使用MongoDb创建索引 [英] Create an index with MongoDb
问题描述
我是MongoDB的初学者,我正在尝试一些东西。
我想存储URL并避免重复的URL我在url上创建了一个唯一的索引。
喜欢它
I'm beginner with MongoDB and i'm trying some stuff. I want to store URL and to avoid duplicate URL I create an unique index on the url. Like that
collection.createIndex(new BasicDBObject("url", type).append("unique", true));
但是每次启动我的程序时,索引都会重新创建不是吗?
But each time I launch my program the index is create again isn't it ?
因为,现在我的程序只插入一个网址http://site.com,如果我重新启动我的程序,这个网址会再次插入,就像没有索引一样。
Because, now my program is only inserting one url "http://site.com" and if I restart my program this url is insert again like if there isn't index.
每次创建索引是处理索引的错误方法吗?
Creating the index each time is the wrong way to handle an index ?
以下是我的代码示例
mongo.getCollection().ensureIndex(new BasicDBObject("url", 1).append("unique", "true"));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
输出:
{ "_id" : { "$oid" : "50d627cf44ae5d6b5e9cf106"} , "url" : "http://site.com" , "crawled" : 0}
{ "_id" : { "$oid" : "50d627cf44ae5d6b5e9cf107"} , "url" : "http://site.com" , "crawled" : 0}
谢谢
编辑:
这是我的班级Mongo处理MongoDB
导入java.net.UnknownHostException;
import java.util.List;
import java.util.Set;
Here is my class Mongo which handle MongoDB import java.net.UnknownHostException; import java.util.List; import java.util.Set;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.BasicDBObject; import com.mongodb.DB; import com.mongodb.DBCollection; import com.mongodb.DBObject; import com.mongodb.MongoClient;
public class Mongo {
private MongoClient mongoClient;
private DB db;
private DBCollection collection;
private String db_name;
public Mongo(String db){
try {
mongoClient = new MongoClient( "localhost" , 27017 );
this.db = mongoClient.getDB(db);
this.db_name = db;
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
public void drop(){
mongoClient.dropDatabase(db_name);
}
public void listCollections(){
Set<String> colls = db.getCollectionNames();
for (String s : colls) {
System.out.println(s);
}
}
public void listIndex(){
List<DBObject> list = collection.getIndexInfo();
for (DBObject o : list) {
System.out.println("\t" + o);
}
}
public void setCollection(String col){
this.collection = db.getCollection(col);
}
public void insert(BasicDBObject doc){
this.collection.insert(doc);
}
public DBCollection getCollection(){
return collection;
}
public void createIndex(String on, int type){
collection.ensureIndex(new BasicDBObject(on, type).append("unique", true));
}
}
这里是我的班级处理我的程序
And here is my class which handle my program
public class Explorer {
private final static boolean DEBUG = false;
private final static boolean RESET = false;
private Mongo mongo;
private String host;
public Explorer(String url){
mongo = new Mongo("explorer");
mongo.setCollection("page");
if (RESET){
mongo.drop();
System.out.println("Set RESET to FALSE and restart the program.");
System.exit(1);
}
if (DEBUG) {
mongo.listCollections();
}
this.host = url.toLowerCase();
BasicDBObject doc = new BasicDBObject("url", "http://site.com").append("crawled", 0);
mongo.getCollection().ensureIndex(new BasicDBObject("url", 1).append("unique", true));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
mongo.getCollection().insert(new BasicDBObject("url", "http://site.com").append("crawled", 0));
process();
}
private void process(){
BasicDBObject query = new BasicDBObject("crawled", 0);
DBCursor cursor = mongo.getCollection().find(query);
try {
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
} finally {
cursor.close();
}
}
}
推荐答案
您需要将唯一值作为布尔值true传递,而不是作为字符串传递,并且它是选项的第二个参数:
You'll need to pass the unique value as the boolean value true, not as a string, and it's the second parameter that are options:
...ensureIndex(new BasicDBObject("url", 1), new BasicDBObject("unique", true));
另外,我使用mongo解释器手动测试:
Also, I tested it manually using the mongo interpreter:
> db.createCollection("sa")
{ "ok" : 1 }
> db.sa.ensureIndex({"url":1},{unique:true})
> db.sa.insert({url:"http://www.example.com", crawled: true})
> db.sa.insert({url:"http://www.example.com", crawled: true})
E11000 duplicate key error index: test.sa.$url_1 dup key: { : "http://www.example.com" }
> db.sa.insert({url:"http://www.example2.com/", crawled: false})
> db.sa.insert({url:"http://www.example.com", crawled: false})
E11000 duplicate key error index: test.sa.$url_1 dup key: { : "http://www.example.com" }
>
只有两个对象:
> db.sa.find()
{ "_id" : ObjectId("50d636baa050939da1e4c53b"), "url" : "http://www.example.com", "crawled" : true }
{ "_id" : ObjectId("50d636dba050939da1e4c53d"), "url" : "http://www.example2.com/", "crawled" : false }
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