github.com/dolthub/go-mysql-server@v0.18.0/sql/expression/function/json/json_unquote.go (about)

     1  // Copyright 2020-2021 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 json
    16  
    17  import (
    18  	"fmt"
    19  	"reflect"
    20  
    21  	"github.com/dolthub/go-mysql-server/internal/strings"
    22  	"github.com/dolthub/go-mysql-server/sql"
    23  	"github.com/dolthub/go-mysql-server/sql/expression"
    24  	"github.com/dolthub/go-mysql-server/sql/types"
    25  )
    26  
    27  // JSONUnquote unquotes JSON value and returns the result as a utf8mb4 string.
    28  // Returns NULL if the argument is NULL.
    29  // An error occurs if the value starts and ends with double quotes but is not a valid JSON string literal.
    30  type JSONUnquote struct {
    31  	expression.UnaryExpression
    32  }
    33  
    34  var _ sql.FunctionExpression = (*JSONUnquote)(nil)
    35  var _ sql.CollationCoercible = (*JSONUnquote)(nil)
    36  
    37  // NewJSONUnquote creates a new JSONUnquote UDF.
    38  func NewJSONUnquote(json sql.Expression) sql.Expression {
    39  	return &JSONUnquote{expression.UnaryExpression{Child: json}}
    40  }
    41  
    42  // FunctionName implements sql.FunctionExpression
    43  func (js *JSONUnquote) FunctionName() string {
    44  	return "json_unquote"
    45  }
    46  
    47  // Description implements sql.FunctionExpression
    48  func (js *JSONUnquote) Description() string {
    49  	return "unquotes JSON value and returns the result as a utf8mb4 string."
    50  }
    51  
    52  // IsUnsupported implements sql.UnsupportedFunctionStub
    53  func (js *JSONUnquote) IsUnsupported() bool {
    54  	return false
    55  }
    56  
    57  func (js *JSONUnquote) String() string {
    58  	return fmt.Sprintf("%s(%s)", js.FunctionName(), js.Child)
    59  }
    60  
    61  // Type implements the Expression interface.
    62  func (*JSONUnquote) Type() sql.Type {
    63  	return types.LongText
    64  }
    65  
    66  // CollationCoercibility implements the interface sql.CollationCoercible.
    67  func (*JSONUnquote) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
    68  	return ctx.GetCharacterSet().BinaryCollation(), 4
    69  }
    70  
    71  // WithChildren implements the Expression interface.
    72  func (js *JSONUnquote) WithChildren(children ...sql.Expression) (sql.Expression, error) {
    73  	if len(children) != 1 {
    74  		return nil, sql.ErrInvalidChildrenNumber.New(js, len(children), 1)
    75  	}
    76  	return NewJSONUnquote(children[0]), nil
    77  }
    78  
    79  // Eval implements the Expression interface.
    80  func (js *JSONUnquote) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
    81  	json, err := js.Child.Eval(ctx, row)
    82  	if json == nil || err != nil {
    83  		return json, err
    84  	}
    85  
    86  	ex, _, err := types.LongText.Convert(json)
    87  	if err != nil {
    88  		return nil, err
    89  	}
    90  	if ex == nil {
    91  		return nil, nil
    92  	}
    93  	str, ok := ex.(string)
    94  	if !ok {
    95  		return nil, sql.ErrInvalidType.New(reflect.TypeOf(ex).String())
    96  	}
    97  
    98  	return strings.Unquote(str)
    99  }