forked from go-rel/rel
/
iterator.go
168 lines (132 loc) · 3.06 KB
/
iterator.go
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package rel
import (
"context"
"fmt"
"io"
)
// Iterator allows iterating through all record in database in batch.
type Iterator interface {
io.Closer
Next(record interface{}) error
}
// IteratorOption is used to configure iteration behaviour, such as batch size, start id and finish id.
type IteratorOption interface {
apply(*iterator)
}
type batchSize int
func (bs batchSize) apply(i *iterator) {
i.batchSize = int(bs)
}
// String representation.
func (bs batchSize) String() string {
return fmt.Sprintf("rel.BatchSize(%d)", bs)
}
// BatchSize specifies the size of iterator batch. Defaults to 1000.
func BatchSize(size int) IteratorOption {
return batchSize(size)
}
type start []interface{}
func (s start) apply(i *iterator) {
i.start = s
}
// String representation.
func (s start) String() string {
return fmt.Sprintf("rel.Start(%s)", fmtifaces(s))
}
// Start specifies the primary value to start from (inclusive).
func Start(id ...interface{}) IteratorOption {
return start(id)
}
type finish []interface{}
func (f finish) apply(i *iterator) {
i.finish = f
}
// String representation.
func (f finish) String() string {
return fmt.Sprintf("rel.Finish(%s)", fmtifaces(f))
}
// Finish specifies the primary value to finish at (inclusive).
func Finish(id ...interface{}) IteratorOption {
return finish(id)
}
type iterator struct {
ctx context.Context
start []interface{}
finish []interface{}
batchSize int
current int
query Query
adapter Adapter
cursor Cursor
fields []string
closed bool
}
func (i *iterator) Close() error {
if !i.closed && i.cursor != nil {
i.closed = true
return i.cursor.Close()
}
return nil
}
func (i *iterator) Next(record interface{}) error {
if i.current%i.batchSize == 0 {
if err := i.fetch(i.ctx, record); err != nil {
return err
}
}
if !i.cursor.Next() {
return io.EOF
}
var (
doc = NewDocument(record)
scanners = doc.Scanners(i.fields)
)
i.current++
return i.cursor.Scan(scanners...)
}
func (i *iterator) fetch(ctx context.Context, record interface{}) error {
if i.current == 0 {
i.init(record)
} else {
i.cursor.Close()
}
i.query = i.query.Limit(i.batchSize).Offset(i.current)
cursor, err := i.adapter.Query(ctx, i.query)
if err != nil {
return err
}
fields, err := cursor.Fields()
if err != nil {
return err
}
i.cursor = cursor
i.fields = fields
return nil
}
func (i *iterator) init(record interface{}) {
var (
doc = NewDocument(record)
)
if i.query.Table == "" {
i.query.Table = doc.Table()
}
if len(i.start) > 0 {
i.query = i.query.Where(filterDocumentPrimary(doc.PrimaryFields(), i.start, FilterGteOp))
}
if len(i.finish) > 0 {
i.query = i.query.Where(filterDocumentPrimary(doc.PrimaryFields(), i.finish, FilterLteOp))
}
i.query = i.query.SortAsc(doc.PrimaryFields()...)
}
func newIterator(ctx context.Context, adapter Adapter, query Query, options []IteratorOption) Iterator {
it := &iterator{
ctx: ctx,
batchSize: 1000,
query: query,
adapter: adapter,
}
for i := range options {
options[i].apply(it)
}
return it
}