Build a complete customer workspace

{
  "schemaVersion": 1,
  "projectId": "e3175003-dc5c-4f73-846b-c4dcfb5a87c1",
  "name": "CustomerDesk",
  "kind": "DesktopApp",
  "language": {
    "dialect": "McBasic1",
    "requireExplicit": true,
    "compare": "Binary",
    "defaultArrayBase": 0
  },
  "application": {
    "bundleIdentifier": "com.mcbasic.samples.customerdesk",
    "version": "0.1.0",
    "buildNumber": "1",
    "startupFormId": "form-customers",
    "shutdownMode": "OnStartupFormClosed"
  },
  "forms": [
    {
      "id": "form-customers",
      "typeName": "frmCustomers",
      "layout": "Forms/frmCustomers.form.json",
      "code": "Forms/frmCustomers.bas"
    },
    {
      "id": "form-customer",
      "typeName": "frmCustomer",
      "layout": "Forms/frmCustomer.form.json",
      "code": "Forms/frmCustomer.bas"
    }
  ],
  "modules": [],
  "classes": [],
  "tests": [],
  "references": [],
  "resources": [],
  "targets": [
    "osx-arm64"
  ],
  "capabilities": [],
  "migrations": [
    {
      "id": 1,
      "path": "Database/migrations/0001_initial.sql"
    }
  ]
}

Private Async Sub Form_Shown()
    Dim version As Long
    Dim loaded As Boolean

    mBusy = True
    cmdAdd.Enabled = False
    cmdOpen.Enabled = False
    cmdFilter.Enabled = False
    cmdRefresh.Enabled = False
    cmdExport.Enabled = False
    cmdReport.Enabled = False
    cmdCancelAdd.Enabled = False
    lblStatus.Caption = "Opening customer database..."
    Try
        Set mDb = Await Sqlite.OpenAsync(AppPaths.DataFile("customerdesk.db"))
        version = Await mDb.ApplyMigrationsAsync(App.Migrations)
        loaded = Await ReloadCustomers()
        cmdAdd.Enabled = True
        cmdOpen.Enabled = True
        cmdFilter.Enabled = True
        cmdRefresh.Enabled = True
        cmdExport.Enabled = True
        cmdReport.Enabled = True
    Catch failure As McException
        lblStatus.Caption = "Database error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdReport_Click()
    Dim command As DbCommand
    Dim rows As Recordset
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdReport.Enabled = False
    lblStatus.Caption = "Preparing customerdesk.pdf..."
    Try
        Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers ORDER BY name, id")
        Set rows = Await command.QueryAsync()
        Await Reports.ExportTablePdfAsync(rows, "CustomerDesk — Customers", AppPaths.DataFile("customerdesk.pdf"))
        lblStatus.Caption = CStr(rows.RowCount) & " customer(s) reported to customerdesk.pdf."
    Catch failure As McException
        lblStatus.Caption = "Report error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdReport.Enabled = True
    End Try
End Sub

Private Async Function ReloadCustomers() As Boolean
    Dim command As DbCommand
    Dim pattern As String

    pattern = "%" & Trim$(txtFilter.Text) & "%"
    Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers WHERE name LIKE @pattern ORDER BY name, id")
    command.AddParameter "@pattern", pattern
    Set mRows = Await command.QueryAsync()
    Set grdCustomers.DataSource = mRows.Bind()
    grdCustomers.SelectedIndex = -1
    lblStatus.Caption = CStr(mRows.RowCount) & " customer(s)"
    ReloadCustomers = True
End Function

Private Async Sub cmdFilter_Click()
    Dim loaded As Boolean
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    Try
        loaded = Await ReloadCustomers()
    Catch failure As McException
        lblStatus.Caption = "Filter error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdRefresh_Click()
    Dim loaded As Boolean
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    Try
        loaded = Await ReloadCustomers()
    Catch failure As McException
        lblStatus.Caption = "Refresh error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdAdd_Click()
    Dim command As DbCommand
    Dim affected As LongLong
    Dim loaded As Boolean
    Dim email As Variant
    Dim operationReturned As Boolean
    Dim handledError As Boolean

