query_executor.go

package dal

import (
	"context"
)

// QueryExecutor is a query executor that returns a reader + related helper methods.
type QueryExecutor interface {

	// QueryReader returns a reader for the given query to read records 1 by 1 sequentially.
	// The Reader.Next() method returns ErrNoMoreRecords when there are no more records.
	QueryReader(ctx context.Context, query Query) (Reader, error)

	// QueryAllRecords is a helper method that returns all records for the given query.
	// It reads reader created by QueryReader until it returns ErrNoMoreRecords.
	// If you are interested only in IDs, use like:
	//
	//		reader, err := queryExecutor.SelectReader(ctx)
	//      // handle err
	//		var ids []int
	//		ids, err = dal.SelectAllIDs[int](reader)
	QueryAllRecords(ctx context.Context, query Query) (records []Record, err error)
}

var _ QueryExecutor = (*queryExecutor)(nil)

type queryExecutor struct {
	getReader ReaderProvider
}

func (s queryExecutor) QueryReader(ctx context.Context, query Query) (Reader, error) {
	return s.getReader(ctx, query)
}

// QueryAllRecords is a helper method that for a given reader returns all records as a slice.
func (s queryExecutor) QueryAllRecords(ctx context.Context, query Query) (records []Record, err error) {
	var reader Reader
	if reader, err = s.getReader(ctx, query); err != nil {
		return
	}
	if reader == nil {
		panic("reader is nil")
	}
	return SelectAllRecords(reader)
}

// ReaderProvider is a function that returns a Reader for the given query.
type ReaderProvider = func(ctx context.Context, query Query) (reader Reader, err error)

// NewQueryExecutor creates a new query executor. This is supposed to be used by dalgo DB drivers.
func NewQueryExecutor(getReader ReaderProvider) QueryExecutor {
	if getReader == nil {
		panic("getReader is a required parameter, got nil")
	}
	return &queryExecutor{getReader: getReader}
}