Ttdfjt

By Default Manual Navigation Products breadcrumb looks like,

Wanted product detail page:

When I reached to product page using by search the breadcrumb looks like,

Current product detail page:

How can I get Complete Breadcrumb of the desired products even reached
by search?

You can try this one ... create an extension with this code:

app/etc/modules/My_Module.xml

<?xml version="1.0"?>
<config>
 <modules>
 <My_Module>
 <active>true</active>
 <codePool>local</codePool>
 </My_Module>
 </modules>
</config>

app/code/local/My/Module/etc/config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
 <modules>
 <My_Module>
 <version>0.0.1</version>
 </My_Module>
 </modules>
 <global>
 <models>
 <my_module>
 <class>My_Module_Model</class>
 </my_module>
 </models>
 </global>
 <frontend>
 <events>
 <catalog_controller_product_view>
 <observers>
 <add_category_to_breadcrumbs>
 <class>my_module/observer</class>
 <method>addCategoryToBreadcrumbs</method>
 </add_category_to_breadcrumbs>
 </observers>
 </catalog_controller_product_view>
 </events>
 </frontend>
</config>

app/code/local/My/Module/Model/Observer.php

class My_Module_Model_Observer extends Mage_Core_Model_Observer

 public function addCategoryToBreadcrumbs(Varien_Event_Observer $observer)
 
 if (Mage::registry('current_category')) 
 return;
 

 $product = $observer->getProduct();

 $product->setDoNotUseCategoryId(false);
 $categoryIds = $product->getCategoryIds();

 if (count($categoryIds)) 
 $categories = Mage::getModel('catalog/category')->getCollection()
 ->addAttributeToFilter('entity_id', $categoryIds)
 ->addAttributeToFilter('is_active', 1);

 $categories->getSelect()->order('level DESC')->limit(1);

 Mage::register('current_category', $categories->getFirstItem());
 
 

The easiest way is to include category URL Keys into your product URLs. The is a special setting in Magento to do this in System > Configuration > Catalog > Search Engine Optimization > Use Categories Path for Product URLs

In case this way is not ok for you, you can use a ready solution like this one: https://www.magestyapps.com/magento-extensions/advanced-breadcrumbs.html

You can add this to magento/app/code/core/Mage/Catalog/Helper/Data.php after if ($category = $this->getCategory()) ...

 if(empty($path)) 
 if ($this->getProduct()) 

 $collection = Mage::getModel('catalog/category')->getCollection()
 ->setStoreId(Mage::app()->getStore()->getId())
 ->addAttributeToSelect('name')
 ->addAttributeToSelect('is_active')
 ->addFieldToFilter('entity_id', array('in' => $this->getProduct()->getCategoryIds()));

 $categories = array();
 $cate = false;
 foreach ($collection as $category) 
 if($category->getId()) 
 $cate = $category;
 $pathInStore = $category->getPathInStore();
 $pathIds = array_reverse(explode(',', $pathInStore));
 
 
 if($cate) 
 $categories = $cate->getParentCategories();
 if($categories) 
 foreach($pathIds as $categoryId) 
 $path['category'.$categoryId] = array(
 'label' => $categories[$categoryId]->getName(),
 'link' => $this->_isCategoryLink($categoryId) ? $categories[$categoryId]->getURL() : ''
 );
 
 else 
 $path['category'] = array('label' => $cate->getName());
 
 
 
 

Just a comment to the awesome answer of @sv3n.
Let's assume we have this category structure

root > category 1 > category 2 > category 3 > category 4

A product of the category 4 can be listed in Category 1, 2, 3 or 4
If the user clicks the product in the category 2 listing the breadcrumb will be

root > category 1 > category 2 > product

So if always the complete product breadcrumb path must be shown a change is needed

 if (Mage::registry('current_category')) 
 return;
 

for

 if (Mage::registry('current_category')) 
 Mage::unregister('current_category');