Emmeline's Land 艾玛琳园地: December 2012

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为了建立一个健壮的J2EE应用，将所有对数据源的访问操作抽象封装在一个公共API中（建立一个接口）。
用户需要通过这接口，来进行和数据源的所有事务、交互。

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DAO (Data Access Objects）（数据访问对象）是一种应用程序编程接口（API）。
DAO是程序员访问数据库【Access数据库、其他的结构化查询语言（SQL）数据库】的第一个面向对象的数据库接口。
它夹在业务逻辑与数据库资源中间。
它显露 Microsoft Jet数据库“引擎”（由 Microsoft Access 所使用），并允许开发者通过 ODBC 象直接连接到其他数据库一样，直接连接到数据库表。
DAO 最适用于单系统应用程序或小范围本地分布使用。
DAO是Data Access Object数据访问接口，数据访问：顾名思义就是与数据库打交道。夹在业务逻辑与数据库资源中间。

开发人员使用数据访问对象（DAO）设计模式把底层的数据访问逻辑和高层的商务逻辑分开。

如何设计和实现数据访问对象？

哪些是事务性对象？
事务划分（transaction demarcation)包括：-

编程性事务（programmatic）: 程序员担负编写事务逻辑代码的责任。
声明性事务（declarative） : 程序员使用EJB的部署描述符声明事务属性。

DAO模式是标准的J2EE设计模式之一.开发人员使用这个模式把底层的数据访问操作和上层的商务逻辑分开。

一个典型的DAO实现有下列几个组件：

一个DAO工厂类 (DaoFactory @ ConnectionFactory Class)
一个DAO接口 (Dao Interface)
一个实现DAO接口的具体类 (Implementation Class)
数据传递对象（值对象）

需知相关信息：

数据访问对象DAO的结构
数据访问对象DAO的功能
实战应用——使用数据访问对象DAO

。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。 Example (Visual Basic): How to use the DAO library to create, delete, modify and list the objects in Access.

[from: http://allenbrowne.com/func-dao.html]

Option Compare Database
Option Explicit

'Constants for examining how a field is indexed.
Private Const intcIndexNone As Integer = 0
Private Const intcIndexGeneral As Integer = 1
Private Const intcIndexUnique As Integer = 3
Private Const intcIndexPrimary As Integer = 7

Function CreateTableDAO()
    'Purpose:   Create two tables using DAO.
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    
    'Initialize the Contractor table.
    Set db = CurrentDb()
    Set tdf = db.CreateTableDef("tblDaoContractor")
    
    'Specify the fields.
    With tdf
        'AutoNumber: Long with the attribute set.
        Set fld = .CreateField("ContractorID", dbLong)
        fld.Attributes = dbAutoIncrField + dbFixedField
        .Fields.Append fld
        
        'Text field: maximum 30 characters, and required.
        Set fld = .CreateField("Surname", dbText, 30)
        fld.Required = True
        .Fields.Append fld
        
        'Text field: maximum 20 characters.
        .Fields.Append .CreateField("FirstName", dbText, 20)
        
        'Yes/No field.
        .Fields.Append .CreateField("Inactive", dbBoolean)
        
        'Currency field.
        .Fields.Append .CreateField("HourlyFee", dbCurrency)
        
        'Number field.
        .Fields.Append .CreateField("PenaltyRate", dbDouble)
        
        'Date/Time field with validation rule.
        Set fld = .CreateField("BirthDate", dbDate)
        fld.ValidationRule = "Is Null Or <=Date()"
        fld.ValidationText = "Birth date cannot be future."
        .Fields.Append fld
        
        'Memo field.
        .Fields.Append .CreateField("Notes", dbMemo)
        
        'Hyperlink field: memo with the attribute set.
        Set fld = .CreateField("Web", dbMemo)
        fld.Attributes = dbHyperlinkField + dbVariableField
        .Fields.Append fld
    End With
    
    'Save the Contractor table.
    db.TableDefs.Append tdf
    Set fld = Nothing
    Set tdf = Nothing
    Debug.Print "tblDaoContractor created."
    
