BlogMapperZendDbSqlRepository.php

<?php
// In module/Blog/src/Mapper/ZendDbSqlRepository.php:

namespace Blog\Mapper; //path changed

use InvalidArgumentException;
use RuntimeException;
use Zend\Db\Adapter\AdapterInterface;
use Zend\Db\Sql\Sql;


class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * {@inheritDoc}
     */

    private $db;

    public function __construct(AdapterInterface $db)
    {
        $this->db = $db;
    }

    public function findAllPosts()
    {
        $sql    = new Sql($this->db); //changed from $this->dbAdapter
        $select = $sql->select('posts');
        $stmt   = $sql->prepareStatementForSqlObject($select);
        $result = $stmt->execute();
        return $result;
    }

    /**
     * {@inheritDoc}
     * @throws InvalidArgumentException
     * @throws RuntimeException
     */
    public function findPost($id)
    {
    }
}

/*
// In module/Blog/src/Model/ZendDbSqlRepository.php:
namespace Blog\Mapper;

use InvalidArgumentException;
use RuntimeException;
use Zend\Db\Adapter\AdapterInterface;
use Zend\Db\Sql\Sql;
use Blog\Model\PostRepositoryInterface;

class ZendDbSqlRepository implements PostRepositoryInterface
{
    /**
     * {@inheritDoc}
     */

    private $db;

    public function __construct(AdapterInterface $db)
    {
        $this->db = $db;
    }

    public function findAllPosts()
    {
        $sql    = new Sql($this->dbAdapter);
        $select = $sql->select('posts');
        $stmt   = $sql->prepareStatementForSqlObject($select);
        $result = $stmt->execute();
        return $result;
    }

    /**
     * {@inheritDoc}
     * @throws InvalidArgumentException
     * @throws RuntimeException
     */
    public function findPost($id)
    {
    }
}*/