class Update

class Update extends Query implements ConditionInterface {
    use QueryConditionTrait;
    
    /**
     * The table to update.
     *
     * @var string
     */
    protected $table;
    
    /**
     * An array of fields that will be updated.
     *
     * @var array
     */
    protected $fields = [];
    
    /**
     * An array of values to update to.
     *
     * @var array
     */
    protected $arguments = [];
    
    /**
     * Array of fields to update to an expression in case of a duplicate record.
     *
     * This variable is a nested array in the following format:
     * @code
     * <some field> => array(
     *  'condition' => <condition to execute, as a string>,
     *  'arguments' => <array of arguments for condition, or NULL for none>,
     * );
     * @endcode
     *
     * @var array
     */
    protected $expressionFields = [];
    
    /**
     * Constructs an Update query object.
     *
     * @param \Drupal\Core\Database\Connection $connection
     *   A Connection object.
     * @param string $table
     *   Name of the table to associate with this query.
     * @param array $options
     *   Array of database options.
     */
    public function __construct(Connection $connection, $table, array $options = []) {
        $options['return'] = Database::RETURN_AFFECTED;
        parent::__construct($connection, $options);
        $this->table = $table;
        $this->condition = $this->connection
            ->condition('AND');
    }
    
    /**
     * Adds a set of field->value pairs to be updated.
     *
     * @param $fields
     *   An associative array of fields to write into the database. The array keys
     *   are the field names and the values are the values to which to set them.
     *
     * @return $this
     *   The called object.
     */
    public function fields(array $fields) {
        $this->fields = $fields;
        return $this;
    }
    
    /**
     * Specifies fields to be updated as an expression.
     *
     * Expression fields are cases such as counter=counter+1. This method takes
     * precedence over fields().
     *
     * @param $field
     *   The field to set.
     * @param $expression
     *   The field will be set to the value of this expression. This parameter
     *   may include named placeholders.
     * @param $arguments
     *   If specified, this is an array of key/value pairs for named placeholders
     *   corresponding to the expression.
     *
     * @return $this
     *   The called object.
     */
    public function expression($field, $expression, array $arguments = NULL) {
        $this->expressionFields[$field] = [
            'expression' => $expression,
            'arguments' => $arguments,
        ];
        return $this;
    }
    
    /**
     * Executes the UPDATE query.
     *
     * @return
     *   The number of rows matched by the update query. This includes rows that
     *   actually didn't have to be updated because the values didn't change.
     */
    public function execute() {
        // Expressions take priority over literal fields, so we process those first
        // and remove any literal fields that conflict.
        $fields = $this->fields;
        $update_values = [];
        foreach ($this->expressionFields as $field => $data) {
            if (!empty($data['arguments'])) {
                $update_values += $data['arguments'];
            }
            if ($data['expression'] instanceof SelectInterface) {
                $data['expression']->compile($this->connection, $this);
                $update_values += $data['expression']->arguments();
            }
            unset($fields[$field]);
        }
        // Because we filter $fields the same way here and in __toString(), the
        // placeholders will all match up properly.
        $max_placeholder = 0;
        foreach ($fields as $value) {
            $update_values[':db_update_placeholder_' . $max_placeholder++] = $value;
        }
        if (count($this->condition)) {
            $this->condition
                ->compile($this->connection, $this);
            $update_values = array_merge($update_values, $this->condition
                ->arguments());
        }
        return $this->connection
            ->query((string) $this, $update_values, $this->queryOptions);
    }
    
    /**
     * Implements PHP magic __toString method to convert the query to a string.
     *
     * @return string
     *   The prepared statement.
     */
    public function __toString() {
        // Create a sanitized comment string to prepend to the query.
        $comments = $this->connection
            ->makeComment($this->comments);
        // Expressions take priority over literal fields, so we process those first
        // and remove any literal fields that conflict.
        $fields = $this->fields;
        $update_fields = [];
        foreach ($this->expressionFields as $field => $data) {
            if ($data['expression'] instanceof SelectInterface) {
                // Compile and cast expression subquery to a string.
                $data['expression']->compile($this->connection, $this);
                $data['expression'] = ' (' . $data['expression'] . ')';
            }
            $update_fields[] = $this->connection
                ->escapeField($field) . '=' . $data['expression'];
            unset($fields[$field]);
        }
        $max_placeholder = 0;
        foreach ($fields as $field => $value) {
            $update_fields[] = $this->connection
                ->escapeField($field) . '=:db_update_placeholder_' . $max_placeholder++;
        }
        $query = $comments . 'UPDATE {' . $this->connection
            ->escapeTable($this->table) . '} SET ' . implode(', ', $update_fields);
        if (count($this->condition)) {
            $this->condition
                ->compile($this->connection, $this);
            // There is an implicit string cast on $this->condition.
            $query .= "\nWHERE " . $this->condition;
        }
        return $query;
    }

}