VB.Net与SQL通讯

Question

I haven't done any serious programming in years, and I don't have much experience manipulating SQL data indirectly anyway, but I'm trying to create a program for my employer and running into confusion. Many of the answers here and college books i have are helpful, but just when I think I understand what's going on, I get lost again, often because people use variables and column names that are identical, leaving it hard to figure out what is going where.

So let's say I have a database called Attendance on SQL server localhost. Inside is a table called employees which consists of the columns: employee_id , name_last , name_first , and points . The first three are varchar and the last is a decimal(2,1) . Using Visual Studio for Visual Basic, I've created a program which contains several textboxes. The user enters the employee id which becomes var_empid when they hit the Load button.

How would I proceed so that the program executes an SQL query which pulls the name_last and name_first from the table where the employee_id matches the var_empid as input by the user and puts that data into the var_last_name and var_first_name variables?

Secondly, if the user entered into other textboxes information that became var_empid , var_last_name , var_first_name and then clicked the Add Employee button, how I would i proceed so that the information added by the user is written to the SQL table?

For clarification, moving data between textboxes and variables isn't the problem. I can do that all day. It's moving the variables between the VB and SQL that is causing me problems. I realize this is basic stuff, but any help would be great.

Answer 1

This is more than what you asked for, because I'm trying to push you into some good practices at the same time:

Public Class Employee
    Public Property ID As String 
    Public Property Points As Double 'why is this a decimal(2,1)?
    Public Property LastName As String
    Public Property FirstName As String

    Public Shared Function FromDataRow(ByVal data As IDataRecord) As Employee
         Dim result As New Employee()
         result.ID = CDbl(data("ID"))
         result.LastName = CStr(data("LastName"))
         result.FirstName = CStr(data("FirstName"))
         Return result
    End Function
End Class

Public Module DataLayer
    'Check www.connectionstring.com for more info on connection strings
    Private Property ConnectionString As String = "database connection string here"

    Private Iterator Function GetRecords(ByVal sql As String, ByVal addParams As Action(Of SqlParameterCollection)) As IEnumerable(Of IDataRecord)
        Using cn As New SqlConnection(ConnectionString), _
              cmd As New SqlCommand(sql, cn)

            addParams(cmd.Parameters)
            cn.Open()
            Using rdr As SqlDataReader = cmd.ExecuteReader()
                While rdr.Read)
                    Yield Return rdr
                End While
            End Using
        End Using
    End Function 

    Private Function GetRecords(Of T)(ByVal sql As String, ByVal addParams As Action(Of SqlParameterCollection), ByVal translate As Function(Of IDataRecord, T)) As IEnumerable(Of T)
       Return GetRecords(sql, addParams).Select(translate)
    End Function

    Public Function GetEmployeeData(ByVal EmployeeID As String) As Employee
        Dim sql As String = _
         "SELECT employee_id, name_last, name_first " & _ 
         "FROM employees " & _
         "WHERE employee_id= @ID"

        Return GetRecords(sql, _
            Sub(p) p.Add("@ID", SqlDbType.NVarChar, 10).Value = EmployeeID, _
            Employee.FromDataRow).First()
    End Function
End Class

Answer 2

To answer your second request, try to execute the following query:

Dim Query = "INSERT INTO Attendance (name_first, name_last, points) VALUES(var_first_name, var_last_name, var_points)"

Note that i did not insert the var_empid because if you have created your table correctly, this id should be an auto-generated primary key that increments itself automatically.

Answer 3

It's not easy to start because at first you see so many different names and technologies and they all seem to promise, more or less, the same thing. Especially if you want to build a database-connected application, and start doing basic stuff like CRUD operations (inserts, updates, deletes...), it's easy to get confused.

Start reading here about ADO.NET Architecture . You hopefully will understand something more about DataSet , Linq To SQL , Entity Framework , but probably not much. This is why I strongly suggest to take a few days and slowly watch the tutorial videos by Beth Massi, on VB.Net and Data.

On this page, How Do I Videos for Visual Basic , you will find a lot of useful information to start building simple but very effective applications and database. Be sure to watch Forms over Data Video Series , Visual Basic 2008 Forms over Data Videos (using DataSets ) and then Language Integrated Query (LINQ) Series (using LINQ To SQL where you'll understand why in your vb.net application your object variables have the same name as your database columns). FInally you can take a look at the Entity Framework tutorial (that you will find very similar to Linq To SQL).

After these basic tutorials you'll be able to choose your path and start programming. Once you grasp the basic concepts it's a lot easier to search and understand what you find on the internet.