What are the advantages and disadvantages of using the 'Nested Sets' model for storing hierarchical data in PHP?

The 'Nested Sets' model is a way of storing hierarchical data in a database using a left and right value for each node. This allows for efficient retrieval of all descendants of a node in a single query, making it ideal for applications that require frequent traversal of hierarchical data. However, updating the tree structure can be complex and resource-intensive, as it requires updating the left and right values of multiple nodes. 

// Sample PHP code snippet for implementing the 'Nested Sets' model

// Function to retrieve all descendants of a node
function getDescendants($left, $right) {
    // Query to retrieve descendants based on left and right values
    $query = "SELECT * FROM tree WHERE left_value > $left AND right_value < $right";
    
    // Execute the query and return the results
    $result = mysqli_query($connection, $query);
    return mysqli_fetch_all($result, MYSQLI_ASSOC);
}

// Function to update the left and right values of nodes when adding a new node
function updateTreeStructure($parentRight) {
    // Update left and right values of nodes greater than the parent node
    $query = "UPDATE tree SET left_value = left_value + 2 WHERE left_value > $parentRight";
    $query2 = "UPDATE tree SET right_value = right_value + 2 WHERE right_value > $parentRight";
    
    // Execute the queries to update the tree structure
    mysqli_query($connection, $query);
    mysqli_query($connection, $query2);
}

Keywords

Nested Sets hierarchical data advantages disadvantages PHP model

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