从 golang 中的 mongodb 获取数据

Question

我正在尝试使用 gopkg.in/mgo.v2 驱动程序从 golang 中的 mongodb 获取数据，数据的格式不固定，因为在几行中将包含一些其他行可能不包含的字段。

这是相同的代码

session, err := mgo.Dial("mongodb://root:root@localhost:27017/admin")
db := session.DB("test")
fmt.Println(reflect.TypeOf(db))
CheckError(err,"errpor")
result := make(map[string]string)
//query := make(map[string]string)
//query["_id"] = "3434"

err1 := db.C("mycollection").Find(nil).One(&result)
CheckError(err1,"error")
for k := range result {
    fmt.Println(k)
}

现在集合中包含的数据是 { "_id" : "3434", "0" : 1 }，但是 for 循环给出的输出为 _id ，不应该有两个键 '_id' 和 '0 ' ?还是我在这里做错了什么。

Answer 1

哦，我找到了解决方案 “结果”变量应该是 bson.M 类型，然后您可以在深入嵌套结构时进行相应的类型转换。

Answer 2

试试下面的代码。这将帮助您使用 BSON 对象从数据库中获取匹配的记录。

不要忘记在下面的代码中重命名 MongoDB 的 Database 名称和 Collection 名称。还需要相应地更改查询参数。

快乐编码...

package main

import (
    "context"
    "fmt"
    "time"

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

// This is a user defined method to close resourses.
// This method closes mongoDB connection and cancel context.
func close(client *mongo.Client, ctx context.Context, cancel context.CancelFunc) {
    defer cancel()
    defer func() {
        if err := client.Disconnect(ctx); err != nil {
            panic(err)
        }
    }()
}

// This is a user defined method that returns
// a mongo.Client, context.Context,
// context.CancelFunc and error.
// mongo.Client will be used for further database
// operation. context.Context will be used set
// deadlines for process. context.CancelFunc will
// be used to cancel context and resourse
// assositated with it.
func connect(uri string) (*mongo.Client, context.Context, context.CancelFunc, error) {
    ctx, cancel := context.WithTimeout(context.Background(),
        30*time.Second)
    client, err := mongo.Connect(ctx, options.Client().ApplyURI(uri))
    return client, ctx, cancel, err
}

// query is user defined method used to query MongoDB,
// that accepts mongo.client,context, database name,
// collection name, a query and field.

// datbase name and collection name is of type
// string. query is of type interface.
// field is of type interface, which limts
// the field being returned.

// query method returns a cursor and error.
func query(client *mongo.Client, ctx context.Context, dataBase, col string, query, field interface{}) (result *mongo.Cursor, err error) {

    // select database and collection.
    collection := client.Database(dataBase).Collection(col)

    // collection has an method Find,
    // that returns a mongo.cursor
    // based on query and field.
    result, err = collection.Find(ctx, query,
        options.Find().SetProjection(field))
    return
}

func main() {

    // Get Client, Context, CalcelFunc and err from connect method.
    client, ctx, cancel, err := connect("mongodb://localhost:27017")
    if err != nil {
        panic(err)
    }

    // Free the resource when mainn dunction is returned
    defer close(client, ctx, cancel)

    // create a filter an option of type interface,
    // that stores bjson objects.
    var filter, option interface{}

    // filter gets all document,
    // with maths field greater that 70
    filter = bson.D{
        {"_id", bson.D{{"$eq", 3434}}},
    }

    // option remove id field from all documents
    option = bson.D{{"_id", 0}}

    // call the query method with client, context,
    // database name, collection name, filter and option
    // This method returns momngo.cursor and error if any.
    cursor, err := query(client, ctx, "YourDataBaseName",
        "YourCollectioName", filter, option)
    // handle the errors.
    if err != nil {
        panic(err)
    }

    var results []bson.D

    // to get bson object from cursor,
    // returns error if any.
    if err := cursor.All(ctx, &results); err != nil {

        // handle the error
        panic(err)
    }

    // printing the result of query.
    fmt.Println("Query Reult")
    for _, doc := range results {
        fmt.Println(doc)
    }
}