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    If Len(Trim$(txtName.Text)) = 0 Then
        lblStatus.Caption = "Name is required."
        txtName.SetFocus
        Exit Sub
    End If
    If Len(Trim$(txtEmail.Text)) = 0 Then
        email = Null
    Else
        email = Trim$(txtEmail.Text)
    End If
    mBusy = True
    mAddCancelRequested = False
    cmdAdd.Enabled = False
    Try
        Set command = mDb.CreateCommand("INSERT INTO customers(name, email) VALUES(@name, @email)")
        command.AddParameter "@name", Trim$(txtName.Text)
        command.AddParameter "@email", email
        Set mAddCommand = command
        cmdCancelAdd.Enabled = True
        affected = Await command.ExecuteAsync()
        operationReturned = True
        Set mAddCommand = Nothing
        cmdCancelAdd.Enabled = False
        If affected <> 1 Then
            lblStatus.Caption = "Insert affected an unexpected number of rows."
        Else
            txtName.Text = ""
            txtEmail.Text = ""
            loaded = Await ReloadCustomers()
        End If
    Catch failure As McException
        handledError = True
        lblStatus.Caption = "Save error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        Set mAddCommand = Nothing
        cmdCancelAdd.Enabled = False
        If mAddCancelRequested And Not operationReturned And Not handledError Then
            lblStatus.Caption = "Add stopped after cancellation request. Refresh to confirm the data."
        End If
        mBusy = False
        cmdAdd.Enabled = True
    End Try
End Sub

Private Sub cmdCancelAdd_Click()
    If Not mBusy Then Exit Sub
    If mAddCommand Is Nothing Then Exit Sub
    mAddCancelRequested = True
    cmdCancelAdd.Enabled = False
    lblStatus.Caption = "Cancelling Add..."
    mAddCommand.Cancel
End Sub

Private Sub cmdOpen_Click()
    Dim details As frmCustomer
    Dim row As Long

    If mBusy Then Exit Sub
    If mRows Is Nothing Then Exit Sub
    row = CInt(grdCustomers.SelectedIndex)
    If row < 0 Or row >= mRows.RowCount Then
        lblStatus.Caption = "Select a customer first."
        Exit Sub
    End If
    Set details = New frmCustomer
    details.CustomerId = CLng(mRows.Value(row, "id"))
    details.ExpectedVersion = CLng(mRows.Value(row, "version"))
    details.DisplayName = CStr(mRows.Value(row, "name"))
    If IsNull(mRows.Value(row, "email")) Then
        details.EmailAddress = ""
    Else
        details.EmailAddress = CStr(mRows.Value(row, "email"))
    End If
    details.Show
    lblStatus.Caption = "Editing customer " & CStr(details.CustomerId) & "; Refresh after closing details."
End Sub

Private Async Sub cmdExport_Click()
    Dim command As DbCommand
    Dim rows As Recordset
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdExport.Enabled = False
    Try
        Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers ORDER BY name, id")
        Set rows = Await command.QueryAsync()
        Await rows.ExportCsvAsync(AppPaths.DataFile("customerdesk.csv"))
        lblStatus.Caption = CStr(rows.RowCount) & " customer(s) exported."
    Catch failure As McException
        lblStatus.Caption = "Export error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdExport.Enabled = True
    End Try
End Sub

Private Sub cmdQuit_Click()
    If mBusy Then Exit Sub
    App.Quit
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    If mBusy Then
        Cancel = 1
        lblStatus.Caption = "Wait for the current operation."
    End If
End Sub

Private Sub Form_Unload()
    If Not mDb Is Nothing Then
        mDb.Dispose
        Set mDb = Nothing
    End If
End Sub

Option Explicit

Private mDb As Database
Private mRows As Recordset
Private mBusy As Boolean
Private mAddCommand As DbCommand
Private mAddCancelRequested As Boolean

