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transform.go
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transform.go
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package dataset
import (
"sync"
)
import (
"github.com/pkg/errors"
)
import (
"github.com/arana-db/arana/pkg/proto"
)
var _ proto.Dataset = (*TransformDataset)(nil)
type (
FieldsFunc func([]proto.Field) []proto.Field
TransformFunc func(proto.Row) (proto.Row, error)
)
type TransformDataset struct {
proto.Dataset
FieldsGetter FieldsFunc
Transform TransformFunc
actualFieldsOnce sync.Once
actualFields []proto.Field
actualFieldsFailure error
}
func (td *TransformDataset) Fields() ([]proto.Field, error) {
td.actualFieldsOnce.Do(func() {
origin, err := td.Dataset.Fields()
if err != nil {
td.actualFieldsFailure = err
return
}
if td.FieldsGetter == nil {
td.actualFields = origin
return
}
td.actualFields = td.FieldsGetter(origin)
})
return td.actualFields, td.actualFieldsFailure
}
func (td *TransformDataset) Next() (proto.Row, error) {
if td.Transform == nil {
return td.Dataset.Next()
}
var (
row proto.Row
err error
)
if row, err = td.Dataset.Next(); err != nil {
return nil, err
}
if row, err = td.Transform(row); err != nil {
return nil, errors.Wrap(err, "failed to transform dataset")
}
return row, nil
}