英文:
Reading documents from MongoDB with GoLang
问题
我能够读写数据库中的文档，但我遇到了一些非常奇怪的行为。
如果搜索名字为"jack"，我会得到所有的文档，而如果搜索名字为"Mike"，我只会得到一个文档，但实际上有两个。
搜索方法：
func findByFirstName(name string) {fmt.Println("looking for - ", name)client, ctx, _ := getConnection()quickstart := client.Database("ginPlay")namesCollection := quickstart.Collection("names")var p []personnameObject, err := namesCollection.Find(ctx, bson.M{"lastName": bson.D{{"$gt", name},}})if err = nameObject.All(ctx, &p); err != nil {panic(err)}for i := 0; i < len(p); i++ {fmt.Println(p[i])}}
输出结果：
looking for - JackConnected to MongoDB!{ObjectID("613b706bf47bc212c3928870") Mike Smith 25 Netflix}{ObjectID("613b706cf47bc212c3928872") Jack Jill 36 Surfing}{ObjectID("613b706ef47bc212c3928874") Jack Jill 25 Hiking}{ObjectID("613b706ff47bc212c3928876") Jack Jill 30 Snowboarding}looking for - MikeConnected to MongoDB!{ObjectID("613b706bf47bc212c3928870") Mike Smith 25 Netflix}
数据库中的内容如下：
r.GET("/addPerson", func(c *gin.Context) {c.String(http.StatusOK, "Hello World!")p1 := person{Name: "Mike", LastName: "Foo", Age: 36, Hobbies: "Development"}p2 := person{Name: "Mike", LastName: "Smith", Age: 25, Hobbies: "Netflix"}p3 := person{Name: "Jack", LastName: "Jill", Age: 36, Hobbies: "Surfing"}p4 := person{Name: "Jack", LastName: "Jill", Age: 25, Hobbies: "Hiking"}p5 := person{Name: "Jack", LastName: "Jill", Age: 30, Hobbies: "Snowboarding"}writePerson(p1)writePerson(p2)writePerson(p3)writePerson(p4)writePerson(p5)})
数据库连接：
// GetConnection - 获取到 DocumentDB 的客户端func getConnection() (*mongo.Client, context.Context, context.CancelFunc) {username := "foo"password := "pass"clusterEndpoint := "cluster0.ml6z7m.mongodb.net/db?retryWrites=true&w=majority"connectionURI := fmt.Sprintf(connectionStringTemplate, username, password, clusterEndpoint)client, err := mongo.NewClient(options.Client().ApplyURI(connectionURI))if err != nil {log.Printf("Failed to create client: %v", err)}ctx, cancel := context.WithTimeout(context.Background(), connectTimeout*time.Second)err = client.Connect(ctx)if err != nil {log.Printf("Failed to connect to cluster: %v", err)}// 强制连接以验证连接字符串err = client.Ping(ctx, nil)if err != nil {log.Printf("Failed to ping cluster: %v", err)}fmt.Println("Connected to MongoDB!")return client, ctx, cancel}
控制器：
r.GET("/mike", func(c *gin.Context) {c.String(http.StatusOK, "Mike")findByFirstName("Mike")})r.GET("/jack", func(c *gin.Context) {c.String(http.StatusOK, "Jack")findByFirstName("Jack")})
person 结构体：
type person struct {ID primitive.ObjectID `bson:"_id,omitempty"`Name string `bson:"name,omitempty"`LastName string `bson:"lastName,omitempty"`Age int `bson:"age,omitempty"`Hobbies string `bson:"hobbies,omitempty"`}
英文:
I am able to read and write documents to database but I am experiencing some very strange behavior.
