【译文】如何从一个表中指定一个控件的值

时　间:2013-09-03 09:04:27
作　者:周芳   ID：24526  城市：上海
摘　要:DLookup 函数用于从指定记录集（一个域）获取特定字段的值。可以在 Visual Basic、宏、查询表达式、窗体或报表上的计算控件中使用 DLookup 函数。

正　文:

来自：微软  翻译：周芳

【译文】如何从一个表中指定一个控件的值

      您可以使用DLookup函数来显示字段值不在记录来源表或报告。例如,假设您有一个基于订单详细信息的表。表显示了OrderID、ProductID,UnitPrice、Quantity和Discount字段。 然而,UnitPrice字段是在另一个产品表中。当用户选择一个产品，你可以使用DLookup函数在相同的表计算控制显示UnitPrice。

      下面的示例把当前选定的ProductID组合框中产品的价格填入到UnitPrice文本框。

VBA代码
Private Sub ProductID_AfterUpdate() 
 
’在传递给DLookup函数前评估过滤。

 strFilter = "ProductID = " & Me!ProductID 
 
’查找产品的单价将它赋值给UnitPrice控件。

 Me!UnitPrice = DLookup("UnitPrice", "Products", strFilter)
 
End Sub

      这个DLookup函数有三个参数。第一个参数指定要查找的字段(UnitPrice);第二个指定表(产品);第三个指定找到的值(与ProductID一样的当前记录在订单子表的ProductID值)。

原文：How to: Assign a Control a Value From a Table

      You can use the DLookup function to display the value of a field that is not in the record source for your form or report. For example, suppose you have a form based on an order Details table. The form displays the orderID, ProductID, UnitPrice, Quantity, and Discount fields. However, the UnitPrice field is in another table: Products. You could use the DLookup function in a calculated control to display the UnitPrice on the same form when the user selects a product.

      The following example populates the UnitPrice text box with the price of the product currently selected in the ProductID combo box.

VBA
Private Sub ProductID_AfterUpdate()
 
 ' Evaluate filter before it is passed to DLookup function. 
 strFilter = "ProductID = " & Me!ProductID
 
 ' Look up product's unit price and assign it to the UnitPrice control. 
 Me!UnitPrice = DLookup("UnitPrice", "Products", strFilter)
 
End Sub

      The DLookup function has three arguments. The first specifies the field you are looking up (UnitPrice); the second specifies the table (Products); and the third specifies which value to find (the value for the record where the ProductID is the same as the ProductID on the current record in the orders subform).