PHP Developer''''s Dictionary- P12 potx

Address: City: State: Zip: Phone: Fax: Email: Back to Select Page Notice that this script verifies that information in the database was changed by performing a sele

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value="<? echo $CPhone ?>">

Fax:

Email:

<input type="Text" name="Email" align="LEFT" required="Yes"

size="59"

value="<? echo $CEmail ?>">

</body>

</html>

This script's first task is to determine, through the CID, which record is to be edited This is done with a simple select query The result set of this query is placed into variables to be used later in the HTML form Notice that because only one record is

to be returned, we do not need to use a while loop and an array to return multiple records The returned variables are placed into the HTML input tag as the value of the field This places the information in the input field and enables the end user to edit the information

After the Submit button is pressed, the second part of this script performs the update query The form variables are passed to this script and are used to create the update query that is sent to the database

<html>

<head>

<title>Edit Record</title>

<?

$conn = pg_Connect("localhost", "5432", "", "", "test");

if (!$conn) { echo "An database connection error occurred.\ n";

exit;}

$result = pg_Exec($conn,"UPDATE contacts SET name='$FullName',

address='$Address', city='$City', state='$State', zip='$Zip', phone='$Phone', fax='$Fax', email='$Email'WHERE cid='$ID'");

if (!$result) { echo "An UPDATE query error occurred.\ n"; exit;}

$result = pg_Exec($conn,"SELECT cid, name, address, city, state, zip, phone, fax, email FROM contacts WHERE cid=$ID;");

if (!$result) { echo "A query error occurred.\ n"; exit;}

$CID = pg_Result($result, $i, "cid");

$CName = pg_Result($result, $i, "name");

$CAddress = pg_Result($result, $i, "address");

$CCity = pg_Result($result, $i, "city");

$CState = pg_Result($result, $i, "state");

$CZip = pg_Result($result, $i, "zip");

$CPhone = pg_Result($result, $i, "phone");

$CFax = pg_Result($result, $i, "fax");

$CEmail = pg_Result($result, $i, "email");

pg_FreeResult($result);

pg_Close($conn);

?>

</head>

<body>

The information has been changed to:

Full Name (Last, First MI):

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<? echo $CName ?>

Address:

<? echo $CAddress ?>

City:

<? echo $CCity ?>

State:

<? echo $CState ?>

Zip:

<? echo $CZip ?>

Phone:

<? echo $CPhone ?>

Fax:

<? echo $CFax ?>

Email:

<? echo $CEmail ?>

<a href=select.php>Back to Select Page</a>

</body>

</html>

Notice that this script verifies that information in the database was changed by performing a select query, which displays the changed information in the browser window

Delete Queries

The delete query is the last of our simple examples If the delete link is clicked from the initial select query page, the CID ID is passed to the following script:

<title>Delete Record</title>

<?

exit;}

$result = pg_Exec($conn,"DELETE FROM contacts WHERE cid='$ID'");

if (!$result) { echo "A DELETE query error occurred.\ n"; exit;}

pg_Close($conn);

?>

</head>

<body>

The record was deleted

<a href=select.php>Back to Select Page</a>

</body>

</html>

This script simply deletes the record defined by the CID from the database You can click the Back to Select Page link to verify that the record was deleted

This concludes the four functions that all database applications perform We

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PostgreSQL as the database We also gave some examples of how to use PHP to display and manipulate the information in the Web browser

Other Database Functions

Many other database functions can be performed other than the basic queries that were demonstrated earlier The PHP interface to PostgreSQL enables you to specify how the information is returned from the database You can return information as an array by using pg_Fetch_Array() or pg_Fetch_Row() You can return information as

an object by using pg_Fetch_Object() Other functions will return the size and type

of the field or column or the name or number of fields The description and use of each of these functions is included in Chapter 10, "Database Extensions." Many useful bits of information and properties can be returned through the use of these database functions A detailed description with examples of each of these functions is beyond the scope of this book, but each is fairly straightforward and should be easy

to implement

Error Messages

It is always a good idea to capture and print all error messages The PHP interface to PostgreSQL includes a function that allows for this functionality This function is

pg_errormessage() and it accepts the database connection handle and returns the string of the error This string is the text of the error message that is generated from the database back end

The following example illustrates how to use the pg_errormessage() function to return an error string The pg_Connect() function in the example attempts to connect to a database that does not exist If the function returns an error (as it does

in this case), the connection handle is used in the pg_errormessage() function to echo the string to the browser

<html>

<head>

<title>Generate an Error</title>

</head>

<body>

<?