If search for the name "jack" I get every document and Mike I get just one document but they're two.
search method
func findByFirstName(name string) {fmt.Println("looking for - ", name)client, ctx, _ := getConnection()quickstart := client.Database("ginPlay")namesCollection := quickstart.Collection("names")var p []personnameObject, err := namesCollection.Find(ctx, bson.M {"lastName": bson.D {{"$gt", name},}})if err = nameObject.All(ctx, &p); err != nil {panic(err)}for i := 0; i < len(p); i++ {fmt.Println(p[i])}}
output
looking for - JackConnected to MongoDB!{ObjectID("613b706bf47bc212c3928870") Mike Smith 25 Netflix}{ObjectID("613b706cf47bc212c3928872") Jack Jill 36 Surfing}{ObjectID("613b706ef47bc212c3928874") Jack Jill 25 Hiking}{ObjectID("613b706ff47bc212c3928876") Jack Jill 30 Snowboarding}looking for - MikeConnected to MongoDB!{ObjectID("613b706bf47bc212c3928870") Mike Smith 25 Netflix}
this is what is in the database
r.GET("/addPerson", func(c *gin.Context) {c.String(http.StatusOK, "Hello World!")p1 := person{Name: "Mike", LastName: "Foo", Age: 36, Hobbies: "Development"}p2 := person{Name: "Mike", LastName: "Smith", Age: 25, Hobbies: "Netflix"}p3 := person{Name: "Jack", LastName: "Jill", Age: 36, Hobbies: "Surfing"}p4 := person{Name: "Jack", LastName: "Jill", Age: 25, Hobbies: "Hiking"}p5 := person{Name: "Jack", LastName: "Jill", Age: 30, Hobbies: "Snowboarding"}writePerson(p1)writePerson(p2)writePerson(p3)writePerson(p4)writePerson(p5)})
database connection
// GetConnection - Retrieves a client to the DocumentDBfunc getConnection() (*mongo.Client, context.Context, context.CancelFunc) {username := "foo"password := "pass"clusterEndpoint := "cluster0.ml6z7m.mongodb.net/db?retryWrites=true&w=majority"connectionURI := fmt.Sprintf(connectionStringTemplate, username, password, clusterEndpoint)client, err := mongo.NewClient(options.Client().ApplyURI(connectionURI))if err != nil {log.Printf("Failed to create client: %v", err)}ctx, cancel := context.WithTimeout(context.Background(), connectTimeout * time.Second)err = client.Connect(ctx)if err != nil {log.Printf("Failed to connect to cluster: %v", err)}// Force a connection to verify our connection stringerr = client.Ping(ctx, nil)if err != nil {log.Printf("Failed to ping cluster: %v", err)}fmt.Println("Connected to MongoDB!")return client, ctx, cancel
}
controller
r.GET("/mike", func(c *gin.Context) {c.String(http.StatusOK, "Mike")findByFirstName("Mike")})r.GET("/jack", func(c *gin.Context) {c.String(http.StatusOK, "Jack")findByFirstName("Jack")})type person struct {ID primitive.ObjectID `bson:"_id,omitempty"`Name string `bson:"name,omitempty"`LastName string `bson:"lastName,omitempty"`Age int `bson:"age,omitempty"`Hobbies string `bson:"hobbies,omitempty"`}
答案1
得分: 1
findByFirstName()函数在给定的代码中通过lastName进行搜索，并对该字段执行大于（$gt）操作，与给定的name进行比较：
nameObject, err := namesCollection.Find(ctx, bson.M {"lastName": bson.D {{"$gt", name},}})
你可能犯了一个错误，想要将"lastName"更改为"name"。
只有Mike Smith被找到，因为Smith大于Mike（Mongo进行二进制字符串比较-参见这里）。同样的原因，即使对于Jack，输出也不正确；它还包括Mike Smith，因为Smith和Jill都大于Jack，但不大于Foo。
英文:
Function findByFirstName() is searching by lastName and performs greater-than ($gt) operation on that field and given name in posted code:
nameObject, err := namesCollection.Find(ctx, bson.M {"lastName": bson.D {{"$gt", name},}})
You probably made a mistake and want to change "lastName" to "name".
Only Mike Smith is found because Smith > Mike (Mongo does binary string comparison - see here). Also, even for Jack output is not correct for the very same reason; it includes also Mike Smith as both Smith and Jill are > than Jack but not Foo.
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