Using postgres arrays with slices in goqu

goqu_slices.go

package goqux

import (
	"fmt"
	"github.com/doug-martin/goqu/v9"
	"strings"
)


// PGArrayExpr takes a slice of items and returns a literal expression
// with a Postgres array that can be used by goqu.
// It does this by using goqu natively and then manipulating the string
// to surround it in an array literal.
//
// To use this in a struct, you can do something like:
//
//     type MyModel struct {
//       Tags   []string        `json:"tags" db:"-"`
//       DbTags goqu.Expression `json:"-" db:"tags"`
//     }
//     body := `{"tags":["x", "y"]}`
//     m := MyModel{}
//     _ = json.Unmarshal([]byte(body), &m)
//     m.DbTags = goqux.PGArrayExpr(m.Tags)
//     sql, _, _ := goqu.Insert("modeltable").Rows(m).ToSQL()
func PGArrayExpr[T any](arr []T) goqu.Expression {
  if len(arr) == 0 {
    return goqu.L("'{}'")
  }
  lit := goqu.V(arr)
  selectSql, _, err := goqu.From(lit).ToSQL()
  if err != nil {
    panic(err)
  }
  valuesSql := strings.TrimPrefix(selectSql, "SELECT * FROM ")
  if valuesSql == selectSql {
    panic("expected go to output an (invalid) 'SELECT * FROM (x, y, z)' for the slice")
  }
  if valuesSql[0] != '(' || valuesSql[len(valuesSql)-1] != ')' {
    panic("expected goqu to output '(x, y, z)' but is missing parens")
  }
  arraySql := fmt.Sprintf("ARRAY[%s]", valuesSql[1:len(valuesSql)-1])
  return goqu.L(arraySql)
}


func ExamplePGArrayExprWithModel() {
	type MyModel struct {
		Tags   []string        `json:"tags" db:"-"`
		DbTags goqu.Expression `json:"-" db:"tags"`
	}
	body := `{"tags":["x", "y"]}`
	m := MyModel{}
	_ = json.Unmarshal([]byte(body), &m)
	m.DbTags = goqux.PGArrayExpr(m.Tags)
	sql, _, _ := goqu.Insert("modeltable").Rows(m).ToSQL()
	fmt.Println(sql)

	// Output:
	// INSERT INTO "modeltable" ("tags") VALUES (ARRAY['x', 'y'])
}