Why Doesn't `mgo.FindId` Find My MongoDB Document?

Finding a Document by ID with mgo

Question:

In the code example below, a record known to exist in a MongoDB collection cannot be found using the FindId method. The code returns a zero value instead. What is the issue?

type id_cookie struct {
    IdCookie int
}

func get_id_mongo() int {
    session, err := mgo.Dial("127.0.0.1")
    if err != nil {
        panic(err)
    }
    defer session.Close()

    c := session.DB("id_bag").C("id_cookie")
    data := id_cookie{}
    err2 := c.FindId(bson.ObjectIdHex("58593d1d6aace357b32bb3a1")).One(&data)
    if (err2 != nil){
        Info.Println("error")
        Info.Println(err2)
    }
    Info.Println(data)
    return data.IdCookie
}

Answer:

The issue lies in the method signature of FindId. It takes only the ID as an argument, while Find requires a map where the field name is specified as well. To fix this, use the following code:

err2 := c.FindId(bson.ObjectIdHex("58593d1d6aace357b32bb3a1")).One(&data)

// OR
err2 := c.Find(bson.M{"_id": bson.ObjectIdHex("58593d1d6aace357b32bb3a1")}).One(&data)

If no errors occur, the document has been found successfully. If the IdCookie field is still zero, it may be stored with a different name in MongoDB. Use struct tags to map it correctly:

type id_cookie struct {
    IdCookie int `bson:"myid"`
}

Additionally, it's recommended to establish a single connection to MongoDB and reuse it, rather than creating a new connection for each query. Refer to the linked discussion for more details on query performance optimization.

The above is the detailed content of Why Doesn't `mgo.FindId` Find My MongoDB Document?. For more information, please follow other related articles on the PHP Chinese website!