在MongoCollection< Document>中找到 [英] find in MongoCollection<Document>

问题描述

我有一个 MongoCollection< Document> ，我在其中分配了一个集合。
我正在尝试通过他的ID找到用户。

I have a MongoCollection<Document> in which I assign a collection. I'm trying to find a user by his id.

user = (Document) usersCollection.find(new Document("_id", username));

我收到错误

java.lang.ClassCastException：com.mongodb.FindIterableImpl不能
强制转换为org.bson.Document

java.lang.ClassCastException: com.mongodb.FindIterableImpl cannot be cast to org.bson.Document

当我尝试

    BasicDBObject query = new BasicDBObject(); 
    BasicDBObject fields = new BasicDBObject("_id", username);
    usersCollection.find(query, fields);

我收到错误

MongoCollection类型中的方法find（Bson，Class）不适用于参数（BasicDBObject，BasicDBObject）

The method find(Bson, Class) in the type MongoCollection is not applicable for the arguments (BasicDBObject, BasicDBObject)

推荐答案

尝试创建一个过滤器以传递给 find（） 方法获取集合中的文档子集。例如，要查找 _id 字段的值为 test 的文档，您将执行以下操作：

Try to create a filter to pass to the find() method to get a subset of the documents in your collection. For example, to find the document for which the value of the _id field is test, you would do the following:

import static com.mongodb.client.model.Filters.*;

MongoClient client = new MongoClient();
MongoDatabase database = client.getDatabase("mydb");
MongoCollection<Document> collection = database.getCollection("mycoll");
myDoc = collection.find(eq("_id", "test")).first();
System.out.println(myDoc.toJson());

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