github.com/vescale/zgraph@v0.0.0-20230410094002-959c02d50f95/executor/simple.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/pingcap/errors"
    21  	"github.com/vescale/zgraph/datum"
    22  	"github.com/vescale/zgraph/meta"
    23  	"github.com/vescale/zgraph/parser/ast"
    24  )
    25  
    26  // SimpleExec is used to execute some simple tasks.
    27  type SimpleExec struct {
    28  	baseExecutor
    29  
    30  	done      bool
    31  	statement ast.StmtNode
    32  }
    33  
    34  func (e *SimpleExec) Next(_ context.Context) (datum.Row, error) {
    35  	if e.done {
    36  		return nil, nil
    37  	}
    38  	e.done = true
    39  
    40  	switch stmt := e.statement.(type) {
    41  	case *ast.UseStmt:
    42  		return nil, e.execUse(stmt)
    43  	default:
    44  		return nil, errors.Errorf("unknown statement: %T", e.statement)
    45  	}
    46  }
    47  
    48  func (e *SimpleExec) execUse(stmt *ast.UseStmt) error {
    49  	graph := e.sc.Catalog().Graph(stmt.GraphName.L)
    50  	if graph == nil {
    51  		return meta.ErrGraphNotExists
    52  	}
    53  
    54  	e.sc.SetCurrentGraphName(stmt.GraphName.L)
    55  
    56  	return nil
    57  }