With MongoDB, how to convert between types of decimal128 and decimal.Decimal?

[shanweie]

registry := bson.NewRegistry()
registry.RegisterTypeEncoder(reflect.TypeOf(decimal.Decimal{}), &mongo.MongoDecimal{})

conn := mon.MustNewModel(url, db, collection, opts)

怎么设置opts，使用registry自动互转

[POABOB]

Mongo Options 的原始碼在這裡：https://github.com/zeromicro/go-zero/blob/master/core/stores/mon/options.go

import (
    "reflect"

    "go.mongodb.org/mongo-driver/bson"
    // 引入 go mongo-driver
    mopt "go.mongodb.org/mongo-driver/mongo/options"
    "github.com/zeromicro/go-zero/core/stores/mon"
)

registry := bson.NewRegistry()
registry.RegisterTypeEncoder(reflect.TypeOf(decimal.Decimal{}), &mongo.MongoDecimal{})
// 使用 SetRegistry 註冊
opts := mon.Option(mopt.SetRegistry(registry))   // opts 的 type 會是 Option，這是 go-zero 自己訂的 type
conn := mon.MustNewModel(url, db, collection, opts)

資料來源：

1. https://blog.csdn.net/u013053623/article/details/129023275
2. https://pkg.go.dev/go.mongodb.org/mongo-driver/mongo/options#ClientOptions.SetRegistry
3. https://jira.mongodb.org/browse/GODRIVER-2886

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---

The source code of Mongo Options is here: https://github.com/zeromicro/go-zero/blob/master/core/stores/mon/options.go

import (
    "reflect"

    "go.mongodb.org/mongo-driver/bson"
    //Introduce go mongo-driver
    mopt "go.mongodb.org/mongo-driver/mongo/options"
    "github.com/zeromicro/go-zero/core/stores/mon"
)

registry := bson.NewRegistry()
registry.RegisterTypeEncoder(reflect.TypeOf(decimal.Decimal{}), &mongo.MongoDecimal{})
//Register using SetRegistry
opts := mon.Option(mopt.SetRegistry(registry)) // The type of opts will be Option, which is the type set by go-zero itself
conn := mon.MustNewModel(url, db, collection, opts)

source:

1. https://blog.csdn.net/u013053623/article/details/129023275
2. https://pkg.go.dev/go.mongodb.org/mongo-driver/mongo/options#ClientOptions.SetRegistry
3. https://jira.mongodb.org/browse/GODRIVER-2886

[shanweie]

mongo-driver v1.12.1，里面没有这个mopt.SetRegistry(registry)这个方法

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---

mongo-driver v1.12.1, there is no mopt.SetRegistry(registry) method in it

[POABOB]

@kevwan Hey! I have a problem with transfering mongo decimal128 to decimal.Decimal.
There doesn't seem to be a function that can set up the mongo configuration.

Could I make a pull request to add the setRegistry function for the mongo client on https://github.com/zeromicro/go-zero/blob/master/core/stores/mon/options.go?

core/stores/mon/options.go

// WithRegistry the mon client can transfer mongo types to custom types.
func WithRegistry(registry *bsoncodec.Registry) Option {
	return func(opts *options) {
		opts.SetRegistry(registry)
	}
}

To use this function, follow the example below:

registry := bson.NewRegistry()
registry.RegisterTypeEncoder(reflect.TypeOf(decimal.Decimal{}), MongoDecimal{})
// this code
opts := mon.WithRegistry(registry)
conn := mon.MustNewModel(url, db, collection, opts)

[shanweie]

试过了还是不行，错误为： cannot decode 128-bit decimal into a decimal.Decimal

registry := bson.NewRegistry()
registry.RegisterTypeEncoder(reflect.TypeOf(decimal.Decimal{}), &mongo.MongoDecimal{})
conn := mon.MustNewModel(url, db, collection, mongo.WithRegistry(registry))

func WithRegistry(registry *bsoncodec.Registry) mon.Option {
return func(opts *mopt.ClientOptions) {
opts.SetRegistry(registry)
}
}

[shanweie]

mongo.mongoDecimal的代码为：
`
package mongo

import (
"fmt"
"github.com/shopspring/decimal"
"github.com/zeromicro/go-zero/core/stores/mon"
"go.mongodb.org/mongo-driver/bson/bsoncodec"
"go.mongodb.org/mongo-driver/bson/bsonrw"
"go.mongodb.org/mongo-driver/bson/primitive"
mopt "go.mongodb.org/mongo-driver/mongo/options"
"reflect"
)

// MongoDecimal是一个允许十进制编码的ValueCodec，Decimal128到decimal.Decimal
type MongoDecimal struct{}

var _ bsoncodec.ValueCodec = &MongoDecimal{}

func WithRegistry(registry *bsoncodec.Registry) mon.Option {
return func(opts *mopt.ClientOptions) {
opts.SetRegistry(registry)
}
}

func (dc *MongoDecimal) EncodeValue(ect bsoncodec.EncodeContext, w bsonrw.ValueWriter, value reflect.Value) error {
// 使用反射转换，值改为 decimal.Decimal.
dec, ok := value.Interface().(decimal.Decimal)
if !ok {
return fmt.Errorf("value %v to encode is not of type decimal.Decimal", value)
}

// Convert decimal.Decimal to primitive.Decimal128.
primDec, err := primitive.ParseDecimal128(dec.String())
if err != nil {
	return fmt.Errorf("error converting decimal.Decimal %v to primitive.Decimal128: %v", dec, err)
}
return w.WriteDecimal128(primDec)

}

func (dc *MongoDecimal) DecodeValue(ect bsoncodec.DecodeContext, r bsonrw.ValueReader, value reflect.Value) error {
primDec, err := r.ReadDecimal128()
if err != nil {
return fmt.Errorf("error reading primitive.Decimal128 from ValueReader: %v", err)
}

// 将primitive.Decimal128转变为Golang的decimal.Decimal.
dec, err := decimal.NewFromString(primDec.String())
if err != nil {
	return fmt.Errorf("error converting primitive.Decimal128 %v to decimal.Decimal: %v", primDec, err)
}

// 设置值为 decimal.Decimal类型数据
value.Set(reflect.ValueOf(dec))
return nil

}

`

[POABOB]

@shanweie
I found a problem that you only use registry.RegisterTypeEncoder, but there is no registry.RegisterTypeEncoder.

You have to use BOTH so that you can transfering the Decimal to MongoDecimal.

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