How to query mongo in golang

Golang is an open source programming language that is widely used in cloud computing, networks, distributed systems and other fields. MongoDB is a high-performance, scalable, document storage-oriented database that is favored by many developers. This article will introduce how to use Golang to query the MongoDB database.

1. Install the database driver

Before using Golang to connect to MongoDB, you need to install the Go language driver of MongoDB. It can be installed by executing the following command:

go get gopkg.in/mgo.v2

The name of this Go language driver is "mgo", which allows us to pass Go programs operate MongoDB databases.

2. Connect to MongoDB database

Before starting to query MongoDB, you need to establish a connection with the MongoDB database. This can be achieved by the following code:

package main
import (
    "fmt"
    "gopkg.in/mgo.v2"
)
func main() {
    session, err := mgo.Dial("mongodb://localhost:27017")
    if err != nil {
        panic(err)
    }
    defer session.Close()
    // ...
}

In this code, we use the "Dial" method in the "mgo" package to connect to the MongoDB database. When calling, we need to pass it the address of the MongoDB database. In actual applications, the correct MongoDB database address needs to be passed to it.

3. Query the MongoDB database

After you have a session connected to MongoDB, you can perform query operations. In the example below, we will get all the documents from the collection named "testdb".

package main
import (
    "fmt"
    "gopkg.in/mgo.v2"
    "gopkg.in/mgo.v2/bson"
)
type Person struct {
    Name string
    Phone string
}
func main() {
    session, err := mgo.Dial("mongodb://localhost:27017")
    if err != nil {
        panic(err)
    }
    defer session.Close()
    // 获取指定数据库的集合
    c := session.DB("test").C("testdb")
    // 查询集合中的所有文档
    var result []Person
    err = c.Find(bson.M{}).All(&result)
    if err != nil {
        panic(err)
    }
    // 输出结果
    for _, v := range result {
        fmt.Println("Name:", v.Name, "Phone:", v.Phone)
    }
}

In this example, we create a structure named "Person". The "Name" and "Phone" fields of this structure are used to store data in the document. Then we will perform query operations through the "Find" and "All" methods in the "mgo" package. When performing a query operation, we use the "bson.M" function to create an empty bson object so that we can use it in the query. We then store the results in a variable of type "[]Person" and iterate over the results and output the results.

4. Conditional query

In actual queries, we usually need to filter the documents in the collection based on conditions. Here is an example query for information about a person named "Joe".

// 查询名字为“Joe”的人的信息
err = c.Find(bson.M{"Name": "Joe"}).All(&result)
if err != nil {
    panic(err)
}
// 输出结果
for _, v := range result {
    fmt.Println("Name:", v.Name, "Phone:", v.Phone)
}

In this example, we complete the query operation by passing a bson.M containing the "Name" field value of "Joe" as the query condition.

The following is an example to query the information of everyone whose phone number contains "123".

// 查询电话号码包含“123”的人的信息
err = c.Find(bson.M{"Phone": bson.M{"$regex": "123"}}).All(&result)
if err != nil {
    panic(err)
}
// 输出结果
for _, v := range result {
    fmt.Println("Name:", v.Name, "Phone:", v.Phone)
}

In this example, we complete the query operation by passing a bson.M containing the "Phone" field value "$regex:123" as the query condition. Among them, "$regex" is a special character representing a regular expression, which is used to match people whose phone numbers contain "123".

Summary

This article introduces how to use Golang to connect to MongoDB, and demonstrates how to perform simple query operations through some examples. In practical applications, the method of querying MongoDB can be adjusted according to specific needs. At the same time, Golang's excellent performance and simple-to-use syntax also provide a better choice for operating MongoDB databases.

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