vitess.io/vitess@v0.16.2/go/vt/vtgate/vindexes/null.go (about)

     1  /*
     2  Copyright 2019 The Vitess Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package vindexes
    18  
    19  import (
    20  	"bytes"
    21  	"context"
    22  
    23  	"vitess.io/vitess/go/sqltypes"
    24  	"vitess.io/vitess/go/vt/key"
    25  )
    26  
    27  var (
    28  	_        Vindex = (*Null)(nil)
    29  	nullksid        = []byte{0}
    30  )
    31  
    32  // Null defines a vindex that always return 0. It's Unique and
    33  // Functional.
    34  // This is useful for rows that always go into the first shard.
    35  // This Vindex can be used for validating an unsharded->sharded transition.
    36  // Unlike other vindexes, this one will work even for NULL input values. This
    37  // will allow you to keep MySQL auto-inc columns unchanged.
    38  type Null struct {
    39  	name string
    40  }
    41  
    42  // NewNull creates a new Null.
    43  func NewNull(name string, m map[string]string) (Vindex, error) {
    44  	return &Null{name: name}, nil
    45  }
    46  
    47  // String returns the name of the vindex.
    48  func (vind *Null) String() string {
    49  	return vind.name
    50  }
    51  
    52  // Cost returns the cost of this index as 100.
    53  func (vind *Null) Cost() int {
    54  	return 100
    55  }
    56  
    57  // IsUnique returns true since the Vindex is unique.
    58  func (vind *Null) IsUnique() bool {
    59  	return true
    60  }
    61  
    62  // NeedsVCursor satisfies the Vindex interface.
    63  func (vind *Null) NeedsVCursor() bool {
    64  	return false
    65  }
    66  
    67  // Map can map ids to key.Destination objects.
    68  func (vind *Null) Map(ctx context.Context, vcursor VCursor, ids []sqltypes.Value) ([]key.Destination, error) {
    69  	out := make([]key.Destination, 0, len(ids))
    70  	for i := 0; i < len(ids); i++ {
    71  		out = append(out, key.DestinationKeyspaceID(nullksid))
    72  	}
    73  	return out, nil
    74  }
    75  
    76  // Verify returns true if ids maps to ksids.
    77  func (vind *Null) Verify(ctx context.Context, vcursor VCursor, ids []sqltypes.Value, ksids [][]byte) ([]bool, error) {
    78  	out := make([]bool, len(ids))
    79  	for i := range ids {
    80  		out[i] = bytes.Equal(nullksid, ksids[i])
    81  	}
    82  	return out, nil
    83  }
    84  
    85  func init() {
    86  	Register("null", NewNull)
    87  }