[MAGETWO-1556] Export: Unable to Filter Data by Attribute With Input Type Multiple Select

 - added support for multiselect attribute for both product and customer entity

Author: php4umagento

app/code/Magento/ImportExport/Block/Adminhtml/Export/Filter.php

@@ -142,7 +142,7 @@ protected function _getMultiSelectHtmlWithValue(Attribute $attribute, $value)
         if ($attribute->getFilterOptions()) {
             $options = $attribute->getFilterOptions();
         } else {
-            $options = $attribute->getSource()->getAllOptions(false);
+            $options = $attribute->getSource()->getAllOptions();
 
             foreach ($options as $key => $optionParams) {
                 if ('' === $optionParams['value']) {
@@ -151,12 +151,13 @@ protected function _getMultiSelectHtmlWithValue(Attribute $attribute, $value)
                 }
             }
         }
+
         if ($size = count($options)) {
             $arguments = [
                 'name' => $this->getFilterElementName($attribute->getAttributeCode()) . '[]',
                 'id' => $this->getFilterElementId($attribute->getAttributeCode()),
                 'class' => 'multiselect multiselect-export-filter',
-                'extra_params' => 'multiple="multiple" size="' . ($size > 5 ? 5 : ($size < 2 ? 2 : $size)),
+                'extra_params' => 'multiple="multiple" size="' . ($size > 5 ? 5 : ($size < 2 ? 2 : $size)) . '"',
             ];
             /** @var $selectBlock \Magento\Framework\View\Element\Html\Select */
             $selectBlock = $this->_layout->createBlock(
@@ -364,6 +365,9 @@ public function decorateFilter($value, Attribute $row, \Magento\Framework\DataOb
             case \Magento\ImportExport\Model\Export::FILTER_TYPE_SELECT:
                 $cell = $this->_getSelectHtmlWithValue($row, $value);
                 break;
+            case \Magento\ImportExport\Model\Export::FILTER_TYPE_MULTISELECT:
+                $cell = $this->_getMultiSelectHtmlWithValue($row, $value);
+                break;
             case \Magento\ImportExport\Model\Export::FILTER_TYPE_INPUT:
                 $cell = $this->_getInputHtmlWithValue($row, $value);
                 break;

app/code/Magento/ImportExport/Model/Export.php

@@ -30,6 +30,8 @@ class Export extends \Magento\ImportExport\Model\AbstractModel
      */
     const FILTER_TYPE_SELECT = 'select';
 
+    const FILTER_TYPE_MULTISELECT ='multiselect';
+
     const FILTER_TYPE_INPUT = 'input';
 
     const FILTER_TYPE_DATE = 'date';
@@ -215,7 +217,8 @@ public function filterAttributeCollection(\Magento\Framework\Data\Collection $co
     public static function getAttributeFilterType(\Magento\Eav\Model\Entity\Attribute $attribute)
     {
         if ($attribute->usesSource() || $attribute->getFilterOptions()) {
-            return self::FILTER_TYPE_SELECT;
+            return 'multiselect' == $attribute->getFrontendInput() ?
+                self::FILTER_TYPE_MULTISELECT : self::FILTER_TYPE_SELECT;
         } elseif ('datetime' == $attribute->getBackendType()) {
             return self::FILTER_TYPE_DATE;
         } elseif ('decimal' == $attribute->getBackendType() || 'int' == $attribute->getBackendType()) {

app/code/Magento/ImportExport/Model/Export/Entity/AbstractEav.php

@@ -152,14 +152,25 @@ public function filterEntityCollection(AbstractCollection $collection)
             // filter applying
             if (isset($exportFilter[$attributeCode])) {
                 $attributeFilterType = Export::getAttributeFilterType($attribute);
-
                 if (Export::FILTER_TYPE_SELECT == $attributeFilterType) {
                     if (is_scalar($exportFilter[$attributeCode]) && trim($exportFilter[$attributeCode])) {
                         $collection->addAttributeToFilter(
                             $attributeCode,
                             ['eq' => $exportFilter[$attributeCode]]
                         );
                     }
+                } elseif (Export::FILTER_TYPE_MULTISELECT == $attributeFilterType) {
+                    if (is_array($exportFilter[$attributeCode])) {
+                        array_filter($exportFilter[$attributeCode]);
+                        if (!empty($exportFilter[$attributeCode])) {
+                            foreach ($exportFilter[$attributeCode] as $val) {
+                                $collection->addAttributeToFilter(
+                                    $attributeCode,
+                                    ['finset' => $val]
+                                );
+                            }
+                        }
+                    }
                 } elseif (Export::FILTER_TYPE_INPUT == $attributeFilterType) {
                     if (is_scalar($exportFilter[$attributeCode]) && trim($exportFilter[$attributeCode])) {
                         $collection->addAttributeToFilter(