Adding Datasource::enabled()

Allows for checking a datasource's ability to be used before attempting to connect it.
Added enabled() to all the core dbo's.
Fixes whitescreen when trying to use a non installed database driver.
Fixes #131

cake/libs/model/datasources/datasource.php

@@ -364,6 +364,16 @@ function lastNumRows($source = null) {
 	function lastAffected($source = null) {
 		return false;
 	}
+/**
+ * Check whether the conditions for the Datasource being available
+ * are satisfied.  Often used from connect() to check for support
+ * before establishing a connection.
+ *
+ * @return boolean Whether or not the Datasources conditions for use are met.
+ **/
+	function enabled() {
+		return true;
+	}
 /**
  * Returns true if the DataSource supports the given interface (method)
  *

cake/libs/model/datasources/dbo/dbo_adodb.php

@@ -102,7 +102,9 @@ function connect() {
 			$adodb_driver = substr($config['connect'], 0, $persistent);
 			$connect = 'PConnect';
 		}
-
+		if (!$this->enabled()) {
+			return false;
+		}
 		$this->_adodb = NewADOConnection($adodb_driver);
 
 		$this->_adodbDataDict = NewDataDictionary($this->_adodb, $adodb_driver);
@@ -114,6 +116,14 @@ function connect() {
 		$this->_adodbMetatyper = &$this->_adodb->execute('Select 1');
 		return $this->connected;
 	}
+/**
+ * Check that AdoDB is available.
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return function_exists('NewADOConnection');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_db2.php

@@ -136,6 +136,14 @@ function connect() {
 		}
 		return $this->connected;
 	}
+/**
+ * Check that the DB2 extension is installed/loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('ibm_db2');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_firebird.php

@@ -127,9 +127,18 @@ function connect() {
 		$connect = $config['connect'];
 
 		$this->connected = false;
+
 		$this->connection = $connect($config['host'] . ':' . $config['database'], $config['login'], $config['password']);
 		$this->connected = true;
 	}
+/**
+ * Check that the interbase extension is loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('interbase');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_mssql.php

@@ -152,6 +152,14 @@ function connect() {
 		}
 		return $this->connected;
 	}
+/**
+ * Check that MsSQL is installed/loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('mssql');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_mysql.php

@@ -388,6 +388,14 @@ function connect() {
 
 		return $this->connected;
 	}
+/**
+ * Check whether the MySQL extension is installed/loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('mysql');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_mysqli.php

@@ -83,6 +83,14 @@ function connect() {
 		}
 		return $this->connected;
 	}
+/**
+ * Check that MySQLi is installed/enabled
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('mysqli');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_odbc.php

@@ -105,6 +105,14 @@ function connect() {
 
 		return $this->connected;
 	}
+/**
+ * Check if the ODBC extension is installed/loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('odbc');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_postgres.php

@@ -122,6 +122,14 @@ function connect() {
 		}
 		return $this->connected;
 	}
+/**
+ * Check if PostgreSQL is enabled/loaded
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('pgsql');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_sqlite.php

@@ -113,6 +113,14 @@ function connect() {
 		}
 		return $this->connected;
 	}
+/**
+ * Check that SQLite is enabled/installed
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('sqlite');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo/dbo_sybase.php

@@ -102,6 +102,14 @@ function connect() {
 		$this->connected = sybase_select_db($config['database'], $this->connection);
 		return $this->connected;
 	}
+/**
+ * Check that one of the sybase extensions is installed
+ *
+ * @return boolean
+ **/
+	function enabled() {
+		return extension_loaded('sybase') || extension_loaded('sybase_ct');
+	}
 /**
  * Disconnects from database.
  *

cake/libs/model/datasources/dbo_source.php

@@ -91,7 +91,9 @@ function __construct($config = null, $autoConnect = true) {
 		}
 		parent::__construct($config);
 		$this->fullDebug = Configure::read() > 1;
-
+		if (!$this->enabled()) {
+			return false;
+		}
 		if ($autoConnect) {
 			return $this->connect();
 		} else {