(reader.GetString(i))
Next
Console.WriteLine(Environment.NewLine())
Loop
End Using
End Using
Catch ex As Exception
Console.WriteLine("There was an error")
Console.WriteLine(ex)
End Try
Console.ReadLine()
End Sub
One last note: since you are just printing to the console, it doesn't matter as much, but whenever you deal with a lot of strings, especially those that are to be concatenated, you should always consider using System.Text.StringBuilder.
Here is an example rewrite of the loop that prints to the console using stringbuilder (builds the string in memory, then dumps it to the console; I have also added the field name for good measure):
Dim sbOutput As New System.Text.StringBuilder(500)
For i As Integer = 0 To reader.FieldCount - 1
If sbOutput.Length <> 0 Then
sbOutput.Append("; ")
End If
sbOutput.Append(reader.GetName(i)).Append("=").Append(reader.GetString(i))
Next
sbOutput.AppendLine()
Console.Write(sbOutput.ToString)