Private Async Sub Form_Shown()
    Dim version As Long
    Dim loaded As Boolean

    mBusy = True
    cmdAdd.Enabled = False
    cmdOpen.Enabled = False
    cmdFilter.Enabled = False
    cmdRefresh.Enabled = False
    cmdExport.Enabled = False
    cmdReport.Enabled = False
    cmdCancelAdd.Enabled = False
    lblStatus.Caption = "Opening customer database..."
    Try
        Set mDb = Await Sqlite.OpenAsync(AppPaths.DataFile("customerdesk.db"))
        version = Await mDb.ApplyMigrationsAsync(App.Migrations)
        loaded = Await ReloadCustomers()
        cmdAdd.Enabled = True
        cmdOpen.Enabled = True
        cmdFilter.Enabled = True
        cmdRefresh.Enabled = True
        cmdExport.Enabled = True
        cmdReport.Enabled = True
    Catch failure As McException
        lblStatus.Caption = "Database error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdReport_Click()
    Dim command As DbCommand
    Dim rows As Recordset
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdReport.Enabled = False
    lblStatus.Caption = "Preparing customerdesk.pdf..."
    Try
        Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers ORDER BY name, id")
        Set rows = Await command.QueryAsync()
        Await Reports.ExportTablePdfAsync(rows, "CustomerDesk — Customers", AppPaths.DataFile("customerdesk.pdf"))
        lblStatus.Caption = CStr(rows.RowCount) & " customer(s) reported to customerdesk.pdf."
    Catch failure As McException
        lblStatus.Caption = "Report error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdReport.Enabled = True
    End Try
End Sub

Private Async Function ReloadCustomers() As Boolean
    Dim command As DbCommand
    Dim pattern As String

    pattern = "%" & Trim$(txtFilter.Text) & "%"
    Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers WHERE name LIKE @pattern ORDER BY name, id")
    command.AddParameter "@pattern", pattern
    Set mRows = Await command.QueryAsync()
    Set grdCustomers.DataSource = mRows.Bind()
    grdCustomers.SelectedIndex = -1
    lblStatus.Caption = CStr(mRows.RowCount) & " customer(s)"
    ReloadCustomers = True
End Function

Private Async Sub cmdFilter_Click()
    Dim loaded As Boolean
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    Try
        loaded = Await ReloadCustomers()
    Catch failure As McException
        lblStatus.Caption = "Filter error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdRefresh_Click()
    Dim loaded As Boolean
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    Try
        loaded = Await ReloadCustomers()
    Catch failure As McException
        lblStatus.Caption = "Refresh error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdAdd_Click()
    Dim command As DbCommand
    Dim affected As LongLong
    Dim loaded As Boolean
    Dim email As Variant
    Dim operationReturned As Boolean
    Dim handledError As Boolean

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    If Len(Trim$(txtName.Text)) = 0 Then
        lblStatus.Caption = "Name is required."
        txtName.SetFocus
        Exit Sub
    End If
    If Len(Trim$(txtEmail.Text)) = 0 Then
        email = Null
    Else
        email = Trim$(txtEmail.Text)
    End If
    mBusy = True
    mAddCancelRequested = False
    cmdAdd.Enabled = False
    Try
        Set command = mDb.CreateCommand("INSERT INTO customers(name, email) VALUES(@name, @email)")
        command.AddParameter "@name", Trim$(txtName.Text)
        command.AddParameter "@email", email
        Set mAddCommand = command
        cmdCancelAdd.Enabled = True
        affected = Await command.ExecuteAsync()
        operationReturned = True
        Set mAddCommand = Nothing
        cmdCancelAdd.Enabled = False
        If affected <> 1 Then
            lblStatus.Caption = "Insert affected an unexpected number of rows."
        Else
            txtName.Text = ""
            txtEmail.Text = ""
            loaded = Await ReloadCustomers()
        End If
    Catch failure As McException
        handledError = True
        lblStatus.Caption = "Save error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        Set mAddCommand = Nothing
        cmdCancelAdd.Enabled = False
        If mAddCancelRequested And Not operationReturned And Not handledError Then
            lblStatus.Caption = "Add stopped after cancellation request. Refresh to confirm the data."
        End If
        mBusy = False
        cmdAdd.Enabled = True
    End Try
End Sub

Private Sub cmdCancelAdd_Click()
    If Not mBusy Then Exit Sub
    If mAddCommand Is Nothing Then Exit Sub
    mAddCancelRequested = True
    cmdCancelAdd.Enabled = False
    lblStatus.Caption = "Cancelling Add..."
    mAddCommand.Cancel
End Sub

