[ MongoDB 教學 ] Java MongoDB : Update document

來源自 這裡 
前言 : 
在 MongoDB 的 API 裡, 你可以使用 collection.update() 來更新一個已經存在的 document. 底下的 Tutorial 就透過一些 user cases 來說明如何對 MongoDB 進行 update document. 
Note : 

Before proceed on this tutorial, you should understand how-to-do, update in mongoDB, list of supported update modifiers, and the Java DBCollection update()method.

在下面的範例, collection 中已經有以下 documents : 

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1. {  
2.     "hosting" : "hostA",  
3.     "type" : "vps",  
4.     "clients" : 1000  
5. },  
6. {  
7.     "hosting" : "hostB",  
8.     "type" : "dedicated server",  
9.     "clients" : 100  
10. },  
11. {  
12.     "hosting" : "hostC",  
13.     "type" : "vps",  
14.     "clients" : 900  
15. }  

DBCollection.update() examples : 
底下有 4 個 user case 對 collection 更新的範例. 範例中因為涉及對 collection 進行搜尋並更新, 固並不保證現有 collection 中的文件一定會被更新. 

- Example 1 
找出 hosting = hostB, 並用新的 document 來 update 它 : 

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1. BasicDBObject newDocument = new BasicDBObject();  
2. newDocument.put("hosting", "hostB");  
3. newDocument.put("type", "shared host");  
4. newDocument.put("clients", 111);  
5.   
6. collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);  

執行結果如下 : 

{ "_id" : { "$oid" : "4fc6d170c28ffdebd46236af"} , "hosting" : "hostA" , "type" : "vps" , "clients" : 1000}
{ "_id" : { "$oid" : "4fc6d170c28ffdebd46236b0"} , "hosting" : "hostB" , "type" : "shared host" , "clients" : 111}
{ "_id" : { "$oid" : "4fc6d170c28ffdebd46236b1"} , "hosting" : "hostB" , "type" : "vps" , "clients" : 900}

- Example 2 
這個範例使用了 "$inc" 的 modifier 來 increase 某個特定 field 的值 : Find hosting = hostB, update the "clients" value by increasing its value from 100 to 199, (100 + 99) = 199 : 

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1. BasicDBObject newDocument = new BasicDBObject().append("$inc", new BasicDBObject().append("clients", 99));  
2.   
3. collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);  

執行結果如下 : 

{ "_id" : { "$oid" : "4fc6d6a4c28f951ffeba5e1d"} , "hosting" : "hostA" , "type" : "vps" , "clients" : 1000}
{ "_id" : { "$oid" : "4fc6d6a4c28f951ffeba5e1e"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 199}
{ "_id" : { "$oid" : "4fc6d6a4c28f951ffeba5e1f"} , "hosting" : "hostB" , "type" : "vps" , "clients" : 900}

- Example 3 
這個範例使用 "$set" modifier 來更新特定 field 的值, 所以你就不用提供完整的 document : Find hosting = hostA, update the "type" from "vps" to "dedicated server" : 

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1. BasicDBObject newDocument3 = new BasicDBObject().append("$set", new BasicDBObject().append("type", "dedicated server"));  
2.   
3. collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);  

執行結果如下 : 

{ "_id" : { "$oid" : "4fc6d82bc28fe581466794f9"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{ "_id" : { "$oid" : "4fc6d82bc28fe581466794fa"} , "hosting" : "hostB" , "type" : "vps" , "clients" : 900}
{ "_id" : { "$oid" : "4fc6d82bc28fe581466794f8"} , "clients" : 1000 , "hosting" : "hostA" , "type" : "dedicated server"}

Note : Why need to use $set? 

By default, if you update a document like this :

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1. BasicDBObject newDocument3 = new BasicDBObject().append("type", "dedicated server");  
2.   
3. collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);  

It will replaced the entire old document, see following result :

{"_id":{ "$oid" : "x"} , "type" : "dedicated server"}
{"_id":{ "$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id":{ "$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}

With “$set” modifier, only particular value is updated.

- Example 4 
這個範例設定 "multi" 參數讓你可以同時 update 多個 matched query 的 documents. 使用方法為 update(DBObject q, DBObject o, boolean upsert, boolean multi) : Find type = "vps", update all the matched documents, "clients" value to 888 : 

* upsert - if the database should create the element if it does not exist
* multi - if the update should be applied to all objects matching

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1. //find type = vps , update all matched documents , "clients" value to 888  
2. BasicDBObject updateQuery = new BasicDBObject().append("$set",  new BasicDBObject().append("clients", "888"));  
3.   
4. //both methods are doing the same thing.  
5. //collection.updateMulti(new BasicDBObject().append("type", "vps"), updateQuery);  
6. collection.update(new BasicDBObject().append("type", "vps"), updateQuery, false, true);  

執行結果如下 : 

{ "_id" : { "$oid" : "4fc6dafbc28f926c06f04c6f"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{ "_id" : { "$oid" : "4fc6dafbc28f926c06f04c6e"} , "clients" : "888" , "hosting" : "hostA" , "type" : "vps"}
{ "_id" : { "$oid" : "4fc6dafbc28f926c06f04c70"} , "clients" : "888" , "hosting" : "hostB" , "type" : "vps"}

Note : Why need to use “multi”? 

