为什么我不能使用Collection类型的局部变量？ [重复]

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Newbie here.

I have a struct like this

import (
    "context"
    "time"

    "go.mongodb.org/mongo-driver/mongo"
    "go.mongodb.org/mongo-driver/mongo/options"
)

type DatabaseServiceImpl struct {
    client     *Client
    collection *Collection
}

But it complaints that it cannot find Client nor Collection.

I am definitely missing something about Go. Could someone please point out.

And here is where the Collection is defined https://github.com/mongodb/mongo-go-driver/blob/master/mongo/collection.go

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