github.com/hasnat/dolt/go@v0.0.0-20210628190320-9eb5d843fbb7/libraries/doltcore/schema/alterschema/dropcolumn.go (about)

     1  // Copyright 2019 Dolthub, Inc.
     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 alterschema
    16  
    17  import (
    18  	"context"
    19  	"errors"
    20  	"fmt"
    21  
    22  	"github.com/dolthub/dolt/go/libraries/doltcore/doltdb"
    23  	"github.com/dolthub/dolt/go/libraries/doltcore/schema"
    24  )
    25  
    26  var ErrKeylessAltTbl = errors.New("schema alterations not supported for keyless tables")
    27  
    28  // DropColumn drops a column from a table, and removes its associated cell values
    29  func DropColumn(ctx context.Context, tbl *doltdb.Table, colName string, foreignKeys []doltdb.ForeignKey) (*doltdb.Table, error) {
    30  	if tbl == nil {
    31  		panic("invalid parameters")
    32  	}
    33  
    34  	sch, err := tbl.GetSchema(ctx)
    35  	if err != nil {
    36  		return nil, err
    37  	}
    38  
    39  	if schema.IsKeyless(sch) {
    40  		return nil, ErrKeylessAltTbl
    41  	}
    42  
    43  	var dropTag uint64
    44  	if col, ok := sch.GetAllCols().GetByName(colName); !ok {
    45  		return nil, schema.ErrColNotFound
    46  	} else if col.IsPartOfPK {
    47  		return nil, errors.New("Cannot drop column in primary key")
    48  	} else {
    49  		dropTag = col.Tag
    50  	}
    51  
    52  	for _, foreignKey := range foreignKeys {
    53  		for _, fkTag := range foreignKey.TableColumns {
    54  			if dropTag == fkTag {
    55  				return nil, fmt.Errorf("cannot drop column `%s` as it is used in foreign key `%d`", colName, dropTag)
    56  			}
    57  		}
    58  		for _, fkTag := range foreignKey.ReferencedTableColumns {
    59  			if dropTag == fkTag {
    60  				return nil, fmt.Errorf("cannot drop column `%s` as it is used in foreign key `%d`", colName, dropTag)
    61  			}
    62  		}
    63  	}
    64  
    65  	for _, index := range sch.Indexes().IndexesWithColumn(colName) {
    66  		_, err = sch.Indexes().RemoveIndex(index.Name())
    67  		if err != nil {
    68  			return nil, err
    69  		}
    70  		tbl, err = tbl.DeleteIndexRowData(ctx, index.Name())
    71  		if err != nil {
    72  			return nil, err
    73  		}
    74  	}
    75  
    76  	cols := make([]schema.Column, 0)
    77  	err = sch.GetAllCols().Iter(func(tag uint64, col schema.Column) (stop bool, err error) {
    78  		if col.Name != colName {
    79  			cols = append(cols, col)
    80  		}
    81  		return false, nil
    82  	})
    83  
    84  	if err != nil {
    85  		return nil, err
    86  	}
    87  
    88  	colColl := schema.NewColCollection(cols...)
    89  	newSch, err := schema.SchemaFromCols(colColl)
    90  	if err != nil {
    91  		return nil, err
    92  	}
    93  	newSch.Indexes().AddIndex(sch.Indexes().AllIndexes()...)
    94  
    95  	return tbl.UpdateSchema(ctx, newSch)
    96  }