Private Sub cmdOpen_Click()
    Dim details As frmCustomer
    Dim row As Long

    If mBusy Then Exit Sub
    If mRows Is Nothing Then Exit Sub
    row = CInt(grdCustomers.SelectedIndex)
    If row < 0 Or row >= mRows.RowCount Then
        lblStatus.Caption = "Select a customer first."
        Exit Sub
    End If
    Set details = New frmCustomer
    details.CustomerId = CLng(mRows.Value(row, "id"))
    details.ExpectedVersion = CLng(mRows.Value(row, "version"))
    details.DisplayName = CStr(mRows.Value(row, "name"))
    If IsNull(mRows.Value(row, "email")) Then
        details.EmailAddress = ""
    Else
        details.EmailAddress = CStr(mRows.Value(row, "email"))
    End If
    details.Show
    lblStatus.Caption = "Editing customer " & CStr(details.CustomerId) & "; Refresh after closing details."
End Sub

Private Async Sub cmdExport_Click()
    Dim command As DbCommand
    Dim rows As Recordset
    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdExport.Enabled = False
    Try
        Set command = mDb.CreateCommand("SELECT id, name, email, version FROM customers ORDER BY name, id")
        Set rows = Await command.QueryAsync()
        Await rows.ExportCsvAsync(AppPaths.DataFile("customerdesk.csv"))
        lblStatus.Caption = CStr(rows.RowCount) & " customer(s) exported."
    Catch failure As McException
        lblStatus.Caption = "Export error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdExport.Enabled = True
    End Try
End Sub

Private Sub cmdQuit_Click()
    If mBusy Then Exit Sub
    App.Quit
End Sub


Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    If mBusy Then
        Cancel = 1
        lblStatus.Caption = "Wait for the current operation."
    End If
End Sub

Private Sub Form_Unload()
    If Not mDb Is Nothing Then
        mDb.Dispose
        Set mDb = Nothing
    End If
End Sub

Private Async Sub Form_Shown()
    mBusy = True
    cmdSave.Enabled = False
    cmdCancelSave.Enabled = False
    cmdReload.Enabled = False
    txtName.Text = DisplayName
    txtEmail.Text = EmailAddress
    lblStatus.Caption = "Opening customer " & CStr(CustomerId) & "..."
    Try
        Set mDb = Await Sqlite.OpenAsync(AppPaths.DataFile("customerdesk.db"))
        mRecordAvailable = True
        cmdSave.Enabled = True
        cmdReload.Enabled = True
        lblStatus.Caption = "Version " & CStr(ExpectedVersion)
    Catch failure As McException
        lblStatus.Caption = "Database error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdSave_Click()
    Dim command As DbCommand
    Dim current As DbCommand
    Dim rows As Recordset
    Dim affected As LongLong
    Dim email As Variant
    Dim updateReturned As Boolean
    Dim handledError As Boolean

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    If Not mRecordAvailable Then Exit Sub
    If Len(Trim$(txtName.Text)) = 0 Then
        lblStatus.Caption = "Name is required."
        txtName.SetFocus
        Exit Sub
    End If
    If Len(Trim$(txtEmail.Text)) = 0 Then
        email = Null
    Else
        email = Trim$(txtEmail.Text)
    End If
    mBusy = True
    mSaveCancelRequested = False
    cmdSave.Enabled = False
    cmdCancelSave.Enabled = False
    Try
        Set command = mDb.CreateCommand("UPDATE customers SET name=@name, email=@email, version=version+1 WHERE id=@id AND version=@expectedVersion")
        command.AddParameter "@name", Trim$(txtName.Text)
        command.AddParameter "@email", email
        command.AddParameter "@id", CustomerId
        command.AddParameter "@expectedVersion", ExpectedVersion
        Set mSaveCommand = command
        cmdCancelSave.Enabled = True
        affected = Await command.ExecuteAsync()
        updateReturned = True
        Set mSaveCommand = Nothing
        cmdCancelSave.Enabled = False
        If affected = 0 Then
            Set current = mDb.CreateCommand("SELECT version FROM customers WHERE id=@id")
            current.AddParameter "@id", CustomerId
            Set rows = Await current.QueryAsync()
            If rows.RowCount = 0 Then
                mRecordAvailable = False
                lblStatus.Caption = "Customer no longer exists. Close this detail."
            Else
                lblStatus.Caption = "Conflict: this customer changed. Discard & reload to see the current version."
            End If
        Else
            ExpectedVersion = ExpectedVersion + 1
            DisplayName = Trim$(txtName.Text)
            lblStatus.Caption = "Saved version " & CStr(ExpectedVersion) & ". Refresh the list."
        End If
    Catch failure As McException
        handledError = True
        lblStatus.Caption = "Save error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        Set mSaveCommand = Nothing
        cmdCancelSave.Enabled = False
        If mSaveCancelRequested And Not updateReturned And Not handledError Then
            lblStatus.Caption = "Save stopped after cancellation request. Discard & reload to confirm the current version."
        End If
        mBusy = False
        cmdSave.Enabled = mRecordAvailable
    End Try
End Sub

