MongoDB的樹找到後裔的Java

Question

我有一個這樣的樹蒙戈：

> db.data.find() 
{ "_id" : "07c", "path" : null } 
{ "_id" : "a", "path" : "07c,a" } 
{ "_id" : "b", "data" : "{\"c\":\"olaC\",\"d\":\"olaD\"}", "path" : "07c,a,b" } 
{ "_id" : "c", "c" : "{\"c\":\"olaC\",\"d\":\"olaD\"}", "path" : "07c,a,b,c" } 
{ "_id" : "d", "d" : "{\"d\":\"olaD\"}", "data" : "{\"c\":\"olaC\",\"d\":\"olaD\"}", "path" : "07c,a,b,c,d" } 

我想檢索B的所有後代。

如果我這樣做是MongoDB的控制檯，我得到的後代精：

> db.data.find({ path: /,b,/ }) 
{ "_id" : "c", "c" : "{\"c\":\"olaC\",\"d\":\"olaD\"}", "path" : "07c,a,b,c" } 
{ "_id" : "d", "d" : "{\"d\":\"olaD\"}", "data" : "{\"c\":\"olaC\",\"d\":\"olaD\"}",  "path" : "07c,a,b,c,d" } 

，但如果我這樣做在Java中：

BasicDBObject query = new BasicDBObject(); 
query.put("path", "/,"+array[i]+",/"); 
DBCursor cursor = coll.find(query); 
while(cursor.hasNext()){ 
    System.out.println(cursor.next().toString()); 
} 

從調試器查詢中包含這樣的：{ 「path」：「/，b，/」}

我根本沒有後代...爲什麼這不起作用？

http://docs.mongodb.org/manual/tutorial/model-tree-structures-with-materialized-paths/

Answer 1

/../是MongoDB的shell特殊。它不是簡單的包含正則表達式的字符串，而是由shell解析並用作正則表達式的東西。

從Java做到這一點，你會做這樣的事情：

BasicDBObject query = new BasicDBObject(); 
query.put("name", Pattern.compile(","+array[i]+",")); 
DBCursor cursor = coll.find(query); 
while(cursor.hasNext()){ 
    System.out.println(cursor.next().toString()); 
} 

參見：How to query mongodb with 「like」 using the java api?