After successful insertion, the following is displayed

This completes nesting of documents, that is, representing an association between two documents.

Using the JDK

The JDK is used here to connect. First add dependencies

< the dependency > < groupId > org. Mongo < / groupId > < artifactId > mongo - driver < / artifactId > < version > 3.5.0 < / version > </dependency>Copy the code

To connect

MongoClient = new MongoClient(MongoClient = new MongoClient)"106.53.115.12", 27017); MongoDatabase = mongoclient.getDatabase ("koa");  
       System.out.println("Connect to database successfully");
        
      }catch(Exception e){
        System.err.println( e.getClass().getName() + ":" + e.getMessage() );
     }
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To insert

List<Document> collections = new ArrayList<Document>();
Document d1 = new Document();
d1.append("name".Romance of The Three Kingdoms).append("author"."Luo Guanzhong");
Document d2 = new Document();
d2.append("name".A Dream of Red Mansions).append("author", d1);
collections.add(d2);
c.insertMany(collections);
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The query data is as follows

{
	"name" : A Dream of Red Mansions."author": {
		"name": Romance of The Three Kingdoms."author": "Luo Guanzhong"}}Copy the code

At this point, the nesting of documents is complete

Foreign key query

Use JS language, query association

Use new DBRef for foreign key query. The following fields are now available for DBRef.

$ref

         该$refThe field contains the name of the collection in which the reference document is located.$id

        该$idThe field contains the _id reference to the value of the field in the document.$dbOptional. Contains the name of the database in which the reference document resides. Only some drivers support it$dbReference, the field description can be associated across collectionsCopy the code

Here the collection operations are associated as follows

Var a={value:"1"}  
 
> var b={value:"2"}  
 
> var c={value:"9"}  
 
> var d={value:"10"} > db. A.s ave > db (a). The A.s ave (b) > db. A.s ave (c) > db. A.s ave (d) / / collection data query > db. A.find()                                                                                                 
 
{ "_id" : ObjectId("4e3f33ab6266b5845052c02b"), "value" : "1" }  
 
{ "_id" : ObjectId("4e3f33de6266b5845052c02c"), "value" : "2" }  
 
{ "_id" : ObjectId("4e3f33e06266b5845052c02d"), "value" : "9" }  
 
{ "_id" : ObjectId("4e3f33e26266b5845052c02e"), "value" : "10" }  
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To carry out the association of sets, the new DBRef method is used to complete the association of sets

In this case, new DBRef is used as the keyword. A is key and ObjectId is value. > var Ba={Apid:[new DBRef('A',ObjectId("4e3f33de6266b5845052c02c")), value: 3} / collection/save > db. B.s ave (Ba) > var Ba = {Apid: [new DBRef ('A',ObjectId("4e3f33de6266b5845052c02c"))],value:4}  
 
> db.B.insert(Ba)                                                              
 
> var Ba={Apid:[new DBRef('A',ObjectId("4e3f33de6266b5845052c02c"))],value:7}  
 
> db.B.insert(Ba)                                                              
 
> var Ba={Apid:[new DBRef('A',ObjectId("4e3f33de6266b5845052c02c")), value: 8} > db. B.i nsert (Ba) / / query > db. B. ind () / / as you can see, has successfully associated {"_id" : ObjectId("4e3f3dd96266b5845052c035"), "Apid": [{"$ref" : "A"."$id" : ObjectId("4e3f33de6266b5845052c02c")},"value": 3} {"_id" : ObjectId("4e3f3de16266b5845052c036"), "Apid": [{"$ref" : "A"."$id" : ObjectId("4e3f33de6266b5845052c02c")},"value": 4} {"_id" : ObjectId("4e3f3dec6266b5845052c037"), "Apid": [{"$ref" : "A"."$id" : ObjectId("4e3f33de6266b5845052c02c")},"value": 7} {"_id" : ObjectId("4e3f3df06266b5845052c038"), "Apid": [{"$ref" : "A"."$id" : ObjectId("4e3f33de6266b5845052c02c")},"value"8} :Copy the code

Use mongo-Java

DBRef refB = new DBRef(db,"transations", obj.get("_id")); // Create a new set DBObject subObj = new BasicDBObject(); // Insert subobj. put("brand", refB); // Save accounts. Save (subObj);Copy the code

The query result is as follows

The public,