Private Sub cmdCancelSave_Click()
    If Not mBusy Then Exit Sub
    If mSaveCommand Is Nothing Then Exit Sub
    mSaveCancelRequested = True
    cmdCancelSave.Enabled = False
    lblStatus.Caption = "Cancelling Save..."
    mSaveCommand.Cancel
End Sub

Private Async Sub cmdReload_Click()
    Dim command As DbCommand
    Dim rows As Recordset

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdSave.Enabled = False
    cmdReload.Enabled = False
    Try
        Set command = mDb.CreateCommand("SELECT name, email, version FROM customers WHERE id=@id")
        command.AddParameter "@id", CustomerId
        Set rows = Await command.QueryAsync()
        If rows.RowCount = 0 Then
            mRecordAvailable = False
            lblStatus.Caption = "Customer no longer exists. Close this detail."
        Else
            mRecordAvailable = True
            DisplayName = CStr(rows.Value(0, "name"))
            If IsNull(rows.Value(0, "email")) Then
                EmailAddress = ""
            Else
                EmailAddress = CStr(rows.Value(0, "email"))
            End If
            ExpectedVersion = CLng(rows.Value(0, "version"))
            txtName.Text = DisplayName
            txtEmail.Text = EmailAddress
            lblStatus.Caption = "Loaded version " & CStr(ExpectedVersion) & ". Unsaved edits were discarded."
        End If
    Catch failure As McException
        lblStatus.Caption = "Reload error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdSave.Enabled = mRecordAvailable
        cmdReload.Enabled = True
    End Try
End Sub

Private Sub cmdClose_Click()
    If mBusy Then Exit Sub
    Unload Me
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    If mBusy Then
        Cancel = 1
        lblStatus.Caption = "Wait for the current operation."
    End If
End Sub

Private Sub Form_Unload()
    If Not mDb Is Nothing Then
        mDb.Dispose
        Set mDb = Nothing
    End If
End Sub

Option Explicit

Public CustomerId As Long
Public ExpectedVersion As Long
Public DisplayName As String
Public EmailAddress As String

Private mDb As Database
Private mBusy As Boolean
Private mRecordAvailable As Boolean
Private mSaveCommand As DbCommand
Private mSaveCancelRequested As Boolean

Private Async Sub Form_Shown()
    mBusy = True
    cmdSave.Enabled = False
    cmdCancelSave.Enabled = False
    cmdReload.Enabled = False
    txtName.Text = DisplayName
    txtEmail.Text = EmailAddress
    lblStatus.Caption = "Opening customer " & CStr(CustomerId) & "..."
    Try
        Set mDb = Await Sqlite.OpenAsync(AppPaths.DataFile("customerdesk.db"))
        mRecordAvailable = True
        cmdSave.Enabled = True
        cmdReload.Enabled = True
        lblStatus.Caption = "Version " & CStr(ExpectedVersion)
    Catch failure As McException
        lblStatus.Caption = "Database error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
    End Try
End Sub

Private Async Sub cmdSave_Click()
    Dim command As DbCommand
    Dim current As DbCommand
    Dim rows As Recordset
    Dim affected As LongLong
    Dim email As Variant
    Dim updateReturned As Boolean
    Dim handledError As Boolean

