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convert.go
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convert.go
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// Copyright 2020-2021 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 expression
import (
"fmt"
"strings"
"time"
"gopkg.in/src-d/go-errors.v1"
"github.com/Rock-liyi/p2pdb-store/sql"
)
// ErrConvertExpression is returned when a conversion is not possible.
var ErrConvertExpression = errors.NewKind("expression '%v': couldn't convert to %v")
const (
// ConvertToBinary is a conversion to binary.
ConvertToBinary = "binary"
// ConvertToChar is a conversion to char.
ConvertToChar = "char"
// ConvertToNChar is a conversion to nchar.
ConvertToNChar = "nchar"
// ConvertToDate is a conversion to date.
ConvertToDate = "date"
// ConvertToDatetime is a conversion to datetime.
ConvertToDatetime = "datetime"
// ConvertToDecimal is a conversion to decimal.
ConvertToDecimal = "decimal"
// ConvertToDouble is a conversion to double.
ConvertToDouble = "double"
// ConvertToJSON is a conversion to json.
ConvertToJSON = "json"
// ConvertToReal is a conversion to double.
ConvertToReal = "real"
// ConvertToSigned is a conversion to signed.
ConvertToSigned = "signed"
// ConvertToTime is a conversion to time.
ConvertToTime = "time"
// ConvertToUnsigned is a conversion to unsigned.
ConvertToUnsigned = "unsigned"
)
// Convert represent a CAST(x AS T) or CONVERT(x, T) operation that casts x expression to type T.
type Convert struct {
UnaryExpression
// Type to cast
castToType string
}
// NewConvert creates a new Convert expression.
func NewConvert(expr sql.Expression, castToType string) *Convert {
return &Convert{
UnaryExpression: UnaryExpression{Child: expr},
castToType: strings.ToLower(castToType),
}
}
// IsNullable implements the Expression interface.
func (c *Convert) IsNullable() bool {
switch c.castToType {
case ConvertToDate, ConvertToDatetime:
return true
default:
return c.Child.IsNullable()
}
}
// Type implements the Expression interface.
func (c *Convert) Type() sql.Type {
switch c.castToType {
case ConvertToBinary:
return sql.LongBlob
case ConvertToChar, ConvertToNChar:
return sql.LongText
case ConvertToDate:
return sql.Date
case ConvertToDatetime:
return sql.Datetime
case ConvertToDecimal:
//TODO: these values are completely arbitrary, we need to get the given precision/scale and store it
return sql.MustCreateDecimalType(65, 10)
case ConvertToDouble, ConvertToReal:
return sql.Float64
case ConvertToJSON:
return sql.JSON
case ConvertToSigned:
return sql.Int64
case ConvertToTime:
return sql.Time
case ConvertToUnsigned:
return sql.Uint64
default:
return sql.Null
}
}
// Name implements the Expression interface.
func (c *Convert) String() string {
return fmt.Sprintf("convert(%v, %v)", c.Child, c.castToType)
}
// WithChildren implements the Expression interface.
func (c *Convert) WithChildren(children ...sql.Expression) (sql.Expression, error) {
if len(children) != 1 {
return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 1)
}
return NewConvert(children[0], c.castToType), nil
}
// Eval implements the Expression interface.
func (c *Convert) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
val, err := c.Child.Eval(ctx, row)
if err != nil {
return nil, err
}
if val == nil {
return nil, nil
}
casted, err := convertValue(val, c.castToType)
if err != nil {
return nil, ErrConvertExpression.Wrap(err, c.String(), c.castToType)
}
return casted, nil
}
// convertValue only returns an error if converting to JSON, and returns the zero value for float types.
// Nil is returned in all other cases.
func convertValue(val interface{}, castTo string) (interface{}, error) {
switch strings.ToLower(castTo) {
case ConvertToBinary:
b, err := sql.LongBlob.Convert(val)
if err != nil {
return nil, nil
}
return b, nil
case ConvertToChar, ConvertToNChar:
s, err := sql.LongText.Convert(val)
if err != nil {
return nil, nil
}
return s, nil
case ConvertToDate:
_, isTime := val.(time.Time)
_, isString := val.(string)
if !(isTime || isString) {
return nil, nil
}
d, err := sql.Date.Convert(val)
if err != nil {
return nil, nil
}
return d, nil
case ConvertToDatetime:
_, isTime := val.(time.Time)
_, isString := val.(string)
if !(isTime || isString) {
return nil, nil
}
d, err := sql.Datetime.Convert(val)
if err != nil {
return nil, nil
}
return d, nil
case ConvertToDecimal:
d, err := sql.InternalDecimalType.Convert(val)
if err != nil {
return "0", nil
}
return d, nil
case ConvertToDouble, ConvertToReal:
d, err := sql.Float64.Convert(val)
if err != nil {
return sql.Float64.Zero(), nil
}
return d, nil
case ConvertToJSON:
js, err := sql.JSON.Convert(val)
if err != nil {
return nil, err
}
return js, nil
case ConvertToSigned:
num, err := sql.Int64.Convert(val)
if err != nil {
return sql.Int64.Zero(), nil
}
return num, nil
case ConvertToTime:
t, err := sql.Time.Convert(val)
if err != nil {
return nil, nil
}
return t, nil
case ConvertToUnsigned:
num, err := sql.Uint64.Convert(val)
if err != nil {
num, err = sql.Int64.Convert(val)
if err != nil {
return sql.Uint64.Zero(), nil
}
return uint64(num.(int64)), nil
}
return num, nil
default:
return nil, nil
}
}