    'Initialize the Booking table
    Set tdf = db.CreateTableDef("tblDaoBooking")
    With tdf
        'Autonumber
        Set fld = .CreateField("BookingID", dbLong)
        fld.Attributes = dbAutoIncrField + dbFixedField
        .Fields.Append fld
        
        'BookingDate
        .Fields.Append .CreateField("BookingDate", dbDate)
        
        'ContractorID
        .Fields.Append .CreateField("ContractorID", dbLong)
        
        'BookingFee
        .Fields.Append .CreateField("BookingFee", dbCurrency)
        
        'BookingNote: Required.
        Set fld = .CreateField("BookingNote", dbText, 255)
        fld.Required = True
        .Fields.Append fld
    End With
    
    'Save the Booking table.
    db.TableDefs.Append tdf
    Set fld = Nothing
    Set tdf = Nothing
    Debug.Print "tblDaoBooking created."
    
    'Clean up
    Application.RefreshDatabaseWindow   'Show the changes
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Function

Function ModifyTableDAO()
    'Purpose:   How to add and delete fields to existing tables.
    'Note:      Requires the table created by CreateTableDAO() above.
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    
    'Initialize
    Set db = CurrentDb()

    Set tdf = db.TableDefs("tblDaoContractor")
    
    'Add a field to the table.
    tdf.Fields.Append tdf.CreateField("TestField", dbText, 80)
    Debug.Print "Field added."
    
    'Delete a field from the table.
    tdf.Fields.Delete "TestField"
    Debug.Print "Field deleted."
    
    'Clean up
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Function

Function DeleteTableDAO()
    DBEngine(0)(0).TableDefs.Delete "DaoTest"
End Function

Function MakeGuidTable()
    'Purpose:   How to create a table with a GUID field.
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    Dim prp As DAO.Property

    Set db = CurrentDb()
    Set tdf = db.CreateTableDef("Table8")
    With tdf
        Set fld = .CreateField("ID", dbGUID)
        fld.Attributes = dbFixedField
        fld.DefaultValue = "GenGUID()"
        .Fields.Append fld
    End With
    db.TableDefs.Append tdf
End Function

Function CreateIndexesDAO()
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim ind As DAO.Index
    
    'Initialize
    Set db = CurrentDb()
    Set tdf = db.TableDefs("tblDaoContractor")
    
    '1. Primary key index.
    Set ind = tdf.CreateIndex("PrimaryKey")
    With ind
        .Fields.Append .CreateField("ContractorID")
        .Unique = False
        .Primary = True
    End With
    tdf.Indexes.Append ind
    
    '2. Single-field index.
    Set ind = tdf.CreateIndex("Inactive")
    ind.Fields.Append ind.CreateField("Inactive")
    tdf.Indexes.Append ind
    
    '3. Multi-field index.
    Set ind = tdf.CreateIndex("FullName")
    With ind
        .Fields.Append .CreateField("Surname")
        .Fields.Append .CreateField("FirstName")
    End With
    tdf.Indexes.Append ind
    
    'Refresh the display of this collection.
    tdf.Indexes.Refresh
    
    'Clean up
    Set ind = Nothing
    Set tdf = Nothing
    Set db = Nothing
    Debug.Print "tblDaoContractor indexes created."
End Function

Function DeleteIndexDAO()
    DBEngine(0)(0).TableDefs("tblDaoContractor").Indexes.Delete "Inactive"
End Function

Function CreateRelationDAO()
    Dim db As DAO.Database
    Dim rel As DAO.Relation
    Dim fld As DAO.Field
    
    'Initialize
    Set db = CurrentDb()
    
    'Create a new relation.
    Set rel = db.CreateRelation("tblDaoContractortblDaoBooking")
    
    'Define its properties.
    With rel
        'Specify the primary table.
        .Table = "tblDaoContractor"
        'Specify the related table.
        .ForeignTable = "tblDaoBooking"
        'Specify attributes for cascading updates and deletes.
        .Attributes = dbRelationUpdateCascade + dbRelationDeleteCascade
        
