获取MongoDB Java中数组子文档字段的值。

huangapple
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英文:

Retrieve only the value of an arrays sub-document field using MongoDB Java

问题

我有一个数据库：

{
"_id": {
"$oid": "1"
},
"lastName": {
"lastName": "James"
},
"data": [{
"day": "20-09-2020 11:35:02",
"hoursWorked": "0小时：5分钟：321秒"
}, {
"day": "20-09-2020 11:35:29",
"hoursWorked": "0小时：5分钟：321秒"
}]
}

如何仅检索“data”字段的子字段“hoursWorked”的值。
因此，我只需要该字段的值或所有这些值，即0小时：5分钟：321秒。

我使用以下代码；然而，我仍然无法检索到该值。

  1. Document document = collection
  2.     .find(new BasicDBObject("_id", y))
  3.     .projection(Projections.fields(Projections.include("data.hoursWorked"), excludeId())).first();
  4. System.out.println(document);
  5. }
英文:

I have a database:

  1. {
  2. "_id": {
  3.     "$oid": "1"
  4. },
  5. "lastName": {
  6.     "lastName": "James"
  7. },
  8. "data": [{
  9.     "day": "20-09-2020 11:35:02",
  10.     "hoursWorked": "0 hours : 5 mins : 321 secs"
  11. }, {
  12.     "day": "20-09-2020 11:35:29",
  13.     "hoursWorked": "0 hours : 5 mins : 321 secs"
  14. }]
  15. }

How do I retrieve only the value of subfield "hoursWorked" of "data" field.
So, I need only the value or all values of such field, 0 hours : 5 mins : 321 secs.

I use the following; however, I still cannot retrieve the value.

  1. Document document = collection
  2.                 .find(new BasicDBObject("_id", y))
  3.                 .projection(Projections.fields(Projections.include("data.hoursWorked"), excludeId())).first();
  4.         System.out.println(document);
  5.         }

答案1

得分: 1

  1. 使用 MongoDB Java 驱动程序：
  3. List<Bson> pipeline = 
  4.     Arrays.asList(
  5.         project(
  6.              fields(
  7.                  excludeId(), 
  8.                  computed("hoursWorked", 
  9.                       eq("$reduce", 
  10.                           and(eq("input", "$data"), eq("initialValue", Arrays.asList()),
  11.                               eq("in", eq("$concatArrays", Arrays.asList("$$value", Arrays.asList("$$this.hoursWorked")))) 
  12.                           ) 
  13.                       ) 
  14.                   )
  15.               )
  16.           ),
  17.          unwind("$hoursWorked")
  18.     );
  19.     
  20. collection.aggregate(pipeline)
  21.              .into(new ArrayList<Document>())
  22.              .forEach(doc -> System.out.println(doc.get("hoursWorked")));
  24. 打印data数组中的两个值：
  26. 0小时：5分钟：321秒
  27. 0小时：5分钟：322秒
英文:

Using MongoDB Java Driver:

  1. List&lt;Bson&gt; pipeline = 
  2.     Arrays.asList(
  3.         project(
  4.              fields(
  5.                  excludeId(), 
  6.                  computed(&quot;hoursWorked&quot;, 
  7.                       eq(&quot;$reduce&quot;, 
  8.                           and(eq(&quot;input&quot;, &quot;$data&quot;), eq(&quot;initialValue&quot;, Arrays.asList()),
  9.                               eq(&quot;in&quot;, eq(&quot;$concatArrays&quot;, Arrays.asList(&quot;$$value&quot;, Arrays.asList(&quot;$$this.hoursWorked&quot;) ) ) ) 
  10.                           ) 
  11.                       ) 
  12.                   ) 
  13.               )
  14.           ),
  15.          unwind(&quot;$hoursWorked&quot;)
  16.     );
  18. collection.aggregate(pipeline)
  19.              .into(new ArrayList&lt;Document&gt;())
  20.              .forEach(doc -&gt; System.out.println(doc.get(&quot;hoursWorked&quot;)));

Prints two values from the data array:

  1. 0 hours : 5 mins : 321 secs
  2. 0 hours : 5 mins : 322 secs

答案2

得分: 0

你可以使用投影 $project。

  1. db.collection.aggregate([
  2.   {
  3.     $project: {
  4.       "data.hoursWorked": 1
  5.     }
  6.   }
  7. ])

在 Mongo 游乐场 中运行

在 Spring Boot 中，你需要自动装配 mongoTemplate：

  1. @Autowired
  2. MongoTemplate mongoTemplate;

聚合代码：

  1. public List<Object> test(){
  2.     Aggregation aggregation = Aggregation.newAggregation(
  3.         a-> new Document("$project",
  4.                 new Document("data.hoursWorked", 1)
  5.         )
  6.     ).withOptions(AggregationOptions.builder().allowDiskUse(Boolean.TRUE).build());
  8.     return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(YOUR_COLLECTION.class), Object.class).getMappedResults();
  9. }

更新 1

使用 Bson.Document：

  1. Document nodes = (Document) collection
  2.         .find(new BasicDBObject("_id", "1"))
  3.         .projection(Projections.fields(Projections.include("data.hoursWorked"), Projections.excludeId()))
  4.         .first();
  6. List<Document> list = (List<Document>) nodes.get("data");
  7. for(Document d:list){
  8.     System.out.println(d.get("hoursWorked"));
  9. }
英文:

You can use projection $project.

  1. db.collection.aggregate([
  2.   {
  3.     $project: {
  4.       &quot;data.hoursWorked&quot;: 1
  5.     }
  6.   }
  7. ])

Working Mongo playground

In spring boot, you need to autowire the mongoTemplate

  1. @Autowired
  2. MongoTemplate mongoTemplate;

The aggregation code,

  1. public List&lt;Object&gt; test(){
  2. 	Aggregation aggregation = Aggregation.newAggregation(
  3. 		a-&gt; new Document(&quot;$project&quot;,
  4. 				new Document(&quot;data.hoursWorked&quot;,1)
  5. 		)
  7. 	).withOptions(AggregationOptions.builder().allowDiskUse(Boolean.TRUE).build());
  9. 	return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(YOUR_COLLECTION.class), Object.class).getMappedResults();
  10. }

Update 1

Using Bson.Doument

  1. Document nodes = (Document) collection
  2. 				.find(new BasicDBObject(&quot;_id&quot;, &quot;1&quot;))
  3. 				.projection(Projections.fields(Projections.include(&quot;data.hoursWorked&quot;), Projections.excludeId()))
  4. 				.first();
  6. 		List&lt;Document&gt; list = (List&lt;Document&gt;) nodes.get(&quot;data&quot;);
  7. 		for(Document d:list){
  8. 			System.out.println(d.get(&quot;hoursWorked&quot;));
  9. 		}

huangapple
  • 本文由 发表于 2020年9月21日 07:41:12
  • 转载请务必保留本文链接：https://go.coder-hub.com/63984636.html
  • java
  • mongodb
  • mongodb-java
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