如何使用官方 mongo-go-driver 从 mongo 文档中过滤字段 [英] How to filter fields from a mongo document with the official mongo-go-driver

问题描述

如何使用 mongo-go-driver 过滤字段.用 findopt.Projection 试过了，但没有成功.

How can I filter fields with the mongo-go-driver. Tried it with findopt.Projection but no success.

type fields struct {
    _id int16
}

s := bson.NewDocument()
filter := bson.NewDocument(bson.EC.ObjectID("_id", starterId))

var opts []findopt.One
opts = append(opts, findopt.Projection(fields{
    _id: 0,
}))

staCon.collection.FindOne(nil, filter, opts...).Decode(s)

最后，我想取消字段_id".但文件没有改变.

In the end, I want to suppress the field "_id". But the documents didn't change.

推荐答案

随着 mongo-go 驱动程序的发展，可以使用简单的 bson.M 像这样:

As the mongo-go driver evolved, it is possible to specify a projection using a simple bson.M like this:

options.FindOne().SetProjection(bson.M{"_id": 0})

原始(旧)答案如下.

它对您不起作用的原因是字段 fields._id 未导出，因此，没有其他包可以访问它(只有声明包).

The reason why it doesn't work for you is because the field fields._id is unexported, and as such, no other package can access it (only the declaring package).

您必须使用导出的字段名称(以大写字母开头)，例如ID，并使用 struct标签将其映射到 MongoDB _id 字段，如下所示:

You must use a field name that is exported (starts with an uppercase latter), e.g. ID, and use struct tags to map it to the MongoDB _id field like this:

type fields struct {
    ID int `bson:"_id"`
}

现在使用投影执行查询:

And now to perform a query using a projection:

projection := fields{
    ID: 0,
}
result := staCon.collection.FindOne(
    nil, filter, options.FindOne().SetProjection(projection)).Decode(s)

请注意，您也可以使用 bson.Document 作为投影，不需要自己的结构体类型.例如.以下内容相同:

Note that you may also use a bson.Document as the projection, you don't need your own struct type. E.g. the following does the same:

projection := bson.NewDocument(
    bson.EC.Int32("_id", 0),
)
result := staCon.collection.FindOne(
    nil, filter, options.FindOne().SetProjection(projection)).Decode(s)

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