NiN

Builder

7/8/2021 OOPPattern

# Description

Builder is a creational design pattern, which allows constructing complex objects step by step.

  • Xây dụng 1 đối tượng phức tạp bằng cách xử dụng các đối tượng đơn giản theo từng step.
  • Các đối tượng độc lập với nhau.

# Example

Build query của mysql

interface SQLQueryFactory
{
    public function getSQLBuilder(): SQLQueryBuilder;
}
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interface SQLQueryBuilder
{
    public function select(string $table, array $fields): SQLQueryBuilder;

    public function where(string $field, string $value, string $operator = '='): SQLQueryBuilder;

    public function limit(int $start, int $offset): SQLQueryBuilder;

    // +100 other SQL syntax methods...

    public function getSQL(): string;
}
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class MySQLQueryFactory implements SQLQueryFactory
{
    public function getSQLBuilder(): SQLQueryBuilder
    {
        return new MySQLQueryBuilder();
    }
}
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class MySQLQueryBuilder implements SQLQueryBuilder
{
    protected \stdClass $query;

    protected function reset(): void
    {
        $this->query = new \stdClass();
    }

    /**
     * Build a base SELECT query.
     * @param string $table
     * @param array $fields
     * @return SQLQueryBuilder
     */
    public function select(string $table, array $fields): SQLQueryBuilder
    {
        $this->reset();
        $this->query->base = "SELECT " . implode(", ", $fields) . " FROM " . $table;
        $this->query->type = 'select';

        return $this;
    }

    /**
     * Add a WHERE condition.
     *
     * @param string $field
     * @param string $value
     * @param string $operator
     * @return SQLQueryBuilder
     * @throws \Exception
     */
    public function where(string $field, string $value, string $operator = '='): SQLQueryBuilder
    {
        if (!in_array($this->query->type, ['select', 'update', 'delete'])) {
            throw new \Exception("WHERE can only be added to SELECT, UPDATE OR DELETE");
        }
        $this->query->where[] = "$field $operator '$value'";

        return $this;
    }

    /**
     * Add a LIMIT constraint.
     *
     * @param int $start
     * @param int $offset
     * @return SQLQueryBuilder
     * @throws \Exception
     */
    public function limit(int $start, int $offset): SQLQueryBuilder
    {
        if (!in_array($this->query->type, ['select'])) {
            throw new \Exception("LIMIT can only be added to SELECT");
        }
        $this->query->limit = " LIMIT " . $start . ", " . $offset;

        return $this;
    }

    /**
     * Get the final query string.
     */
    public function getSQL(): string
    {
        $query = $this->query;
        $sql = $query->base;
        if (!empty($query->where)) {
            $sql .= " WHERE " . implode(' AND ', $query->where);
        }
        if (isset($query->limit)) {
            $sql .= $query->limit;
        }
        $sql .= ";";
        return $sql;
    }
}
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Usage:

$mysqlFactory = new MySQLQueryFactory();
$builder = $mysqlFactory->getSQLBuilder();
$usersQuery = $builder
    ->select('users', ['*'])
    ->where('active', true)
    ->limit(0, 10)
    ->getSQL();
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  • Create query theo từng step thay vì xử lí cùng lúc tất cả tham số (select, limit, where, ..)
  • Dễ test, maintaince.

Refer: https://refactoring.guru/design-patterns/builder/php/example#example-1