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                <?php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                namespace SilverStripe\MSSQL;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use SilverStripe\ORM\Connect\SS_Query;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use DateTime;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * A result-set from a MSSQL database.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *   | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @package mssql  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                class SQLServerQuery extends SS_Query  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * The SQLServerConnector object that created this result set.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     *   | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @var SQLServerConnector  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    private $connector;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * The internal MSSQL handle that points to the result set.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     *   | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @var resource  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    private $handle;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * Hook the result-set given into a Query class, suitable for use by sapphire.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @param SQLServerConnector $connector The database object that created this query.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @param resource $handle the internal mssql handle that is points to the resultset.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function __construct(SQLServerConnector $connector, $handle)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $this->connector = $connector;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        $this->handle = $handle;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function __destruct()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if (is_resource($this->handle)) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            sqlsrv_free_stmt($this->handle);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function seek($row)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if (!is_resource($this->handle)) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            return false;  | 
            
                            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        user_error('MSSQLQuery::seek() not supported in sqlsrv', E_USER_WARNING); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function numRecords()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if (!is_resource($this->handle)) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            return false;  | 
            
                            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        // WARNING: This will only work if the cursor type is scrollable!  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if (function_exists('sqlsrv_num_rows')) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            return sqlsrv_num_rows($this->handle);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        } else { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            user_error('MSSQLQuery::numRecords() not supported in this version of sqlsrv', E_USER_WARNING); | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    public function nextRecord()  | 
            
            
                                                        
            
                                    
            
            
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                    { | 
            
            
                                                        
            
                                    
            
            
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                        if (!is_resource($this->handle)) { | 
            
            
                                                        
            
                                    
            
            
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                            return false;  | 
            
                            
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                        }  | 
            
            
                                                        
            
                                    
            
            
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                        if ($data = sqlsrv_fetch_array($this->handle, SQLSRV_FETCH_ASSOC)) { | 
            
            
                                                        
            
                                    
            
            
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                            // special case for sqlsrv - date values are DateTime coming out of the sqlsrv drivers,  | 
            
            
                                                        
            
                                    
            
            
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                            // so we convert to the usual Y-m-d H:i:s value!  | 
            
            
                                                        
            
                                    
            
            
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                            foreach ($data as $name => $value) { | 
            
            
                                                        
            
                                    
            
            
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                                if ($value instanceof DateTime) { | 
            
            
                                                        
            
                                    
            
            
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                                    $data[$name] = $value->format('Y-m-d H:i:s'); | 
            
            
                                                        
            
                                    
            
            
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                                }  | 
            
            
                                                        
            
                                    
            
            
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                            }  | 
            
            
                                                        
            
                                    
            
            
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                            return $data;  | 
            
            
                                                        
            
                                    
            
            
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                        } else { | 
            
            
                                                        
            
                                    
            
            
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                            // Free the handle if there are no more results - sqlsrv crashes if there are too many handles  | 
            
            
                                                        
            
                                    
            
            
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                            sqlsrv_free_stmt($this->handle);  | 
            
            
                                                        
            
                                    
            
            
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                            $this->handle = null;  | 
            
            
                                                        
            
                                    
            
            
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                        }  | 
            
            
                                                        
            
                                    
            
            
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                        return false;  | 
            
                            
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                    }  | 
            
            
                                                        
            
                                    
            
            
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                }  | 
            
            
                                                        
            
                                    
            
            
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_functionexpects aPostobject, and outputs the author of the post. The base classPostreturns a simple string and outputting a simple string will work just fine. However, the child classBlogPostwhich is a sub-type ofPostinstead decided to return anobject, and is therefore violating the SOLID principles. If aBlogPostwere passed tomy_function, PHP would not complain, but ultimately fail when executing thestrtouppercall in its body.