xorm_bulk_insert_3.go

type bulkInserter interface {
	TableName() string
	Args(int) []interface{}
	Columns() string
	Values() string
	Len() int
}

const pqArgLimit = 65535

type config struct {
	returningColumns []string
}

type Option func(*config)

func Returning(columns ...string) Option {
	return func(c *config) {
		c.returningColumns = columns
	}
}

func BulkInsert(db xorm.Interface, inserter bulkInserter, options ...Option) ([]map[string]string, error) {
	insertCount := inserter.Len()
	if insertCount == 0 {
		return nil, nil
	}
	c := &config{}
	for _, opt := range options {
		opt(c)
	}
	var results []map[string]string
	returning := ""
	// RETURNING を使用する場合はSQLと返却値を用意する
	if len(c.returningColumns) > 0 {
		returning = fmt.Sprintf(" RETURNING %s", strings.Join(c.returningColumns, ", "))
		results = make([]map[string]string, 0, insertCount)
	}
	valuesString := inserter.Values() + ","
	argCount := len(inserter.Args(0))
	// "github.com/lib/pq" の引数の上限を超えないよう分割する
	insertLimit := pqArgLimit/argCount - 1
	for start := 0; start < insertCount; start += insertLimit {
		end := start + insertLimit
		if end > insertCount {
			end = insertCount
		}

		var values strings.Builder
		values.Grow(len([]byte(valuesString)) * (end - start))
		args := make([]interface{}, 0, (end-start)*argCount)
		for i := start; i < end; i++ {
			args = append(args, inserter.Args(i)...)
			values.WriteString(valuesString)
		}
		sql := fmt.Sprintf(
			"INSERT INTO %s (%s) VALUES %s%s",
			inserter.TableName(),
			inserter.Columns(),
			strings.TrimRight(values.String(), ","),
			returning,
		)
		result, err := db.QueryString(append([]interface{}{sql}, args...)...)
		if err != nil {
			return nil, err
		}
		if len(c.returningColumns) > 0 {
			results = append(results, result...)
		}
	}

	return results, nil
}