Magento 1.9 – Fix Array to String Conversion Error in Mysql.php

How to interpret the error message

SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '2828-148-1-471' 
for key 'PRIMARY

In the case of the product attribute indexer, this means there's a constraint error while saving a record to the catalog_product_index_eav_idx table.

2828-148-1-471 refers to:

• product entity id: 2828
• attribute id: 148
• store id: 1
• value: 471

Possible origin of the problem

I'm assuming that the attribute that's causing problems is of type multiselect. A value which is linked multiple times to a product, will cause this type of error.

You can check this by executing the following query:

SELECT * FROM `catalog_product_entity_varchar` 
where entity_id = 2828 and attribute_id = 148 and store_id = 1;

I'm guessing that the id 471 will be listed multiple times in the column value. Every id should only be listed once in that column.

Are you using an importer to add product data to Magento?

Pretty simple: You're trying to cast $value as a string for the comparison, but $value is an array. If $value has some kind of value you need in it (perhaps it's nested inside an array) for the comparison, then you must process it so that it is not array.

Do this before the if statement.

var_dump($value); die;

Or

Mage::log($value); // Check var/log/system.log with logging enabled

And just examine how the data is structured in $value. Make it into a string variable.