If you update a document without the “multi” parameter like this :

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1. BasicDBObject updateQuery = new BasicDBObject().append("$set", new BasicDBObject().append("total clients", "888"));  
2.   
3.        //multi default to false  
4. collection.update(new BasicDBObject().append("type", "vps"), updateQuery);  

You will noticed that only the first matched document is updated.

{"_id":{ "$oid" : "x"} , "hosting" : "hostA" , "clients" : "888" , "type" : "vps"}
{"_id":{ "$oid" : "x"} , "hosting" : "hostB" , "type" : "dedicated server" , "clients" : 100}
{"_id":{ "$oid" : "x"} , "hosting" : "hostC" , "type" : "vps" , "clients" : 900}

To update a set of matched documents, you need to set “multi” to true.

完整代碼 : 
底下是上述 4 個範例代碼的完整版 : 

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1. package ir.stat.test.mongodb;  
2.   
3. import com.mongodb.BasicDBObject;  
4. import com.mongodb.DB;  
5. import com.mongodb.DBCollection;  
6. import com.mongodb.DBCursor;  
7. import com.mongodb.Mongo;  
8.   
9. public class UpdateEx {  
10.     public static String MangoDB_IP = "192.168.80.168";  
11.     public static String DB_NAME = "test";  
12.     public static Mongo m = null;  
13.   
14.     public static void dropCollection(String name) throws Exception  
15.     {  
16.         if(m==null) m = new Mongo(MangoDB_IP);  
17.         DB db = m.getDB(DB_NAME);  
18.         DBCollection coll = db.getCollection(name);  
19.         coll.drop();  
20.     }  
21.       
22.     public static DBCollection retvCollection(String name) throws Exception {  
23.         if(m==null) m = new Mongo(MangoDB_IP);  
24.         DB db = m.getDB(DB_NAME);  
25.   
26.         DBCollection coll = db.getCollection(name);  
27.         return coll;  
28.     }  
29.       
30.     public static void insert(DBCollection coll, String hosting, String type, int clients)  
31.     {  
32.         BasicDBObject doc = new BasicDBObject();  
33.         doc.put("hosting", hosting);  
34.         doc.put("type", type);  
35.         doc.put("clients", clients);  
36.         coll.insert(doc);  
37.     }  
38.       
39.     public static void showCollection(DBCollection coll)  
40.     {  
41.         DBCursor cursorDocJSON = coll.find();  
42.         while (cursorDocJSON.hasNext()) {  
43.             System.out.println(cursorDocJSON.next());  
44.         }  
45.     }  
46.       
47.     // A normal way to update an existing document. Find hosting = hostB, and update it with a new document.  
48.     public static void exam01(DBCollection collection) throws Exception  
49.     {  
50.         BasicDBObject newDocument = new BasicDBObject();  
51.         newDocument.put("hosting", "hostB");  
52.         newDocument.put("type", "shared host");  
53.         newDocument.put("clients", 111);  
54.        
55.         collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);  
56.     }     
57.       
58.     // Find hosting = hostB, update the "clients" value by increasing its value  
59.     public static void exam02(DBCollection collection) throws Exception  
60.     {  
61.         BasicDBObject newDocument = new BasicDBObject().append("$inc", new BasicDBObject().append("clients", 99));  
62.   
63.         collection.update(new BasicDBObject().append("hosting", "hostB"), newDocument);  
64.     }  
65.       
66.     // Find hosting = hostA, update the “type” from “vps” to “dedicated server”.  
67.     public static void exam03(DBCollection collection) throws Exception  
68.     {  
69.         BasicDBObject newDocument3 = new BasicDBObject().append("$set", new BasicDBObject().append("type", "dedicated server"));  
70.            
71.         collection.update(new BasicDBObject().append("hosting", "hostA"), newDocument3);  
72.     }  
73.       
74.     public static void exam04(DBCollection collection) throws Exception  
75.     {  
76.         //find type = vps , update all matched documents , "clients" value to 888  
77.         BasicDBObject updateQuery = new BasicDBObject().append("$set",  new BasicDBObject().append("clients", "888"));  
78.        
79.         //both methods are doing the same thing.  
80.         //collection.updateMulti(new BasicDBObject().append("type", "vps"), updateQuery);  
81.         collection.update(new BasicDBObject().append("type", "vps"), updateQuery, false, true);  
82.     }  
83.       
84.     public static void main(String args[]) throws Exception  
85.     {  
86.         dropCollection("tutorial_update");  // Reset collection "tutorial_update"  
87.         DBCollection coll = retvCollection("tutorial_update");        
88.         insert(coll,"hostA" ,"vps" ,1000);  
89.         insert(coll,"hostB" ,"dedicated server" ,100);  
90.         insert(coll,"hostB" ,"vps" ,900);  
91.           
92.         exam04(coll); showCollection(coll);  
93.     }  
94. }