        'Add the fields to the relation.
        'Field name in primary table.
        Set fld = .CreateField("ContractorID")
        'Field name in related table.
        fld.ForeignName = "ContractorID"
        'Append the field.
        .Fields.Append fld
        
        'Repeat for other fields if a multi-field relation.
    End With
    
    'Save the newly defined relation to the Relations collection.
    db.Relations.Append rel
    
    'Clean up
    Set fld = Nothing
    Set rel = Nothing
    Set db = Nothing
    Debug.Print "Relation created."
End Function

Function DeleteRelationDAO()
    DBEngine(0)(0).Relations.Delete "tblDaoContractortblDaoBooking"
End Function

Function DeleteQueryDAO()
    DBEngine(0)(0).QueryDefs.Delete "qryDaoBooking"
End Function

Function SetPropertyDAO(obj As Object, strPropertyName As String, intType As Integer, _
    varValue As Variant, Optional strErrMsg As String) As Boolean
On Error GoTo ErrHandler
    'Purpose:   Set a property for an object, creating if necessary.
    'Arguments: obj = the object whose property should be set.
    '           strPropertyName = the name of the property to set.
    '           intType = the type of property (needed for creating)
    '           varValue = the value to set this property to.
    '           strErrMsg = string to append any error message to.
    
    If HasProperty(obj, strPropertyName) Then
        obj.Properties(strPropertyName) = varValue
    Else
        obj.Properties.Append obj.CreateProperty(strPropertyName, intType, varValue)
    End If
    SetPropertyDAO = True

ExitHandler:
    Exit Function

ErrHandler:
    strErrMsg = strErrMsg & obj.Name & "." & strPropertyName & " not set to " & varValue & _
        ". Error " & Err.Number & " - " & Err.Description & vbCrLf
    Resume ExitHandler
End Function

Public Function HasProperty(obj As Object, strPropName As String) As Boolean
    'Purpose:   Return true if the object has the property.
    Dim varDummy As Variant
    
    On Error Resume Next
    varDummy = obj.Properties(strPropName)
    HasProperty = (Err.Number = 0)
End Function

Function StandardProperties(strTableName As String)
    'Purpose:   Properties you always want set by default:
    '           TableDef:        Subdatasheets off.
    '           Numeric fields:  Remove Default Value.
    '           Currency fields: Format as currency.
    '           Yes/No fields:   Display as check box. Default to No.
    '           Text/memo/hyperlink: AllowZeroLength off,
    '                                UnicodeCompression on.
    '           All fields:      Add a caption if mixed case.
    'Argument:  Name of the table.
    'Note:      Requires: SetPropertyDAO()
    Dim db As DAO.Database      'Current database.
    Dim tdf As DAO.TableDef     'Table nominated in argument.
    Dim fld As DAO.Field        'Each field.
    Dim strCaption As String    'Field caption.
    Dim strErrMsg As String     'Responses and error messages.
    
    'Initalize.
    Set db = CurrentDb()
    Set tdf = db.TableDefs(strTableName)
    
    'Set the table's SubdatasheetName.
    Call SetPropertyDAO(tdf, "SubdatasheetName", dbText, "[None]", _
        strErrMsg)
    
    For Each fld In tdf.Fields
        'Handle the defaults for the different field types.
        Select Case fld.Type
        Case dbText, dbMemo 'Includes hyperlinks.
            fld.AllowZeroLength = False
            Call SetPropertyDAO(fld, "UnicodeCompression", dbBoolean, _
                True, strErrMsg)
        Case dbCurrency
            fld.DefaultValue = 0
            Call SetPropertyDAO(fld, "Format", dbText, "Currency", _
                strErrMsg)
        Case dbLong, dbInteger, dbByte, dbDouble, dbSingle, dbDecimal
            fld.DefaultValue = vbNullString
        Case dbBoolean
            Call SetPropertyDAO(fld, "DisplayControl", dbInteger, _
                CInt(acCheckBox))
        End Select
        
