github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/executor/selection.go (about)

     1  // Copyright 2023 zGraph Authors. All rights reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package executor
    16  
    17  import (
    18  	"context"
    19  
    20  	"github.com/vescale/zgraph/datum"
    21  	"github.com/vescale/zgraph/expression"
    22  )
    23  
    24  // SelectionExec represents a selection executor.
    25  type SelectionExec struct {
    26  	baseExecutor
    27  
    28  	condition expression.Expression
    29  }
    30  
    31  func (p *SelectionExec) Next(ctx context.Context) (datum.Row, error) {
    32  	for {
    33  		row, err := p.children[0].Next(ctx)
    34  		if err != nil || row == nil {
    35  			return nil, err
    36  		}
    37  		d, err := p.condition.Eval(p.sc, row)
    38  		if err != nil {
    39  			return nil, err
    40  		}
    41  		if datum.AsBool(d) {
    42  			return row, nil
    43  		}
    44  	}
    45  }