빌더 패턴

Go code

package main

import "fmt"

type Query struct {
	table  string
	wheres []string
	order  string
	limit  int
}

type QueryBuilder struct {
	q Query
}

func Select(table string) *QueryBuilder {
	return &QueryBuilder{q: Query{table: table}}
}

func (b *QueryBuilder) Where(cond string) *QueryBuilder {
	b.q.wheres = append(b.q.wheres, cond)
	return b // 체이닝
}

func (b *QueryBuilder) OrderBy(col string) *QueryBuilder {
	b.q.order = col
	return b
}

func (b *QueryBuilder) Limit(n int) *QueryBuilder {
	b.q.limit = n
	return b
}

func (b *QueryBuilder) Build() string {
	sql := "SELECT * FROM " + b.q.table
	for i, w := range b.q.wheres {
		if i == 0 { sql += " WHERE " } else { sql += " AND " }
		sql += w
	}
	if b.q.order != "" { sql += " ORDER BY " + b.q.order }
	if b.q.limit > 0 { sql += fmt.Sprintf(" LIMIT %d", b.q.limit) }
	return sql
}

func main() {
	sql := Select("users").
		Where("age > 18").
		Where("active = true").
		OrderBy("name").
		Limit(10).
		Build()
	fmt.Println(sql)
}