        'Set a caption if needed.
        strCaption = ConvertMixedCase(fld.Name)
        If strCaption <> fld.Name Then
            Call SetPropertyDAO(fld, "Caption", dbText, strCaption)
        End If
        
        'Set the field's Description.
        Call SetFieldDescription(tdf, fld, , strErrMsg)
    Next
    
    'Clean up.
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
    If Len(strErrMsg) > 0 Then
        Debug.Print strErrMsg
    Else
        Debug.Print "Properties set for table " & strTableName
    End If
End Function

Function ConvertMixedCase(ByVal strIn As String) As String
    'Purpose:   Convert mixed case name into a name with spaces.
    'Argument:  String to convert.
    'Return:    String converted by these rules:
    '           1. One space before an upper case letter.
    '           2. Replace underscores with spaces.
    '           3. No spaces between continuing upper case.
    'Example:   "FirstName" or "First_Name" => "First Name".
    Dim lngStart As Long        'Loop through string.
    Dim strOut As String        'Output string.
    Dim boolWasSpace As Boolean 'Last char. was a space.
    Dim boolWasUpper As Boolean 'Last char. was upper case.
    
    strIn = Trim$(strIn)        'Remove leading/trailing spaces.
    boolWasUpper = True         'Initialize for no first space.
    
    For lngStart = 1& To Len(strIn)
        Select Case Asc(Mid(strIn, lngStart, 1&))
        Case vbKeyA To vbKeyZ   'Upper case: insert a space.
            If boolWasSpace Or boolWasUpper Then
                strOut = strOut & Mid(strIn, lngStart, 1&)
            Else
                strOut = strOut & " " & Mid(strIn, lngStart, 1&)
            End If
            boolWasSpace = False
            boolWasUpper = True
            
        Case 95                 'Underscore: replace with space.
            If Not boolWasSpace Then
                strOut = strOut & " "
            End If
            boolWasSpace = True
            boolWasUpper = False
            
        Case vbKeySpace         'Space: output and set flag.
            If Not boolWasSpace Then
                strOut = strOut & " "
            End If
            boolWasSpace = True
            boolWasUpper = False
            
        Case Else               'Any other char: output.
            strOut = strOut & Mid(strIn, lngStart, 1&)
            boolWasSpace = False
            boolWasUpper = False
        End Select
    Next
    
    ConvertMixedCase = strOut
End Function

Function SetFieldDescription(tdf As DAO.TableDef, fld As DAO.Field, _
Optional ByVal strDescrip As String, Optional strErrMsg As String) _
As Boolean
    'Purpose:   Assign a Description to a field.
    'Arguments: tdf = the TableDef the field belongs to.
    '           fld = the field to document.
    '           strDescrip = The description text you want.
    '                        If blank, uses Caption or Name of field.
    '           strErrMsg  = string to append any error messages to.
    'Notes:     Description includes field size, validation,
    '               whether required or unique.
    
    If (fld.Attributes And dbAutoIncrField) > 0& Then
        strDescrip = strDescrip & " Automatically generated " & _
            "unique identifier for this record."
    Else
        'If no description supplied, use the field's Caption or Name.
        If Len(strDescrip) = 0& Then
            If HasProperty(fld, "Caption") Then
                If Len(fld.Properties("Caption")) > 0& Then
                    strDescrip = fld.Properties("Caption") & "."
                End If
            End If
            If Len(strDescrip) = 0& Then
                strDescrip = fld.Name & "."
            End If
        End If
        
        'Size of the field.
        'Ignore Date, Memo, Yes/No, Currency, Decimal, GUID,
        '   Hyperlink, OLE Object.
        Select Case fld.Type
        Case dbByte, dbInteger, dbLong
            strDescrip = strDescrip & " Whole number."
        Case dbSingle, dbDouble
            strDescrip = strDescrip & " Fractional number."
        Case dbText
            strDescrip = strDescrip & " " & fld.Size & "-char max."
        End Select
        
