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sort_field.go
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sort_field.go
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// Copyright 2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package sql
import (
"fmt"
"gopkg.in/src-d/go-errors.v1"
)
// SortField is a field by which a query will be sorted.
type SortField struct {
// Column to order by.
Column Expression
// Order type.
Order SortOrder
// NullOrdering defining how nulls will be ordered.
NullOrdering NullOrdering
}
type SortFields []SortField
func (sf SortFields) ToExpressions() []Expression {
es := make([]Expression, len(sf))
for i, f := range sf {
es[i] = f.Column
}
return es
}
func (sf SortFields) FromExpressions(exprs []Expression) SortFields {
var fields = make(SortFields, len(sf))
if len(exprs) != len(fields) {
panic(fmt.Sprintf("Invalid expression slice. Wanted %d elements, got %d", len(fields), len(exprs)))
}
for i, expr := range exprs {
fields[i] = SortField{
Column: expr,
NullOrdering: sf[i].NullOrdering,
Order: sf[i].Order,
}
}
return fields
}
func (s SortField) String() string {
return fmt.Sprintf("%s %s", DebugString(s.Column), s.Order)
}
func (s SortField) DebugString() string {
nullOrdering := "nullsFirst"
if s.NullOrdering == NullsLast {
nullOrdering = "nullsLast"
}
return fmt.Sprintf("%s %s %s", DebugString(s.Column), DebugString(s.Order), nullOrdering)
}
// ErrUnableSort is thrown when something happens on sorting
var ErrUnableSort = errors.NewKind("unable to sort")
// SortOrder represents the order of the sort (ascending or descending).
type SortOrder byte
const (
// Ascending order.
Ascending SortOrder = 1
// Descending order.
Descending SortOrder = 2
)
func (s SortOrder) String() string {
switch s {
case Ascending:
return "ASC"
case Descending:
return "DESC"
default:
return "invalid SortOrder"
}
}
// NullOrdering represents how to order based on null values.
type NullOrdering byte
const (
// NullsFirst puts the null values before any other values.
NullsFirst NullOrdering = iota
// NullsLast puts the null values after all other values.
NullsLast NullOrdering = 2
)