php小编草莓在这里为大家介绍一种常见的需求：如何从MongoDB文档中获取元素并使用Go Mongo驱动程序更新其值。MongoDB是一种流行的NoSQL数据库，而Go是一种强大的编程语言，两者的结合可以带来很多好处。在本文中，我们将探讨如何使用Go Mongo驱动程序来实现这个需求，帮助您更好地理解和应用这个技术。

问题内容

嘿，我正在使用 go.mongodb.org/mongo-driver 包来使用 golang。这是我的代码：

package src

import (
    "context"
    "fmt"
    "log"

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

var (
    client      *mongo.client
    stickerscol *mongo.collection
)

func init() {
    log.println("setting up database...")
    var err error
    client, err = mongo.connect(context.background(), options.client().applyuri(envars.dburl))
    if err != nil {
        log.fatal(err)
    }
    log.println("connected to database")
    stickerscol = client.database("stickersbot").collection("stickers")
    chatcol = client.database("stickersbot").collection("chat")
}

func changedefaultpack(userid int64, stickername string, format string) error {
    fmt.println(userid, stickername, format)
    filter := bson.m{
        "_id":                      userid,
        "stickers.stickername":     stickername,
        "stickers.stickerpacktype": format,
    }
    updateother := bson.m{
        "$set": bson.m{
            "stickers.$[elem].isdefault": false,
        },
    }
    update := bson.m{
        "$set": bson.m{
            "stickers.$.isdefault": true,
        },
    }
    arrayfilters := options.arrayfilters{
        filters: []interface{}{bson.m{"elem.stickerpacktype": format}},
    }
    updateoptions := options.update().setarrayfilters(arrayfilters)
    _, err := stickerscol.updatemany(context.todo(), filter, updateother, updateoptions)
    if err != nil {
        return err
    }
    ok, err := stickerscol.updateone(context.background(), filter, update, options.update().setupsert(true))
    if err != nil {
        return err
    }
    if ok.modifiedcount == 0 {
        fmt.println("no document matched")
        return fmt.errorf("no document matched")
    }
    return err
}

这是数据库结构：

...
{
  "_id": 1633375527,
  "stickers": [
    {
      "stickerpacktype": "static",
      "stickername": "gVtOy_1633375527_by_ChadManBot",
      "isdefault": true
    },
    {
      "stickerpacktype": "animated",
      "stickername": "zIjsa_1633375527_by_ChadManBot",
      "isdefault": true
    },
    {
      "stickerpacktype": "video",
      "stickername": "bJBle_1633375527_by_ChadManBot",
      "isdefault": true
    },
    {
      "stickerpacktype": "static",
      "stickername": "iujiw_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "video",
      "stickername": "CHnqb_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "XKJUP_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "animated",
      "stickername": "pCFlC_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "animated",
      "stickername": "jGGgt_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "animated",
      "stickername": "cTxyA_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "animated",
      "stickername": "ZfYXO_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "xJUkA_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "HIvsY_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "WIHFQ_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "OqjtE_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "QNysO_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "OrTsT_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "FzROg_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "QUBcT_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "NsZfM_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "AkxVM_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "Ddvus_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "LXfHV_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "sTaMv_1633375527_by_ChadManBot",
      "isdefault": false
    },
    {
      "stickerpacktype": "static",
      "stickername": "vppgK_1633375527_by_ChadManBot",
      "isdefault": false
    }
  ],
  "stickerpackcount": 2
}
...

我需要我的代码是找到与给定 id 和贴纸类型匹配的贴纸包列表，并将其默认值设置为 false 并将传递给 func 的包的默认值设置为 true。

基本上只是将其中一个设置为默认值，将其他设置为非默认值。有人可以解释一下为什么这个函数返回未找到文档吗？

解决方法

当有多个字段匹配时，您应该使用 $elemmatch 运算符。否则，$ 运算符不起作用。请参阅 使用多个字段匹配更新嵌入文档。

并且您不需要 updatemany 来更新单个文档中的多个数组元素。请改用 updateone。

这是基于您的代码和数据的演示：

package main

import (
    "context"
    "fmt"
    "log"

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

var (
    client      *mongo.client
    stickerscol *mongo.collection
)

func init() {
    log.println("setting up database...")
    var err error
    client, err = mongo.connect(context.background(), options.client().applyuri("mongodb://localhost"))
    if err != nil {
        log.fatal(err)
    }
    log.println("connected to database")
    stickerscol = client.database("stickersbot").collection("stickers")
}

func changedefaultpack(userid int64, stickername string, format string) error {
    fmt.println(userid, stickername, format)
    filter := bson.m{
        "_id": userid,
        "stickers": bson.m{
            "$elemmatch": bson.m{
                "stickername":     stickername,
                "stickerpacktype": format,
            },
        },
    }
    updateother := bson.m{
        "$set": bson.m{
            "stickers.$[elem].isdefault": false,
        },
    }
    arrayfilters := options.arrayfilters{
        filters: []interface{}{bson.m{"elem.stickerpacktype": format}},
    }
    updateoptions := options.update().setarrayfilters(arrayfilters)
    result, err := stickerscol.updateone(context.background(), filter, updateother, updateoptions)
    if err != nil {
        return err
    }
    log.printf("update other: %+vn", result)

    update := bson.m{
        "$set": bson.m{
            "stickers.$.isdefault": true,
        },
    }
    ok, err := stickerscol.updateone(context.background(), filter, update, options.update().setupsert(true))
    if err != nil {
        return err
    }
    log.printf("update default: %+vn", ok)
    if ok.modifiedcount == 0 {
        fmt.println("no document matched")
        return fmt.errorf("no document matched")
    }
    return err
}

func main() {
    if err := changedefaultpack(1633375527, "ddvus_1633375527_by_chadmanbot", "static"); err != nil {
        panic(err)
    }
}

运行演示，您将观察到文档发生以下更改：

--- before.json 2023-06-27 00:34:32.721978745 +0800
 after.json  2023-06-27 00:34:59.489836137 +0800
@@ -4,7 +4,7 @@
     {
       "stickerpacktype": "static",
       "stickername": "gVtOy_1633375527_by_ChadManBot",
-      "isdefault": true
+      "isdefault": false
     },
     {
       "stickerpacktype": "animated",
@@ -104,7 +104,7 @@
     {
       "stickerpacktype": "static",
       "stickername": "Ddvus_1633375527_by_ChadManBot",
-      "isdefault": false
+      "isdefault": true
     },
     {
       "stickerpacktype": "static",