Refactoring Model::exists() to be independent of Model::$useTable. Fixes

 #199.

Model::exists() now makes no check whatsoever on the value of
Model::$useTable. This means that, as with a database-backed dbo,
Model::exists() will call Model::find('count') (which in turn calls
DataSource::read()) to determine if the record identified by Model::$id
already exists in the datasource.

cake/libs/model/model.php

@@ -2006,11 +2006,15 @@ function __collectForeignKeys($type = 'belongsTo') {
 /**
  * Returns true if a record with the currently set ID exists.
  *
+ * Internally calls Model::getID() to obtain the current record ID to verify,
+ * and then performs a Model::find('count') on the currently configured datasource
+ * to ascertain the existence of the record in persistent storage.
+ *
  * @return boolean True if such a record exists
  * @access public
  */
 	function exists() {
-		if ($this->getID() === false || $this->useTable === false) {
+		if ($this->getID() === false) {
 			return false;
 		}
 		$conditions = array($this->alias . '.' . $this->primaryKey => $this->getID());

cake/tests/cases/libs/model/model_integration.test.php

@@ -876,7 +876,7 @@ function testLoadModelSecondIteration() {
 	}
 
 /**
- * ensure that __exists is reset on create
+ * ensure that exists() does not persist between method calls reset on create
  *
  * @return void
  */
@@ -897,6 +897,30 @@ function testResetOfExistsOnCreate() {
 		$this->assertEqual($result['Article']['title'], 'Staying alive');
 	}
 
+/**
+ * testUseTableFalseExistsCheck method
+ *
+ * @return void
+ */
+	function testUseTableFalseExistsCheck() {
+		$this->loadFixtures('Article');
+		$Article =& new Article();
+		$Article->id = 1337;
+		$result = $Article->exists();
+		$this->assertFalse($result);
+
+		$Article->useTable = false;
+		$Article->id = null;
+		$result = $Article->exists();
+		$this->assertFalse($result);
+
+		// An article with primary key of '1' has been loaded by the fixtures.
+		$Article->useTable = false;
+		$Article->id = 1;
+		$result = $Article->exists();
+		$this->assertTrue($result);
+	}
+
 /**
  * testPluginAssociations method
  *