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Required: Making the User Enter a Value The Required property is very important: It determines whether you require that a value be entered into a field. This property is useful for foreign key fields, when you want to make sure data is entered into the field. It’s also useful for any field containing information that’s needed for business reasons (company name, for example).

NOTE: A foreign key field is a field that is looked up in another table. For example, in the case of a Customers table and an Orders table, both might contain a CustomerID field. In the Customers table, the CustomerID is the primary key field. In the Orders table, the CustomerID is the foreign key field because its value is looked up in the Customers table.

Set the Required property of the CompanyName and PhoneNumber fields to Yes. Switch to Datasheet view and try to add a new record, leaving the CompanyName and PhoneNumber fields blank. Make sure you enter a value for at least one of the other fields in the record. When you try to move off the record, the error message shown in Figure 2.13 appears.

FIGURE 2.13 A message appears when you leave blank a field that has the Required property set to Yes.

Allow Zero Length: Accommodating Situations with Nonexistent Data The Allow Zero Length property is similar to the Required property. Use it to determine whether you allow the user to enter a zero-length string (“”). A zero-length string isn’t the same as a Null (which represents the absence of an entry); a zero-length string indicates that the data doesn’t exist for that particular field. For example, a foreign employee might not have a Social Security number. When you enter a zero-length string, the data entry person can indicate that the Social Security number doesn’t exist.

Add a new field called ContactName and set its Required property to Yes. Try to add a new record and enter two quotation marks (“”) in the ContactName field. You should not get an error message because, in Access 2007, the Allow Zero Length property defaults to Yes. Your zero-length string will appear blank when you move off the field. Return to the Design view of the table. Change the setting for the Allow Zero Length property to No. Go back to Datasheet view and once again enter two quotation marks in the ContactName field. This time you should not be successful. You should get the error message shown in Figure 2.14.

FIGURE 2.14 The result of entering “” when the Allow Zero Length property is set to No.

CAUTION: In previous versions of Access, the default setting for the Allow Zero Length property was No. Under Access 2002, Access 2003, and Access 2007, Microsoft has changed this default setting to Yes. Pay close attention to this default behavior, especially if you’re accustomed to working with prior releases of the product.

This material orginally appeared in Alison Balter's book Mastering Microsoft Office Access 2007 Development. Reprinted here by author's permission.

When you need a Microsoft Access programmer for your Sacramento CA business, phone call MS Access Solutions at (323) 285-0939. We have over 25 years experience in Microsoft Access programmer solutions. We create Access database applications for all sectors, consisting of hospitals, government companies, the U.S. military, universities, agriculture, workers services, and insurance provider. We can take care of the most advanced as well as complicated Access and also SQL Server database programming for your business as well as smaller projects, like fixing damaged Access database forms, MS Access reports, Access macros, and VBA code.

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