github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/expression/column.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 expression
    16  
    17  import (
    18  	"fmt"
    19  
    20  	"github.com/vescale/zgraph/datum"
    21  	"github.com/vescale/zgraph/parser/model"
    22  	"github.com/vescale/zgraph/stmtctx"
    23  	"github.com/vescale/zgraph/types"
    24  )
    25  
    26  var _ Expression = &Column{}
    27  
    28  type Column struct {
    29  	Index int
    30  	Name  model.CIStr
    31  	Type  types.T
    32  }
    33  
    34  func (c *Column) String() string {
    35  	return c.Name.O
    36  }
    37  
    38  func (c *Column) ReturnType() types.T {
    39  	return c.Type
    40  }
    41  
    42  func (c *Column) Eval(stmtCtx *stmtctx.Context, input datum.Row) (datum.Datum, error) {
    43  	if c.Index >= len(input) {
    44  		return nil, fmt.Errorf("column index %d out of input row length %d", c.Index, len(input))
    45  	}
    46  	return input[c.Index], nil
    47  }