在Mongo-go-driver中创建一个唯一字段

Question

I am very new to both Go and Mongodb and was writing my first rest-api with Go and Mongo. I am using mongo-go-driver and have the following Modal struct in Go

type Modal struct {
    Group     []string           `bson:"group" json:"group"`
    Hostname  string             `bson:"hostname" json:"hostname"`
    Overrides map[string]string  `bson:"overrides" json:"overrides"`
    Excludes  []string           `bson:"excludes" json:"excludes"`
}

I do not want to use the default ObjectId field provided by mongo-db as my primary key and instead would like to make the Hostname field as the primary key.

If I make the type of Hostname field as primitive.ObjectID, then the hostname would be unique but its value will be randomly generated string by mongodb and not the actual hostname string value.

So is there a way I can do this.

Answer 1

You may use a unique index to enforce / allow only distinct values of a given field, e.g.:

db.collectionname.createIndex( { "hostname": 1 }, { unique: true } )

If you want to create such index using the official MongoDB driver, this is how you can do that:

indexName, err := coll.Indexes().CreateOne(
    context.Background(),
    IndexModel{
        Keys   : bsonx.Doc{{"hostname", bsonx.Int32(1)}},
        Options: options.Index().SetUnique(true),
    },
)

But know that in MongoDB each document must have an _id property, so doing the above, documents will have an auto-generated _id field (of ObjectId type). If this doesn't bother you, you're done.

Also note that you may map Modal.Hostname to the _id field with struct tags:

type Modal struct {
    Group     []string           `bson:"group" json:"group"`
    Hostname  string             `bson:"_id" json:"hostname"`
    Overrides map[string]string  `bson:"overrides" json:"overrides"`
    Excludes  []string           `bson:"excludes" json:"excludes"`
}

And again, you're done. The downside of this solution is that the documents in MongoDB will not have a property named hostname, as it will be stored in _id.