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// Copyright (C) MongoDB, Inc. 2017-present.
//
// 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
package mongo
import (
"context"
"errors"
"go.mongodb.org/mongo-driver/bson"
"go.mongodb.org/mongo-driver/bson/bsoncodec"
)
// ErrNoDocuments is returned by SingleResult methods when the operation that created the SingleResult did not return
// any documents.
var ErrNoDocuments = errors.New("mongo: no documents in result")
// SingleResult represents a single document returned from an operation. If the operation resulted in an error, all
// SingleResult methods will return that error. If the operation did not return any documents, all SingleResult methods
// will return ErrNoDocuments.
type SingleResult struct {
err error
cur *Cursor
rdr bson.Raw
reg *bsoncodec.Registry
}
// Decode will unmarshal the document represented by this SingleResult into v. If there was an error from the operation
// that created this SingleResult, that error will be returned. If the operation returned no documents, Decode will
// return ErrNoDocuments.
//
// If the operation was successful and returned a document, Decode will return any errors from the unmarshalling process
// without any modification. If v is nil or is a typed nil, an error will be returned.
func (sr *SingleResult) Decode(v interface{}) error {
if sr.err != nil {
return sr.err
}
if sr.reg == nil {
return bson.ErrNilRegistry
}
if sr.err = sr.setRdrContents(); sr.err != nil {
return sr.err
}
return bson.UnmarshalWithRegistry(sr.reg, sr.rdr, v)
}
// DecodeBytes will return the document represented by this SingleResult as a bson.Raw. If there was an error from the
// operation that created this SingleResult, both the result and that error will be returned. If the operation returned
// no documents, this will return (nil, ErrNoDocuments).
func (sr *SingleResult) DecodeBytes() (bson.Raw, error) {
if sr.err != nil {
return sr.rdr, sr.err
}
if sr.err = sr.setRdrContents(); sr.err != nil {
return nil, sr.err
}
return sr.rdr, nil
}
// setRdrContents will set the contents of rdr by iterating the underlying cursor if necessary.
func (sr *SingleResult) setRdrContents() error {
switch {
case sr.err != nil:
return sr.err
case sr.rdr != nil:
return nil
case sr.cur != nil:
defer sr.cur.Close(context.TODO())
if !sr.cur.Next(context.TODO()) {
if err := sr.cur.Err(); err != nil {
return err
}
return ErrNoDocuments
}
sr.rdr = sr.cur.Current
return nil
}
return ErrNoDocuments
}
// Err returns the error from the operation that created this SingleResult. If the operation was successful but did not
// return any documents, Err will return ErrNoDocuments. If the operation was successful and returned a document, Err
// will return nil.
func (sr *SingleResult) Err() error {
sr.err = sr.setRdrContents()
return sr.err
}
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