将Go结构体编组为BSON以供mongoimport使用。

huangapple
go评论167阅读模式
英文:

Marshal Go Struct to BSON for mongoimport

问题

我有一个结构体切片，我想将其写入一个 BSON 文件，以便进行 mongoimport。

这是我正在做的大致想法（使用 gopkg.in/mgo.v2/bson）：

  1. type Item struct {
  2.     ID   string `bson:"_id"`
  3.     Text string `bson:"text"`
  4. }
  6. items := []Item{
  7.     {
  8.         ID:   "abc",
  9.         Text: "def",
  10.     },
  11.     {
  12.         ID:   "uvw",
  13.         Text: "xyz",
  14.     },
  15. }
  17. file, err := bson.Marshal(items)
  18. if err != nil {
  19.     fmt.Printf("Failed to marshal BSON file: '%s'", err.Error())
  20. }
  22. if err := ioutil.WriteFile("test.bson", file, 0644); err != nil {
  23.     fmt.Printf("Failed to write BSON file: '%s'", err.Error())
  24. }

这段代码可以运行并生成文件，但格式不正确 - 它看起来像这样（使用 bsondump --pretty test.bson）：

  1. {
  2.     "1": {
  3.         "_id": "abc",
  4.         "text": "def"
  5.     },
  6.     "2": {
  7.         "_id": "abc",
  8.         "text": "def"
  9.     }
  10. }

我认为它应该更像这样：

  1. {
  2.     "_id": "abc",
  3.     "text": "def"
  4. }
  5. {
  6.     "_id": "abc",
  7.     "text": "def"
  8. }

在 Go 中是否可以实现这个效果？我只是想生成一个 .bson 文件，就像你期望 mongodump 命令生成的那样，这样我就可以运行 mongoimport 命令并填充一个集合。

英文:

I have a slice of structs that I want to write to a BSON file for doing a mongoimport.

This a rough idea of what I'm doing (using gopkg.in/mgo.v2/bson):

  1. type Item struct {
  2.     ID   string `bson:"_id"`
  3.     Text string `bson:"text"`
  4. }
  6. items := []Item{
  7.     {
  8.         ID: "abc",
  9.         Text: "def",
  10.     },
  11.     {
  12.         ID: "uvw",
  13.         Text: "xyz",
  14.     },
  15. }
  17. file, err := bson.Marshal(items)
  18. if err != nil {
  19. 	fmt.Printf("Failed to marshal BSON file: '%s'", err.Error())
  20. }
  22. if err := ioutil.WriteFile("test.bson", file, 0644); err != nil {
  23. 	fmt.Printf("Failed to write BSON file: '%s'", err.Error())
  24. }

This runs and generates the file, but it's not formatted correctly - instead it looks like this (using bsondump --pretty test.bson):

  1. {
  2.     "1": {
  3.         "_id": "abc",
  4.         "text": "def"
  5.     },
  6.     "2": {
  7.         "_id": "abc",
  8.         "text": "def"
  9.     }
  10. }

When I think it should look more like:

  1. {
  2.     "_id": "abc",
  3.     "text": "def"
  4. {
  5. }
  6.     "_id": "abc",
  7.     "text": "def"
  8. }

Is this possible to do in Go? I just want to generate a .bson file that you would expect a mongodump command to produce, so that I can run mongoimport and populate a colection.

答案1

得分: 1

你想要独立的BSON文档，所以需要逐个进行编组：

  1. buf := &bytes.Buffer{}
  2. for _, item := range items {
  3. 	data, err := bson.Marshal(item)
  4. 	if err != nil {
  5. 		fmt.Printf("无法编组BSON项：%v", err)
  6. 	}
  7. 	buf.Write(data)
  8. }
  10. if err := ioutil.WriteFile("test.bson", buf.Bytes(), 0644); err != nil {
  11. 	fmt.Printf("无法写入BSON文件：%v", err)
  12. }

运行bsondump --pretty test.bson，输出将会是：

  1. {
  2.         "_id": "abc",
  3.         "text": "def"
  4. }
  5. {
  6.         "_id": "uvw",
  7.         "text": "xyz"
  8. }
  9. 2022-02-09T10:23:44.886+0100    找到2个对象

请注意，如果直接写入文件，则不需要使用缓冲区：

  1. f, err := os.Create("test.bson")
  2. if err != nil {
  3. 	log.Panicf("os.Create失败：%v", err)
  4. }
  5. defer f.Close()
  7. for _, item := range items {
  8. 	data, err := bson.Marshal(item)
  9. 	if err != nil {
  10. 		log.Panicf("bson.Marshal失败：%v", err)
  11. 	}
  12. 	if _, err := f.Write(data); err != nil {
  13. 		log.Panicf("f.Write失败：%v", err)
  14. 	}
  15. }
英文:

You want independent BSON documents, so marshal the items individually:

  1. buf := &bytes.Buffer{}
  2. for _, item := range items {
  3. 	data, err := bson.Marshal(item)
  4. 	if err != nil {
  5. 		fmt.Printf("Failed to marshal BSON item: '%v'", err)
  6. 	}
  7. 	buf.Write(data)
  8. }
  10. if err := ioutil.WriteFile("test.bson", buf.Bytes(), 0644); err != nil {
  11. 	fmt.Printf("Failed to write BSON file: '%v'", err)
  12. }

Running bsondump --pretty test.bson, the output will be:

  1. {
  2.         "_id": "abc",
  3.         "text": "def"
  4. }
  5. {
  6.         "_id": "uvw",
  7.         "text": "xyz"
  8. }
  9. 2022-02-09T10:23:44.886+0100    2 objects found

Note that the buffer is not needed if you write directly to the file:

  1. f, err := os.Create("test.bson")
  2. if err != nil {
  3. 	log.Panicf("os.Create failed: %v", err)
  4. }
  5. defer f.Close()
  7. for _, item := range items {
  8. 	data, err := bson.Marshal(item)
  9. 	if err != nil {
  10. 		log.Panicf("bson.Marshal failed: %v", err)
  11. 	}
  12. 	if _, err := f.Write(data); err != nil {
  13. 		log.Panicf("f.Write failed: %v", err)
  14. 	}
  15. }

huangapple
  • 本文由 发表于 2022年2月9日 17:16:10
  • 转载请务必保留本文链接：https://go.coder-hub.com/71046804.html
  • bson
  • go
  • marshalling
  • mongodb
  • mongoimport
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