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

     1  // Copyright 2022 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  // ProjectionExec represents a projection executor.
    25  type ProjectionExec struct {
    26  	baseExecutor
    27  
    28  	exprs []expression.Expression
    29  }
    30  
    31  func (p *ProjectionExec) Next(ctx context.Context) (datum.Row, error) {
    32  	childRow, err := p.children[0].Next(ctx)
    33  	if err != nil || childRow == nil {
    34  		return nil, err
    35  	}
    36  
    37  	result := make(datum.Row, len(p.exprs))
    38  	for i, expr := range p.exprs {
    39  		d, err := expr.Eval(p.sc, childRow)
    40  		if err != nil {
    41  			return nil, err
    42  		}
    43  		result[i] = d
    44  	}
    45  	return result, nil
    46  }