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Chapter 11 Homework Solutions:

Chapter 11-Accessing Database Files

ANSWERS TO REVIEW QUESTIONS

1. Assume you have a database containing the names and phone numbers of yourfriends. Describe how the termsfile, table, row, column, record, field, andkey apply to

your database.

The names and phone numbers for your friends are stored in a table with rows (horizontal)

and columns (vertical). An Access database file can contain multiple related tables. Each

row in the table contains the information for one friend. Each row is called a record. The

information about the friends is separated into individual elements, called fields. In this

case, there are two elements in the friends database, name and phone number. Each of

these elements is called a field and is represented by the columns of the table. The key is

the unique field that is used to identify the record. The table is usually arranged by the key

field. In the friends database the key field would be the name field.

2. Explain the difference between a data control and a data-bound control.A Data control is created using the DataControl tool from the toolbox. A Data control

generally links one form with one table from a database. Using a data control is a two-step

process. First, you place a data control on a form and set the properties to link it to a

database file and table. Data-bound controls, such as text boxes and labels, display the

actual data from the field in the attached database table. Data-bound controls will

automatically display the contents of the bound field when the project runs.

3. Which controls can be data bound?The controls which can become data-bound (data aware controls) are labels, text boxes,

check boxes, list boxes, combo boxes, images, picture boxes, data-bound list boxes, data-

bound combo boxes and data-bound grids.

4. Explain how the BOF and EOF properties are set and how they might be used in a

project.

Two handy properties of the Recordset object are BOF (beginning of file) and EOF (end of

file). The BOF property is automatically set to True when the record pointer is before the

first record in the Recordset. This happens when the first record is current and the user

chooses MovePrevious. The BOF property is also true if the Recordset is empty (contains

no records).

The EOF property is similar to BOF; it is True when the record pointer moves beyond the

last record in the Recordset, and when the Recordset is empty.

When you are doing your own navigation in code, you need to check for BOF and EOF, so

that run-time errors dont occur.

5. Which properties must be set to bind a combo to a field in a database and display a

dropdown list of the choices for that field?

To bind a combo box to a field in a database you must set the Name and Text properties as

usual. The DataSource property should be changed to the name of the data control on the

current form that is attached to the database table. The DataField property must be set to

indicate the field of the table that will be attached to the combo box. The List property

must be updated to display the list of the choices for that field.

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6. Which steps are needed to add a new record to a database?

To add a new record to a database you can use the data control's navigation buttons (rather

than your own code for navigation). Visual Basic will do the adds automatically if you set

the data control's EOFAction property to 2AddNew. When the user moves to the end of

the table and clicks the arrow for Next Record, an add operation begins. The data in all

bound controls is cleared so that new data can be entered. Then, when the user clicks oneof the arrow buttons, the Update method is automatically executed, and the new record is

written in the file.

Another approach for adding records is needed when navigation is accomplished with code

(rather than the navigation buttons on the data control). You can use a command button for

adding records. Use the Recordset's AddNew method in the click event for the command

button (example: datBooks.Recordset.AddNew). When this statement executes, all bound

controls are cleared so that the user can enter the data for the new record. After the data

fields are entered, the new record must be saved in the file. You can explicitly save it with

an Update method; or, if the user moves to another record, the Update method is

automatically executed. (example: datBooks.Recordset.Update).

7. Which steps are needed to delete a record from a database?The user should display the record to delete and click a Delete command button or menu

choice. The Delete method can then be used to delete the current record (example:

datBooks.Recordset.Delete). When a record is deleted, the current record is no longer valid.

Therefore, a Delete method must be followed by a MoveNext (or any other Move) method.

8. Which steps are needed to change the data in a database record?Updates (changes) for data that is displayed from a database will be handled automatically.

The Recordset object has an Update method, which you can use to save any changes in the

data. Most of the time, updating is automatic, since Visual Basic automatically executes

the Update method any time the user clicks one of the navigation buttons or one of the

Move methods executes. If you don't want the user to be able to change the data, you must

set the ReadOnly property of the data control to True. You can also keep the user from

making changes to the data by displaying fields in labels rather than text boxes.

9. How can you check for the user deleting the only record in a recordset?

When a record is deleted, the current record is no longer valid and the Delete method must

be followed by a MoveNext (or any other Move) method. If the record being deleted is the

last record in the table, a MoveNext causes an EOF condition. The program should then do

a MovePrevious. When the move is made to the previous record, a check must be made for

BOF just in case all of the records in the recordset have been deleted. If the recordset is

empty, a message box should display warning that all records have been deleted. Any

other desired action may then be taken for the empty recordset.

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