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json_extract.go
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json_extract.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 json
import (
"fmt"
"strings"
"github.com/dolthub/go-mysql-server/sql"
"github.com/dolthub/go-mysql-server/sql/types"
)
// JSON_EXTRACT(json_doc, path[, path] ...)
//
// JSONExtract extracts data from a json document using json paths.
// https://dev.mysql.com/doc/refman/8.0/en/json-search-functions.html#function_json-extract
type JSONExtract struct {
JSON sql.Expression
Paths []sql.Expression
}
var _ sql.FunctionExpression = (*JSONExtract)(nil)
var _ sql.CollationCoercible = (*JSONExtract)(nil)
// NewJSONExtract creates a new JSONExtract UDF.
func NewJSONExtract(args ...sql.Expression) (sql.Expression, error) {
if len(args) < 2 {
return nil, sql.ErrInvalidArgumentNumber.New("JSON_EXTRACT", 2, len(args))
}
return &JSONExtract{args[0], args[1:]}, nil
}
// FunctionName implements sql.FunctionExpression
func (j *JSONExtract) FunctionName() string {
return "json_extract"
}
// Description implements sql.FunctionExpression
func (j *JSONExtract) Description() string {
return "returns data from JSON document"
}
// Resolved implements the sql.Expression interface.
func (j *JSONExtract) Resolved() bool {
for _, p := range j.Paths {
if !p.Resolved() {
return false
}
}
return j.JSON.Resolved()
}
// Type implements the sql.Expression interface.
func (j *JSONExtract) Type() sql.Type { return types.JSON }
// CollationCoercibility implements the interface sql.CollationCoercible.
func (*JSONExtract) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
return ctx.GetCharacterSet().BinaryCollation(), 2
}
// Eval implements the sql.Expression interface.
func (j *JSONExtract) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
span, ctx := ctx.Span("function.JSONExtract")
defer span.End()
js, err := j.JSON.Eval(ctx, row)
if err != nil {
return nil, err
}
// sql NULLs, should result in sql NULLs.
if js == nil {
return nil, err
}
js, _, err = types.JSON.Convert(js)
if err != nil {
return nil, err
}
searchable, ok := js.(sql.JSONWrapper)
if !ok {
return fmt.Errorf("expected types.JSONValue, found: %T", js), nil
}
var results = make([]sql.JSONWrapper, len(j.Paths))
for i, p := range j.Paths {
path, err := p.Eval(ctx, row)
if err != nil {
return nil, err
}
path, _, err = types.LongText.Convert(path)
if err != nil {
return nil, err
}
results[i], err = types.LookupJSONValue(searchable, path.(string))
if err != nil {
return nil, fmt.Errorf("failed to extract from expression '%s'; %s", j.JSON.String(), err.Error())
}
}
if len(results) == 1 {
return results[0], nil
}
return types.ConcatenateJSONValues(ctx, results...)
}
// IsNullable implements the sql.Expression interface.
func (j *JSONExtract) IsNullable() bool {
for _, p := range j.Paths {
if p.IsNullable() {
return true
}
}
return j.JSON.IsNullable()
}
// Children implements the sql.Expression interface.
func (j *JSONExtract) Children() []sql.Expression {
return append([]sql.Expression{j.JSON}, j.Paths...)
}
// WithChildren implements the Expression interface.
func (j *JSONExtract) WithChildren(children ...sql.Expression) (sql.Expression, error) {
return NewJSONExtract(children...)
}
func (j *JSONExtract) String() string {
children := j.Children()
var parts = make([]string, len(children))
for i, c := range children {
parts[i] = c.String()
}
return fmt.Sprintf("json_extract(%s)", strings.Join(parts, ", "))
}
// IsUnsupported implements sql.UnsupportedFunctionStub
func (j JSONExtract) IsUnsupported() bool {
return false
}