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limit.go
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limit.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 dml
import (
"context"
)
import (
"github.com/pkg/errors"
)
import (
"github.com/arana-db/arana/pkg/dataset"
"github.com/arana-db/arana/pkg/proto"
"github.com/arana-db/arana/pkg/resultx"
)
var _ proto.Plan = (*LimitPlan)(nil)
type LimitPlan struct {
ParentPlan proto.Plan
OriginOffset int64
OverwriteLimit int64
}
func (limitPlan *LimitPlan) Type() proto.PlanType {
return proto.PlanTypeQuery
}
func (limitPlan *LimitPlan) ExecIn(ctx context.Context, conn proto.VConn) (proto.Result, error) {
if limitPlan.ParentPlan == nil {
return nil, errors.New("limitPlan: ParentPlan is nil")
}
res, err := limitPlan.ParentPlan.ExecIn(ctx, conn)
if err != nil {
return nil, errors.WithStack(err)
}
ds, err := res.Dataset()
if err != nil {
return nil, errors.WithStack(err)
}
var count int64
ds = dataset.Pipe(ds, dataset.Filter(func(next proto.Row) bool {
count++
if count < limitPlan.OriginOffset {
return false
}
if count > limitPlan.OriginOffset && count <= limitPlan.OverwriteLimit {
return true
}
return false
}))
return resultx.New(resultx.WithDataset(ds)), nil
}