Remove the CrossSchemaTableExpression

This change has caused regressions for a few folks. It also doesn't work
in all the scenarios that people need it to. Not having a problematic
feature is better than having a broken one.

There was a reasonable solution in the past that involved using
`$this->table('db.table_name')` this is a decent solution that makes the
cross db joins explicit.

Refs #9293
Refs #8679

src/Database/Connection.php

@@ -711,38 +711,6 @@ public function log($sql)
         $this->logger()->log($query);
     }
 
-    /**
-     * Check if cross talk is supported between two connections
-     *
-     * @param ConnectionInterface $target Connection to check cross talk with
-     *
-     * @return bool
-     */
-    public function supportsCrossWith(ConnectionInterface $target)
-    {
-        $sourceConfig = $this->config();
-        $targetConfig = $target->config();
-
-        // No need to do report cross support in case the same connection is being used
-        if ($sourceConfig['name'] === $targetConfig['name']) {
-            return false;
-        }
-
-        $configToCheck = [
-            'driver',
-            'host',
-            'port'
-        ];
-
-        foreach ($configToCheck as $config) {
-            if ((isset($sourceConfig[$config])) && ($sourceConfig[$config] !== $targetConfig[$config])) {
-                return false;
-            }
-        }
-
-        return true;
-    }
-
     /**
      * Returns a new statement object that will log the activity
      * for the passed original statement instance.

src/Database/IdentifierQuoter.php

@@ -14,7 +14,6 @@
  */
 namespace Cake\Database;
 
-use Cake\Database\Expression\CrossSchemaTableExpression;
 use Cake\Database\Expression\FieldInterface;
 use Cake\Database\Expression\IdentifierExpression;
 use Cake\Database\Expression\OrderByExpression;
@@ -93,11 +92,6 @@ public function quoteExpression($expression)
         if ($expression instanceof IdentifierExpression) {
             $this->_quoteIdentifierExpression($expression);
 
-            return;
-        }
-        if ($expression instanceof CrossSchemaTableExpression) {
-            $this->_quoteCrossSchemaTableExpression($expression);
-
             return;
         }
     }
@@ -267,20 +261,4 @@ protected function _quoteIdentifierExpression(IdentifierExpression $expression)
             $this->_driver->quoteIdentifier($expression->getIdentifier())
         );
     }
-
-    /**
-     * Quotes the cross schema table identifier
-     *
-     * @param CrossSchemaTableExpression $expression The identifier to quote
-     * @return void
-     */
-    protected function _quoteCrossSchemaTableExpression(CrossSchemaTableExpression $expression)
-    {
-        if (!$expression->schema() instanceof ExpressionInterface) {
-            $expression->schema($this->_driver->quoteIdentifier($expression->schema()));
-        }
-        if (!$expression->table() instanceof ExpressionInterface) {
-            $expression->table($this->_driver->quoteIdentifier($expression->table()));
-        }
-    }
 }

src/ORM/Association.php

@@ -16,7 +16,6 @@
 
 use Cake\Collection\Collection;
 use Cake\Core\ConventionsTrait;
-use Cake\Database\Expression\CrossSchemaTableExpression;
 use Cake\Database\Expression\IdentifierExpression;
 use Cake\Datasource\EntityInterface;
 use Cake\Datasource\ResultSetDecorator;
@@ -557,14 +556,7 @@ public function attachTo(Query $query, array $options = [])
     {
         $target = $this->target();
         $joinType = empty($options['joinType']) ? $this->joinType() : $options['joinType'];
-
         $table = $target->table();
-        if ($this->source()->connection()->supportsCrossWith($target->connection())) {
-            $table = new CrossSchemaTableExpression(
-                $target->connection()->driver()->schema(),
-                $table
-            );
-        }
 
         $options += [
             'includeFields' => true,

tests/TestCase/Database/ConnectionTest.php

@@ -987,32 +987,4 @@ public function testSchemaCollection()
         $connection->schemaCollection($schema);
         $this->assertSame($schema, $connection->schemaCollection());
     }
-
-    /**
-     * Tests supportsCrossWith
-     *
-     * @return void
-     */
-    public function testSupportsCrossWith()
-    {
-        $connection = new Connection(ConnectionManager::config('test'));
-        $targetConnection = new Connection(ConnectionManager::config('test'));
-
-        $this->assertFalse($connection->supportsCrossWith($targetConnection), 'The same connection can\'t used in cross');
-
-        $connection = new Connection(ConnectionManager::config('test'));
-        $targetConnection = new Connection(['name' => 'test2'] + ConnectionManager::config('test'));
-
-        $this->assertTrue($connection->supportsCrossWith($targetConnection), 'Cross should be supported on databases on the same server');
-
-        $connection = new Connection(ConnectionManager::config('test'));
-        $targetConnection = new Connection(['port' => 999999] + ConnectionManager::config('test'));
-
-        $this->assertFalse($connection->supportsCrossWith($targetConnection), 'Cross is not supported across different server instances');
-
-        $connection = new Connection(ConnectionManager::config('test'));
-        $targetConnection = new Connection(['host' => 'db2.example.com'] + ConnectionManager::config('test'));
-
-        $this->assertFalse($connection->supportsCrossWith($targetConnection), 'Cross is not supported across different server instances');
-    }
 }