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PHP Developer’s Dictionary IT-SC book 55 value="<? echo $CPhone ?>"> Fax: <input type="Text" name="Fax" align="LEFT" required="Yes" size="25" value="<? echo $CFax ?>"> Email: <input type="Text" name="Email" align="LEFT" required="Yes" size="59" value="<? echo $CEmail ?>"> <input type="Submit" name="Submit" value="Submit" align="MIDDLE"> </form> </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): PHP Developer’s Dictionary IT-SC book 56 <? 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> <? $conn = pg_Connect("localhost", "5432", "", "", "test"); if (!$conn) { echo "An database connection error occurred.\ n"; exit;} $result = pg_Exec($conn,"DELETE FROM contacts WHERE cid='$ID'"); if (!$result) { echo "A DELETE query error occurred.\ n"; exit;} pg_FreeResult($result); pg_Close($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 illustrated how PHP accomplishes insert, select, update, and delete queries using PHP Developer’s Dictionary IT-SC book 57 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 PHP Developer’s Dictionary IT-SC book 58 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 $conn = pg_Connect("localhost", "5432", "", "", "test"); if (!$conn) { echo "An database connection error occurred.\ n"; 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: $CID \ n";} // Commit the transaction pg_exec($conn, "commit work;"); PHP Developer’s Dictionary IT-SC book 59 // End the transaction pg_exec($conn, "end work;"); // Free the result pg_FreeResult($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), . illustrated how PHP accomplishes insert, select, update, and delete queries using PHP Developer’s Dictionary IT-SC book 57 PostgreSQL as the database. We also gave some examples of how to use PHP to. 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 Email: <? echo $CEmail ?> <a href=select .php& gt;Back to Select Page</a> </body> </html> Notice that this script