Golang: MongoDB – 在投影中计算嵌套数组的长度

huangapple
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英文:

Golang: MongoDB - count length of nested arrays in Projection

问题

在MongoDB中，我喜欢将所有嵌套数组的长度加在一起进行计数。
这只是一个MongoDB文档。

  1. idForDB := "621101966rf42c24a8f41b87"
  2. ctx, cancel := context.WithTimeout(context.Background(), time.Second * 20)
  3. defer cancel()
  4. options := options.FindOneOptions{
  5.         Projection: bson.M{
  6.             "test":          "$test",
  7.             "count": bson.M{}, // count应该放在这里
  8.         },
  9.     }
  10. result := clients.MongoClient.Database("somedb").Collection("somecollection").FindOne(ctx, bson.M{"_id": idForDB}, &options)

所有在"number"下的对象都要被计数

  1. {
  2.    "test":"other",
  3.    "list":[
  4.       {
  5.         "number":[
  6.             {
  7.                 "value": "1"
  8.             }, 
  9.             {
  10.                 "value": "2"
  11.             },
  12.             {
  13.                 "value": "2"
  14.             }
  15.         ]
  16.       },
  17.       {
  18.         "number":[
  19.             {
  20.                 "value": "1"
  21.             }, 
  22.             {
  23.                 "value": "2"
  24.             },
  25.             {
  26.                 "value": "2"
  27.             }
  28.         ]
  29.       },
  30.       {
  31.         "number":[
  32.             {
  33.                 "value": "1"
  34.             }, 
  35.             {
  36.                 "value": "2"
  37.             }
  38.         ]
  39.       }
  40.    ]
  41. }

"Number"字段的输出应该是8，因为在"number"对象下有8个文档。

英文:

In MongoDB i like to count all length of nested arrays togehter.
It is just one mongoDB document.

  1. idForDB := "621101966rf42c24a8f41b87"
  2. ctx, cancel := context.WithTimeout(context.Background(), time.Second * 20)
  3. defer cancel()
  4. options := options.FindOneOptions{
  5.         Projection: bson.M{
  6.             "test":          "$test",
  7.             "count": bson.M{}, // count should placed here
  8.         },
  9.     }
  10. result := clients.MongoClient.Database("somedb").Collection("somecollection").FindOne(ctx, bson.M{"_id": idForDB}, &options)

All objects under number are to be counted

  1. {
  2.    "test":"other",
  3.    "list":[
  4.       {
  5. 		"number":[
  6. 			{
  7. 				"value": "1"
  8. 			}, 
  9. 			{
  10. 				"value": "2"
  11. 			},
  12. 			{
  13. 				"value": "2"
  14. 			}
  15. 		]
  16.       },
  17.       {
  18. 		"number":[
  19. 			{
  20. 				"value": "1"
  21. 			}, 
  22. 			{
  23. 				"value": "2"
  24. 			},
  25. 			{
  26. 				"value": "2"
  27. 			}
  28. 		]
  29.       },
  30.       {
  31. 		"number":[
  32. 			{
  33. 				"value": "1"
  34. 			}, 
  35. 			{
  36. 				"value": "2"
  37. 			}
  38. 		]
  39.       }
  40.    ]
  41. }

The output for the "Number" field should be 8 because there are 8 documents under the "number" object.

答案1

得分: 1

使用MongoDB语法，你可以使用$reduce来实现：

  1. db.collection.aggregate([
  2.   {$project: {
  3.       test: "$test",
  4.       count: {
  5.         $reduce: {
  6.           input: "$list",
  7.           initialValue: 0,
  8.           in: {$add: ["$$value", {$size: "$$this.number"}]}
  9.         }
  10.       }
  11.     }
  12.   }
  13. ])

在playground example上查看它的工作原理。

英文:

Using mongoDB syntax, you can use $reduce for it:

  1. db.collection.aggregate([
  2.   {$project: {
  3.       test: "$test",
  4.       count: {
  5.         $reduce: {
  6.           input: "$list",
  7.           initialValue: 0,
  8.           in: {$add: ["$$value", {$size: "$$this.number"}]}
  9.         }
  10.       }
  11.     }
  12.   }
  13. ])

See how it works on the playground example

huangapple
  • 本文由 发表于 2022年7月11日 22:21:05
  • 转载请务必保留本文链接：https://go.coder-hub.com/72940060.html
  • go
  • mongodb
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