// Generate an error connecting to a Postgres Database

$conn = pg_Connect("localhost", "5432", "", "", "testerror");

if (!$conn) { echo pg_errormessage($conn); exit;}

?>

</body>

</html>

This example prints out the following error message to the browser window:

FATAL 1: Database testerror does not exist in pg_database

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Transaction Management

As your database-enabled Web applications become bigger and more complex, you will find the need to lock tables and manage the transactions on the database to eliminate data corruption When two queries access the same tables to perform any operation other than a simple select query, there is the possibility for the data to become corrupted

The following simple example illustrates how to set up a transaction, perform the query or set of queries, and then commit the transaction If the transaction fails at any point, the entire sequence is rolled back

<html>

<head>

<title>Managing the Transaction</title>

</head>

<body>

<?

// Connect to the Postgres Database

exit;}

// Begin the Transaction

$result = pg_exec($conn, "begin work;");

if (!$result) { echo "An error occurred beginning the transaction.\ n"; exit;}

// Lock the table

$result = pg_exec($conn, "lock contacts;");

if (!$result) { echo "An error occurred locking the contacts table.\ n"; exit;}

// Insert the static values into the database

$result = pg_Exec($conn,"INSERT INTO contacts VALUES (NEXTVAL('c'), 'Test Name','Test Address','Test

City','TS','11111','111.222.3333',

'444.555.6666','me@email.com');");

if (!$result) { echo "An INSERT query error occurred.\ n"; exit;} // Get the last record inserted

$oid = pg_getlastoid($result);

if (!$oid) { echo "An OID error occurred.\ n"; exit;}

// Select the record that was last entered

$result = pg_Exec($conn,"SELECT cid FROM contacts WHERE oid=$oid;");

if (!$result) { echo "A SELECT query error occurred.\ n"; exit;}

// Place the result into the variable $CID

$CID = pg_Result($result, 0, "cid");

if (!$CID) { echo "There is a problem returning the Contact ID.\ n"; exit;}

// Print out the Contact ID

else { echo "The record was successfully entered and the Contact ID is:

$CID \ n";}

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// End the transaction

pg_exec($conn, "end work;");

// Free the result

// Close the connection

pg_Close($conn);

?>

</body>

</html>

Notice that the new portions of this insert query include a BEGIN statement that denotes the start of the transaction The transaction in this example is named work The next statement is the LOCK statement This particular statement locks the entire table while the transaction is being performed There are many types of locks—both table level and row level—that can be placed on a database while transactions are being performed A discussion of the pros and cons of each of these types of locks is beyond the scope of this book Please consult your database documentation for a description of the locks that are available

In the preceding example, the next bit of code performs the database insert and query This section of code is very elementary, but it is included for illustration purposes The next two pg_exec() statements end the transaction; the first commits the work transaction, and the second ends the transaction

Persistent Database Connections

One of the biggest performance increases that you can make to your database application is to use persistent connections The establishment of a database connection can often take 90% of the total time of the query In other words, if you can reuse database connections, your application can make all the queries 90% faster If your application is database intensive, the overall speed of the application can be affected in a positive manner by using persistent connections

The pg_pConnect() function is the mechanism that you can use to make a persistent database connection When a connection to the database is requested, PHP checks for an existing connection If one exists, PHP does not open another connection but reuses the existing connection If a connection does not exist, PHP opens one

From the user's perspective, the pg_pConnect() function works exactly the same as its nonpersistent counterpart, pg_connect()

Large Objects

Sometimes it might be necessary to store binary objects in a database PostgreSQL enables you to do this through the use of inversion of large objects This is the method used to store images, PDF files, and entire Web pages in a database The use of large objects requires the database table to be set up to accept an object identifier (OID) The create table statement looks something like this:

create table contacts (

cid int4 DEFAULT NEXTVAL('a'),

name char (50),

address char (50),

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