Method FindInBatches

finisher_api.go:186–256

FindInBatches finds all records in batches of batchSize

(dest interface{}, batchSize int, fc func(tx *DB, batch int) error)

// FindInBatches finds all records in batches of batchSize
func (db *DB) FindInBatches(dest interface{}, batchSize int, fc func(tx *DB, batch int) error) *DB {
	var (
		tx = db.Order(clause.OrderByColumn{
			Column: clause.Column{Table: clause.CurrentTable, Name: clause.PrimaryKey},
		}).Session(&Session{})
		queryDB      = tx
		rowsAffected int64
		batch        int
	)

	// user specified offset or limit
	var totalSize int
	if c, ok := tx.Statement.Clauses["LIMIT"]; ok {
		if limit, ok := c.Expression.(clause.Limit); ok {
			if limit.Limit != nil {
				totalSize = *limit.Limit
			}

			if totalSize > 0 && batchSize > totalSize {
				batchSize = totalSize
			}

			// reset to offset to 0 in next batch
			tx = tx.Offset(-1).Session(&Session{})
		}
	}

	for {
		result := queryDB.Limit(batchSize).Find(dest)
		rowsAffected += result.RowsAffected
		batch++

		if result.Error == nil && result.RowsAffected != 0 {
			fcTx := result.Session(&Session{NewDB: true})
			fcTx.RowsAffected = result.RowsAffected
			tx.AddError(fc(fcTx, batch))
		} else if result.Error != nil {
			tx.AddError(result.Error)
		}

		if tx.Error != nil || int(result.RowsAffected) < batchSize {
			break
		}

		if totalSize > 0 {
			if totalSize <= int(rowsAffected) {
				break
			}
			if totalSize/batchSize == batch {
				batchSize = totalSize % batchSize
			}
		}

		// Optimize for-break
		resultsValue := reflect.Indirect(reflect.ValueOf(dest))
		if result.Statement.Schema.PrioritizedPrimaryField == nil {
			tx.AddError(ErrPrimaryKeyRequired)
			break