Use interface const instead of magic strings for LEFT/RIGHT/INNER join types.

src/Database/Query.php

@@ -19,6 +19,7 @@ use Cake\Database\Expression\OrderClauseExpression;
 use Cake\Database\Expression\QueryExpression;
 use Cake\Database\Expression\ValuesExpression;
 use Cake\Database\Statement\CallbackStatement;
+use Cake\Datasource\QueryInterface;
 use InvalidArgumentException;
 use IteratorAggregate;
 use RuntimeException;
@@ -613,7 +614,7 @@ class Query implements ExpressionInterface, IteratorAggregate
                 $t['conditions'] = $this->newExpr()->add($t['conditions'], $types);
             }
             $alias = is_string($alias) ? $alias : null;
-            $joins[$alias ?: $i++] = $t + ['type' => 'INNER', 'alias' => $alias];
+            $joins[$alias ?: $i++] = $t + ['type' => QueryInterface::JOIN_TYPE_INNER, 'alias' => $alias];
         }
 
         if ($overwrite) {
@@ -683,7 +684,7 @@ class Query implements ExpressionInterface, IteratorAggregate
      */
     public function leftJoin($table, $conditions = [], $types = [])
     {
-        return $this->join($this->_makeJoin($table, $conditions, 'LEFT'), $types);
+        return $this->join($this->_makeJoin($table, $conditions, QueryInterface::JOIN_TYPE_LEFT), $types);
     }
 
     /**
@@ -703,7 +704,7 @@ class Query implements ExpressionInterface, IteratorAggregate
      */
     public function rightJoin($table, $conditions = [], $types = [])
     {
-        return $this->join($this->_makeJoin($table, $conditions, 'RIGHT'), $types);
+        return $this->join($this->_makeJoin($table, $conditions, QueryInterface::JOIN_TYPE_RIGHT), $types);
     }
 
     /**
@@ -723,7 +724,7 @@ class Query implements ExpressionInterface, IteratorAggregate
      */
     public function innerJoin($table, $conditions = [], $types = [])
     {
-        return $this->join($this->_makeJoin($table, $conditions, 'INNER'), $types);
+        return $this->join($this->_makeJoin($table, $conditions, QueryInterface::JOIN_TYPE_INNER), $types);
     }
 
     /**

src/Datasource/QueryInterface.php

@@ -23,6 +23,10 @@ namespace Cake\Datasource;
 interface QueryInterface
 {
 
+    const JOIN_TYPE_INNER = 'INNER';
+    const JOIN_TYPE_LEFT = 'LEFT';
+    const JOIN_TYPE_RIGHT = 'RIGHT';
+
     /**
      * Returns a key => value array representing a single aliased field
      * that can be passed directly to the select() method.

src/ORM/Association.php

@@ -19,6 +19,7 @@ use Cake\Core\App;
 use Cake\Core\ConventionsTrait;
 use Cake\Database\Expression\IdentifierExpression;
 use Cake\Datasource\EntityInterface;
+use Cake\Datasource\QueryInterface;
 use Cake\Datasource\ResultSetDecorator;
 use Cake\ORM\Locator\LocatorAwareTrait;
 use Cake\Utility\Inflector;
@@ -158,7 +159,7 @@ abstract class Association
      *
      * @var string
      */
-    protected $_joinType = 'LEFT';
+    protected $_joinType = QueryInterface::JOIN_TYPE_LEFT;
 
     /**
      * The property name that should be filled with data from the target table

src/ORM/Association/BelongsToMany.php

@@ -18,6 +18,7 @@ use Cake\Core\App;
 use Cake\Database\ExpressionInterface;
 use Cake\Database\Expression\IdentifierExpression;
 use Cake\Datasource\EntityInterface;
+use Cake\Datasource\QueryInterface;
 use Cake\ORM\Association;
 use Cake\ORM\Association\Loader\SelectWithPivotLoader;
 use Cake\ORM\Query;
@@ -55,7 +56,7 @@ class BelongsToMany extends Association
      *
      * @var string
      */
-    protected $_joinType = 'INNER';
+    protected $_joinType = QueryInterface::JOIN_TYPE_INNER;
 