        'Required and/or Unique?
        'Check for single-field index, and Required property.
        Select Case IndexOnField(tdf, fld)
        Case intcIndexPrimary
            strDescrip = strDescrip & " Required. Unique."
        Case intcIndexUnique
            If fld.Required Then
                strDescrip = strDescrip & " Required. Unique."
            Else
                strDescrip = strDescrip & " Unique."
            End If
        Case Else
            If fld.Required Then
                strDescrip = strDescrip & " Required."
            End If
        End Select
        
        'Validation?
        If Len(fld.ValidationRule) > 0& Then
            If Len(fld.ValidationText) > 0& Then
                strDescrip = strDescrip & " " & fld.ValidationText
            Else
                strDescrip = strDescrip & " " & fld.ValidationRule
            End If
        End If
    End If
    
    If Len(strDescrip) > 0& Then
        strDescrip = Trim$(Left$(strDescrip, 255&))
        SetFieldDescription = SetPropertyDAO(fld, "Description", _
            dbText, strDescrip, strErrMsg)
    End If
End Function

Private Function IndexOnField(tdf As DAO.TableDef, fld As DAO.Field) _
As Integer
    'Purpose:   Indicate if there is a single-field index _
    '               on this field in this table.
    'Return:    The constant indicating the strongest type.
    Dim ind As DAO.Index
    Dim intReturn As Integer
    
    intReturn = intcIndexNone
    
    For Each ind In tdf.Indexes
        If ind.Fields.Count = 1 Then
            If ind.Fields(0).Name = fld.Name Then
                If ind.Primary Then
                    intReturn = (intReturn Or intcIndexPrimary)
                ElseIf ind.Unique Then
                    intReturn = (intReturn Or intcIndexUnique)
                Else
                    intReturn = (intReturn Or intcIndexGeneral)
                End If
            End If
        End If
    Next
    
    'Clean up
    Set ind = Nothing
    IndexOnField = intReturn
End Function

Function CreateQueryDAO()
    'Purpose:   How to create a query
    'Note:      Requires a table named MyTable.
    Dim db As DAO.Database
    Dim qdf As DAO.QueryDef
    
    Set db = CurrentDb()
    
    'The next line creates and automatically appends the QueryDef.
    Set qdf = db.CreateQueryDef("qryMyTable")
    
    'Set the SQL property to a string representing a SQL statement.
    qdf.SQL = "SELECT MyTable.* FROM MyTable;"
    
    'Do not append: QueryDef is automatically appended!

    Set qdf = Nothing
    Set db = Nothing
    Debug.Print "qryMyTable created."
End Function

Function CreateDatabaseDAO()
    'Purpose:   How to create a new database and set key properties.
    Dim dbNew As DAO.Database
    Dim prp As DAO.Property
    Dim strFile As String
    
    'Create the new database.
    strFile = "C:\SampleDAO.mdb"
    Set dbNew = DBEngine(0).CreateDatabase(strFile, dbLangGeneral)
    
    'Create example properties in new database.
    With dbNew
        Set prp = .CreateProperty("Perform Name AutoCorrect", dbLong, 0)
        .Properties.Append prp
        Set prp = .CreateProperty("Track Name AutoCorrect Info", _
            dbLong, 0)
        .Properties.Append prp
    End With
    
    'Clean up.
    dbNew.Close
    Set prp = Nothing
    Set dbNew = Nothing
    Debug.Print "Created " & strFile
End Function

Function ShowDatabaseProps()
    'Purpose:   List the properies of the current database.
    Dim db As DAO.Database
    Dim prp As DAO.Property
    
    Set db = CurrentDb()
    For Each prp In db.Properties
        Debug.Print prp.Name
    Next
    
    Set db = Nothing
End Function

Function ShowFields(strTable As String)
    'Purpose:   How to read the fields of a table.
    'Usage:     Call ShowFields("Table1")
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    
    Set db = CurrentDb()
    Set tdf = db.TableDefs(strTable)
    For Each fld In tdf.Fields
        Debug.Print fld.Name, FieldTypeName(fld)
    Next
    