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    If Not mRecordAvailable Then Exit Sub
    If Len(Trim$(txtName.Text)) = 0 Then
        lblStatus.Caption = "Name is required."
        txtName.SetFocus
        Exit Sub
    End If
    If Len(Trim$(txtEmail.Text)) = 0 Then
        email = Null
    Else
        email = Trim$(txtEmail.Text)
    End If
    mBusy = True
    mSaveCancelRequested = False
    cmdSave.Enabled = False
    cmdCancelSave.Enabled = False
    Try
        Set command = mDb.CreateCommand("UPDATE customers SET name=@name, email=@email, version=version+1 WHERE id=@id AND version=@expectedVersion")
        command.AddParameter "@name", Trim$(txtName.Text)
        command.AddParameter "@email", email
        command.AddParameter "@id", CustomerId
        command.AddParameter "@expectedVersion", ExpectedVersion
        Set mSaveCommand = command
        cmdCancelSave.Enabled = True
        affected = Await command.ExecuteAsync()
        updateReturned = True
        Set mSaveCommand = Nothing
        cmdCancelSave.Enabled = False
        If affected = 0 Then
            Set current = mDb.CreateCommand("SELECT version FROM customers WHERE id=@id")
            current.AddParameter "@id", CustomerId
            Set rows = Await current.QueryAsync()
            If rows.RowCount = 0 Then
                mRecordAvailable = False
                lblStatus.Caption = "Customer no longer exists. Close this detail."
            Else
                lblStatus.Caption = "Conflict: this customer changed. Discard & reload to see the current version."
            End If
        Else
            ExpectedVersion = ExpectedVersion + 1
            DisplayName = Trim$(txtName.Text)
            lblStatus.Caption = "Saved version " & CStr(ExpectedVersion) & ". Refresh the list."
        End If
    Catch failure As McException
        handledError = True
        lblStatus.Caption = "Save error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        Set mSaveCommand = Nothing
        cmdCancelSave.Enabled = False
        If mSaveCancelRequested And Not updateReturned And Not handledError Then
            lblStatus.Caption = "Save stopped after cancellation request. Discard & reload to confirm the current version."
        End If
        mBusy = False
        cmdSave.Enabled = mRecordAvailable
    End Try
End Sub

Private Sub cmdCancelSave_Click()
    If Not mBusy Then Exit Sub
    If mSaveCommand Is Nothing Then Exit Sub
    mSaveCancelRequested = True
    cmdCancelSave.Enabled = False
    lblStatus.Caption = "Cancelling Save..."
    mSaveCommand.Cancel
End Sub

Private Async Sub cmdReload_Click()
    Dim command As DbCommand
    Dim rows As Recordset

    If mBusy Then Exit Sub
    If mDb Is Nothing Then Exit Sub
    mBusy = True
    cmdSave.Enabled = False
    cmdReload.Enabled = False
    Try
        Set command = mDb.CreateCommand("SELECT name, email, version FROM customers WHERE id=@id")
        command.AddParameter "@id", CustomerId
        Set rows = Await command.QueryAsync()
        If rows.RowCount = 0 Then
            mRecordAvailable = False
            lblStatus.Caption = "Customer no longer exists. Close this detail."
        Else
            mRecordAvailable = True
            DisplayName = CStr(rows.Value(0, "name"))
            If IsNull(rows.Value(0, "email")) Then
                EmailAddress = ""
            Else
                EmailAddress = CStr(rows.Value(0, "email"))
            End If
            ExpectedVersion = CLng(rows.Value(0, "version"))
            txtName.Text = DisplayName
            txtEmail.Text = EmailAddress
            lblStatus.Caption = "Loaded version " & CStr(ExpectedVersion) & ". Unsaved edits were discarded."
        End If
    Catch failure As McException
        lblStatus.Caption = "Reload error " & CStr(failure.Number) & ": " & failure.Message
    Finally
        mBusy = False
        cmdSave.Enabled = mRecordAvailable
        cmdReload.Enabled = True
    End Try
End Sub

Private Sub cmdClose_Click()
    If mBusy Then Exit Sub
    Unload Me
End Sub

Private Sub Form_QueryUnload(ByRef Cancel As Integer, ByVal UnloadMode As Integer)
    If mBusy Then
        Cancel = 1
        lblStatus.Caption = "Wait for the current operation."
    End If
End Sub

Private Sub Form_Unload()
    If Not mDb Is Nothing Then
        mDb.Dispose
        Set mDb = Nothing
    End If
End Sub

CREATE TABLE customers (
    id INTEGER PRIMARY KEY,
    name TEXT NOT NULL,
    email TEXT NULL,
    version INTEGER NOT NULL DEFAULT 1
);