     /**
      * The strategy name to be used to fetch associated records.
@@ -1120,7 +1121,7 @@ class BelongsToMany extends Association
             $name => [
                 'table' => $this->junction()->getTable(),
                 'conditions' => $conditions,
-                'type' => 'INNER'
+                'type' => QueryInterface::JOIN_TYPE_INNER
             ]
         ];
 

src/ORM/Association/HasMany.php

@@ -19,6 +19,7 @@ use Cake\Collection\Collection;
 use Cake\Database\Expression\FieldInterface;
 use Cake\Database\Expression\QueryExpression;
 use Cake\Datasource\EntityInterface;
+use Cake\Datasource\QueryInterface;
 use Cake\ORM\Association;
 use Cake\ORM\Association\DependentDeleteHelper;
 use Cake\ORM\Association\Loader\SelectLoader;
@@ -47,7 +48,7 @@ class HasMany extends Association
      *
      * @var string
      */
-    protected $_joinType = 'INNER';
+    protected $_joinType = QueryInterface::JOIN_TYPE_INNER;
 
     /**
      * The strategy name to be used to fetch associated records.

src/ORM/Behavior/TranslateBehavior.php

@@ -17,6 +17,7 @@ namespace Cake\ORM\Behavior;
 use ArrayObject;
 use Cake\Collection\Collection;
 use Cake\Datasource\EntityInterface;
+use Cake\Datasource\QueryInterface;
 use Cake\Event\Event;
 use Cake\I18n\I18n;
 use Cake\ORM\Behavior;
@@ -173,7 +174,7 @@ class TranslateBehavior extends Behavior implements PropertyMarshalInterface
             $this->_table->hasOne($name, [
                 'targetTable' => $fieldTable,
                 'foreignKey' => 'foreign_key',
-                'joinType' => $filter ? 'INNER' : 'LEFT',
+                'joinType' => $filter ? QueryInterface::JOIN_TYPE_INNER : QueryInterface::JOIN_TYPE_LEFT,
                 'conditions' => $conditions,
                 'propertyName' => $field . '_translation'
             ]);
@@ -246,7 +247,7 @@ class TranslateBehavior extends Behavior implements PropertyMarshalInterface
             );
 
             if ($changeFilter) {
-                $filter = $options['filterByCurrentLocale'] ? 'INNER' : 'LEFT';
+                $filter = $options['filterByCurrentLocale'] ? QueryInterface::JOIN_TYPE_INNER : QueryInterface::JOIN_TYPE_LEFT;
                 $contain[$name]['joinType'] = $filter;
             }
         }

src/ORM/EagerLoader.php

@@ -16,6 +16,7 @@ namespace Cake\ORM;
 
 use Cake\Database\Statement\BufferedStatement;
 use Cake\Database\Statement\CallbackStatement;
+use Cake\Datasource\QueryInterface;
 use Closure;
 use InvalidArgumentException;
 
@@ -238,7 +239,7 @@ class EagerLoader
         }
 
         if (!isset($options['joinType'])) {
-            $options['joinType'] = 'INNER';
+            $options['joinType'] = QueryInterface::JOIN_TYPE_INNER;
         }
 
         $assocs = explode('.', $assoc);

src/ORM/Query.php

@@ -573,7 +573,7 @@ class Query extends DatabaseQuery implements JsonSerializable, QueryInterface
     {
         $result = $this->getEagerLoader()
             ->setMatching($assoc, $builder, [
-                'joinType' => 'LEFT',
+                'joinType' => QueryInterface::JOIN_TYPE_LEFT,
                 'fields' => false
             ])
             ->getMatching();
@@ -622,7 +622,7 @@ class Query extends DatabaseQuery implements JsonSerializable, QueryInterface
     {
         $result = $this->getEagerLoader()
             ->setMatching($assoc, $builder, [
-                'joinType' => 'INNER',
+                'joinType' => QueryInterface::JOIN_TYPE_INNER,
                 'fields' => false
             ])
             ->getMatching();
@@ -686,7 +686,7 @@ class Query extends DatabaseQuery implements JsonSerializable, QueryInterface
     {
         $result = $this->getEagerLoader()
             ->setMatching($assoc, $builder, [
-                'joinType' => 'LEFT',
+                'joinType' => QueryInterface::JOIN_TYPE_LEFT,
                 'fields' => false,
                 'negateMatch' => true
             ])