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Function

Function ShowFieldsRS(strTable)
    'Purpose:   How to read the field names and types from a table or query.
    'Usage:     Call ShowFieldsRS("Table1")
    Dim rs As DAO.Recordset
    Dim fld As DAO.Field
    Dim strSql As String
    
    strSql = "SELECT " & strTable & ".* FROM " & strTable & " WHERE (False);"
    Set rs = DBEngine(0)(0).OpenRecordset(strSql)
    For Each fld In rs.Fields
        Debug.Print fld.Name, FieldTypeName(fld), "from " & fld.SourceTable & "." & fld.SourceField
    Next
    rs.Close
    Set rs = Nothing
End Function

Public Function FieldTypeName(fld As DAO.Field)
    'Purpose: Converts the numeric results of DAO fieldtype to text.
    'Note:    fld.Type is Integer, but the constants are Long.
    Dim strReturn As String         'Name to return
    
    Select Case CLng(fld.Type)
        Case dbBoolean: strReturn = "Yes/No"            ' 1
        Case dbByte: strReturn = "Byte"                 ' 2
        Case dbInteger: strReturn = "Integer"           ' 3
        Case dbLong                                     ' 4
            If (fld.Attributes And dbAutoIncrField) = 0& Then
                strReturn = "Long Integer"
            Else
                strReturn = "AutoNumber"
            End If
        Case dbCurrency: strReturn = "Currency"         ' 5
        Case dbSingle: strReturn = "Single"             ' 6
        Case dbDouble: strReturn = "Double"             ' 7
        Case dbDate: strReturn = "Date/Time"            ' 8
        Case dbBinary: strReturn = "Binary"             ' 9 (no interface)
        Case dbText                                     '10
            If (fld.Attributes And dbFixedField) = 0& Then
                strReturn = "Text"
            Else
                strReturn = "Text (fixed width)"
            End If
        Case dbLongBinary: strReturn = "OLE Object"     '11
        Case dbMemo                                     '12
            If (fld.Attributes And dbHyperlinkField) = 0& Then
                strReturn = "Memo"
            Else
                strReturn = "Hyperlink"
            End If
        Case dbGUID: strReturn = "GUID"                 '15
        
        'Attached tables only: cannot create these in JET.
        Case dbBigInt: strReturn = "Big Integer"        '16
        Case dbVarBinary: strReturn = "VarBinary"       '17
        Case dbChar: strReturn = "Char"                 '18
        Case dbNumeric: strReturn = "Numeric"           '19
        Case dbDecimal: strReturn = "Decimal"           '20
        Case dbFloat: strReturn = "Float"               '21
        Case dbTime: strReturn = "Time"                 '22
        Case dbTimeStamp: strReturn = "Time Stamp"      '23
        
        'Constants for complex types don't work prior to Access 2007.
        Case 101&: strReturn = "Attachment"         'dbAttachment
        Case 102&: strReturn = "Complex Byte"       'dbComplexByte
        Case 103&: strReturn = "Complex Integer"    'dbComplexInteger
        Case 104&: strReturn = "Complex Long"       'dbComplexLong
        Case 105&: strReturn = "Complex Single"     'dbComplexSingle
        Case 106&: strReturn = "Complex Double"     'dbComplexDouble
        Case 107&: strReturn = "Complex GUID"       'dbComplexGUID
        Case 108&: strReturn = "Complex Decimal"    'dbComplexDecimal
        Case 109&: strReturn = "Complex Text"       'dbComplexText
        Case Else: strReturn = "Field type " & fld.Type & " unknown"
    End Select
    
    FieldTypeName = strReturn
End Function

Function DAORecordsetExample()
    'Purpose:   How to open a recordset and loop through the records.
    'Note:      Requires a table named MyTable, with a field named MyField.
    Dim rs As DAO.Recordset
    Dim strSql As String
    
    strSql = "SELECT MyField FROM MyTable;"
    Set rs = DBEngine(0)(0).OpenRecordset(strSql)
    
