java - 使用来自java的自动增量字段在mongodb中插入文档

Question

我试图在一个事务中从 java 中插入一个带有序列号的文档。

类似的东西:

function getNextSequence(name) {
    var ret = db.counters.findAndModify(
        {
            query: { _id: name },
            update: { $inc: { seq: 1 } },
            new: true
        }
    );

    return ret.seq;
}
collection.insert({
    number: getNextSequence("userid"),
    name: "Some Name"
});

是否可以从 java 中执行此操作？最好使用官方 java 驱动程序。

Answer 1

遵循 creating an Auto-Incrementing Sequence Field 的文档，我们将其改编为在 Java 中与 Java MongoDB driver 一起使用.

示例实现:

import java.net.UnknownHostException;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;

public class TestAutoIncrement {

private final static String DB_NAME = "MyTestDB";
private final static String TEST_COLLECTION = "testCollection";
private final static String COUNTERS_COLLECTION = "countersCollection";

public static DBCollection testCollection;
public static DBCollection countersCollection;

public static void main(String[] args) {

    try {
        MongoClient mongoClient = new MongoClient();
        DB database = mongoClient.getDB(DB_NAME);
        testCollection = database.getCollection(TEST_COLLECTION);
        countersCollection = database.getCollection(COUNTERS_COLLECTION);
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }

    if (countersCollection.count() == 0) {
        createCountersCollection();
    }

    createTestCollection();
}

public static void createCountersCollection() {

    BasicDBObject document = new BasicDBObject();
    document.append("_id", "userid");
    document.append("seq", 0);
    countersCollection.insert(document);
}

public static Object getNextSequence(String name) {

    BasicDBObject searchQuery = new BasicDBObject("_id", name);
    BasicDBObject increase = new BasicDBObject("seq", 1);
    BasicDBObject updateQuery = new BasicDBObject("$inc", increase);
    DBObject result = countersCollection.findAndModify(searchQuery, null, null,
            false, updateQuery, true, false);

    return result.get("seq");
}

public static void createTestCollection() {

    BasicDBObject document = new BasicDBObject();
    document.append("_id", getNextSequence("userid"));
    document.append("name", "Sarah");
    testCollection.insert(document);

    document = new BasicDBObject();
    document.append("_id", getNextSequence("userid"));
    document.append("name", "Bob");
    testCollection.insert(document);

    document = new BasicDBObject();
    document.append("_id", getNextSequence("userid"));
    document.append("name", "Alex");
    testCollection.insert(document);
  }

}

必须特别注意findAndModify 方法。在 Java MongoDB 驱动程序 (2.12.4) 中，该方法具有 4 种不同的签名。
您必须使用一个可以让您传递 query 对象、update 对象和 returnNew boolean 值(必须设置为 true)。

那是因为，根据documentation :
默认情况下，返回的文档不包括对更新所做的修改。要返回包含更新修改的文​​档，请使用新选项。

我们需要返回包含更新修改的文​​档。