Builder

Muammo: ko’p qismli obyektni bosqichma-bosqich qurish kerak, lekin qismlarning bir qismi ixtiyoriy. Konstruktorga o’nta argument tiqishtirish yoki har xil kombinatsiya uchun alohida konstruktor yozish noqulay.

G’oya: har bir qadam Builderning o’zini qaytaradi, shuning uchun chaqiruvlarni zanjir qilib ulash mumkin (fluent API). Oxirida Build tayyor natijani beradi.

builder.go


package main
 
import (
	"fmt"
	"strings"
)
 
type QueryBuilder struct {
	table   string
	columns []string
	where   []string
	limit   int
}
 
func NewQueryBuilder(table string) *QueryBuilder {
	return &QueryBuilder{table: table, columns: []string{"*"}}
}
 
func (b *QueryBuilder) Select(cols ...string) *QueryBuilder { b.columns = cols; return b }
func (b *QueryBuilder) Where(cond string) *QueryBuilder     { b.where = append(b.where, cond); return b }
func (b *QueryBuilder) Limit(n int) *QueryBuilder           { b.limit = n; return b }
 
func (b *QueryBuilder) Build() string {
	var sb strings.Builder
	fmt.Fprintf(&sb, "SELECT %s FROM %s", strings.Join(b.columns, ", "), b.table)
	if len(b.where) > 0 {
		fmt.Fprintf(&sb, " WHERE %s", strings.Join(b.where, " AND "))
	}
	if b.limit > 0 {
		fmt.Fprintf(&sb, " LIMIT %d", b.limit)
	}
	return sb.String()
}
 
func main() {
	sql := NewQueryBuilder("users").
		Select("id", "name", "email").
		Where("age > 18").
		Where("active = true").
		Limit(10).
		Build()
 
	fmt.Println(sql)
}


$ go run builder.go
SELECT id, name, email FROM users WHERE age > 18 AND active = true LIMIT 10

Qachon: qurilish ko’p bosqichli va tartibli bo’lganda (SQL, HTTP so’rov, hujjat). Go note: oddiy konfiguratsiya uchun Builder o’rniga ko’pincha functional options afzalroq - keyingi sahifada.

Manba / batafsil: refactoring.guru/design-patterns/builder