    Do While Not rs.EOF
        Debug.Print rs!MyField
        rs.MoveNext
    Loop
    
    rs.Close
    Set rs = Nothing
End Function

Function ShowFormProperties(strFormName As String)
On Error GoTo Err_Handler
    'Purpose:   Loop through the controls on a form, showing names and properties.
    'Usage:     Call ShowFormProperties("Form1")
    Dim frm As Form
    Dim ctl As Control
    Dim prp As Property
    Dim strOut As String
    
    DoCmd.OpenForm strFormName, acDesign, WindowMode:=acHidden
    Set frm = Forms(strFormName)
    
    For Each ctl In frm
        For Each prp In ctl.Properties
            strOut = strFormName & "." & ctl.Name & "." & prp.Name & ": "
            strOut = strOut & prp.Type & vbTab
            strOut = strOut & prp.Value
            Debug.Print strOut
        Next
        If ctl.ControlType = acTextBox Then Stop
    Next
    
    Set frm = Nothing
    DoCmd.Close acForm, strFormName, acSaveNo

Exit_Handler:
    Exit Function

Err_Handler:
    Select Case Err.Number
    Case 2186:
        strOut = strOut & Err.Description
        Resume Next
    Case Else
        MsgBox "Error " & Err.Number & ": " & Err.Description, vbExclamation, "ShowFormProperties()"
        Resume Exit_Handler
    End Select
End Function

Public Function ExecuteInTransaction(strSql As String, Optional strConfirmMessage As String) As Long
On Error GoTo Err_Handler
    'Purpose:   Execute the SQL statement on the current database in a transaction.
    'Return:    RecordsAffected if zero or above.
    'Arguments: strSql = the SQL statement to be executed.
    '           strConfirmMessage = the message to show the user for confirmation. Number will be added to front.
    '           No confirmation if ZLS.
    '           -1 on error.
    '           -2 on user-cancel.
    Dim ws As DAO.Workspace
    Dim db As DAO.Database
    Dim bInTrans As Boolean
    Dim bCancel As Boolean
    Dim strMsg As String
    Dim lngReturn As Long
    Const lngcUserCancel = -2&
    
    Set ws = DBEngine(0)
    ws.BeginTrans
    bInTrans = True
    Set db = ws(0)
    db.Execute strSql, dbFailOnError
    lngReturn = db.RecordsAffected
    If strConfirmMessage <> vbNullString Then
        If MsgBox(lngReturn & " " & Trim$(strConfirmMessage), vbOKCancel + vbQuestion, "Confirm") <> vbOK Then
            bCancel = True
            lngReturn = lngcUserCancel
        End If
    End If
    
    'Commmit or rollback.
    If bCancel Then
        ws.Rollback
    Else
        ws.CommitTrans
    End If
    bInTrans = False

Exit_Handler:
    ExecuteInTransaction = lngReturn
    On Error Resume Next
    Set db = Nothing
    If bInTrans Then
        ws.Rollback
    End If
    Set ws = Nothing
    Exit Function

Err_Handler:
    MsgBox "Error " & Err.Number & ": " & Err.Description, vbExclamation, "ExecuteInTransaction()"
    lngReturn = -1
    Resume Exit_Handler
End Function

Function GetAutoNumDAO(strTable) As String
    'Purpose:   Get the name of the AutoNumber field, using DAO.
    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field
    
    Set db = CurrentDb()
    Set tdf = db.TableDefs(strTable)
    
    For Each fld In tdf.Fields
        If (fld.Attributes And dbAutoIncrField) <> 0 Then
            GetAutoNumDAO = fld.Name
            Exit For
        End If
    Next
    
    Set fld = Nothing
    Set tdf = Nothing
    Set db = Nothing
End Function

Emmeline's Land 艾玛琳园地

Thursday, 20 December 2012

Letter of Authorization

Wednesday, 12 December 2012

Programming Language

What is DAO?

来源：

如何设计和实现数据访问对象？

DAO模式是标准的J2EE设计模式之一.开发人员使用这个模式把底层的数据访问操作和上层的商务逻辑分开。

一个典型的DAO实现有下列几个组件：

。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。。 Example (Visual Basic): How to use the DAO library to create, delete, modify and list the objects in Access.