如何在Java中从mongodb集合返回数据

Question

我有一个MongoDB数据库，其中有一个集合，如下所示：

+----------+-------------+
| Field    | Type        |
+----------+-------------+
| sha      | varchar(40) |
| filename | text        | 
+----------+-------------+

我还有一个MySQL数据库，其中有一个表，如下所示：

+----------+-------------+
| Field    | Type        |
+----------+-------------+
| sha      | varchar(40) |
| filename | text        | 
+----------+-------------+

MySQL表中的SHA列包含50000条记录，而filename列为空，这是我希望从上面的MongoDB集合中获得的。我想将此表中的SHA键与MongoDB集合中的SHA键进行比较。规则需要是，如果SHA存在于Mongo集合中，则拉取与该SHA密钥相对应的文件名，并将其插入到本地MySQL中与该SHA密钥相对应的文件名字段中。

如何根据MySQL中的sha值返回filename值？我只是不熟悉MongoDB查询是如何工作的，我的Mongodb查询正确吗？

我当前编写的代码如下所示：

//Get sha values from mysql and compare with the sha values in mongo and return corresponding filenames
Statement sqlStmt = mysqlConn.createStatement();
HashMap < String, String > shaFileNameMap = new HashMap < String, String > ();

//get sha values from local mysql
String shaQuery = "select * from commit_files";
ResultSet results = sqlStmt.executeQuery(shaQuery);
String sha = null;
String filename = null;

//Store returned sha values in a hashmap
while (results.next()) {
  sha = results.getString("sha");
  filename = results.getString("filename");
  //Store in a map
  shaFileNameMap.put(sha, filename);
}

for (Map.Entry < String, String > entry: shaFileNameMap.entrySet()) {
  String key = entry.getKey();

  //get all filenames matching the list from mongo db and insert into mysql
  DBCollection commits = db.getCollection("commits");
  DBObject query = new BasicDBObject();
  BasicDBObject fields = new BasicDBObject("sha", "" + key + "");
  DBCursor curs = commits.find(query, fields);
  while (curs.hasNext()) {
    DBObject o = curs.next();

    //The code to insert filenames into Mysql goes here
  }
}

Answer 1

我的建议是:使用当前的API：

...
MongoClient client = new MongoClient();
MongoCollection<Document> coll = client .getDatabase("xyz").getCollection("myColl");
...
// in the query loop:
FindIterable<Document> res = coll.find(Filters.eq("sha", key);
// and go through the find iterable which has 0 to many entries

关键的一点是，com.mongodb.client.model.Filters类将您需要的所有内容都作为创建查询的快捷方式。

https://api.mongodb.com/java/current/com/mongodb/client/model/Filters.html上的API-doc