How to use PATCH on PHP REST API on the following scenario?

Question

I am building a rest api with basic php code and the following code updates the records for one of my table:

$conn = $this->conn;
$returnArr = array();

$query = 'UPDATE `items` SET `name` = ?, `description` = ? WHERE `itemID` = ?';
$stmt = $conn->prepare( $query );
$stmt->bind_param( 'ssi', $this->name, $this->description, $this->itemId );

$result = $stmt->execute();
if ( $result ) {
    $stmt->close();
    return true;
} else {
    $stmt->close();
    return false;
}

So, let us say the code updates the 'items' table columns: 'name and description' from the following request made from front-end:

{
    "name": "Test item",
    "description": "Test description",
    "itemId" : 1
}

Now what if I wanted my code to only update the name when I send only the name from front-end:

{
    "name": "Test item",
    "itemId" : 1
}

What currently happens is the description is updated with NULL since $this->description is null (not initialized)

How to perform patch here with just simple basic PHP logic?

Answer 1

Build the query dynamic on the fields you want to change only.

This may look a bit complicated for only 2-3 values, but if you have a large structure (many columns/fields) it is definitely worth it.

// The dynamic data
$data = json_decode('{
    "name": "Test item",
    "description": "Test description",
    "itemId" : 1
}', true);

// a list of allowed fields for the query
$allowedFields = ['name', 'description', 'itemId'];

// build a list of fields and values for the query
$fields = [];
$values = [];
$itemId = 0;

// Go thru data and check if it is in the allowed list
// Also special treatment for the itemId

foreach($data as $field => $value) {
    if(!in_array($field, $allowedFields)) continue;
    if($field == 'itemId') {
        $itemId = $value;
        continue;
    }
    $fields[] = "`$field` = ?";
    $values[] = $data[$field];
}

// Place the itemId as very last
$values[] = $itemId;

// Build the query string
$query = 'UPDATE `items` SET ' . join(', ', $fields) . ' WHERE `itemID` = ?';

// Prepare and execute with the values
$sth = $dbh->prepare($query);
$sth->execute($values);

UPDATE items SET name =?, description =? WHERE itemID =?

Answer 2

Use store procedure in mysql and call it in PHP with every inputs contains NULL. You can filter when input is null in mysql SP.

DELIMITER \\

CREATE PROCEDURE `Update_Info`(
  IN p_name varchar(64),
  IN p_description varchar(64),
  IN p_itemID INT
)
BEGIN    
  UPDATE items
  SET `name` = IF(p_name = '', `name`, p_name),
  `description` = IF(p_description = '', `description`, p_description)
  WHERE itemID = p_itemID;
END

and in php something like this:

// calling stored procedure command
$sql = 'CALL sp_takes_string_returns_table(?,?,?)';

// prepare for execution of the stored procedure
$stmt = $pdo->prepare($sql);

// pass value to the command
$stmt->bind_param( 'ssi', $this->name, $this->description, $this->itemId );