我有User
public class User {
private String name;
private String email;
public User () { }
public User(String name) {
this.name = name;
}
public User(String name, String email) {
this(name);
this.email = email;
}
// getters and setters
}
我也有简单的POJO Comment
public class Comment {
private String comment;
private Date date;
private String author;
public Comment() { }
public Comment(String comment, Date date, String author) {
this.comment = comment;
this.date = date;
this.author = author;
}
// getters and setters
}
我想如何将新用户插入集合中,并对此发表一些评论:
public static void main(String[] args) {
MongoClient client = new MongoClient();
MongoDatabase db = client.getDatabase("example");
MongoCollection<Document> collection = db.getCollection("object_arrays");
collection.drop();
List<Comment> reviews = new ArrayList<Comment>(){{
add(new Comment("cool guy", new Date(), "John Doe"));
add(new Comment("best joker", new Date(), "Vas Negas"));
add(new Comment("very stupid but very funny man", new Date(), "Bill Murphy"));
}};
Document user = new Document();
user.append("user", new User("0xFF", "email@email.com"))
.append("reviews", reviews)
.append("createDate", new Date());
collection.insertOne(user);
}
不幸的是,我有异常:
Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: Can't find a codec for class com.mongodb.course.com.mongodb.course.model.User.
at org.bson.codecs.configuration.CodecCache.getOrThrow(CodecCache.java:46)
at org.bson.codecs.configuration.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:63)
at org.bson.codecs.configuration.ChildCodecRegistry.get(ChildCodecRegistry.java:51)
at org.bson.codecs.DocumentCodec.writeValue(DocumentCodec.java:174)
at org.bson.codecs.DocumentCodec.writeMap(DocumentCodec.java:189)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:131)
at org.bson.codecs.DocumentCodec.encode(DocumentCodec.java:45)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:63)
at org.bson.codecs.BsonDocumentWrapperCodec.encode(BsonDocumentWrapperCodec.java:29)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:101)
at com.mongodb.connection.InsertCommandMessage.writeTheWrites(InsertCommandMessage.java:43)
at com.mongodb.connection.BaseWriteCommandMessage.encodeMessageBodyWithMetadata(BaseWriteCommandMessage.java:129)
at com.mongodb.connection.RequestMessage.encodeWithMetadata(RequestMessage.java:160)
at com.mongodb.connection.WriteCommandProtocol.sendMessage(WriteCommandProtocol.java:212)
at com.mongodb.connection.WriteCommandProtocol.execute(WriteCommandProtocol.java:101)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:67)
at com.mongodb.connection.InsertCommandProtocol.execute(InsertCommandProtocol.java:37)
at com.mongodb.connection.DefaultServer$DefaultServerProtocolExecutor.execute(DefaultServer.java:159)
at com.mongodb.connection.DefaultServerConnection.executeProtocol(DefaultServerConnection.java:286)
at com.mongodb.connection.DefaultServerConnection.insertCommand(DefaultServerConnection.java:115)
at com.mongodb.operation.MixedBulkWriteOperation$Run$2.executeWriteCommandProtocol(MixedBulkWriteOperation.java:455)
at com.mongodb.operation.MixedBulkWriteOperation$Run$RunExecutor.execute(MixedBulkWriteOperation.java:646)
at com.mongodb.operation.MixedBulkWriteOperation$Run.execute(MixedBulkWriteOperation.java:401)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:179)
at com.mongodb.operation.MixedBulkWriteOperation$1.call(MixedBulkWriteOperation.java:168)
at com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:230)
at com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:221)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:168)
at com.mongodb.operation.MixedBulkWriteOperation.execute(MixedBulkWriteOperation.java:74)
at com.mongodb.Mongo.execute(Mongo.java:781)
at com.mongodb.Mongo$2.execute(Mongo.java:764)
at com.mongodb.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:515)
at com.mongodb.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:306)
at com.mongodb.MongoCollectionImpl.insertOne(MongoCollectionImpl.java:297)
at com.mongodb.course.week3.ArrayListWithObject.main(ArrayListWithObject.java:34)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
我知道MongoDB的Java驱动程序无法将我的对象转换为Document
,并且它需要某种转换器。我也了解Codec
,CodecRegistry
和CodecProvider
接口。顺便说一句,是否有更简单的方法将对象转换为mongo文档?你能举例说明我该怎么办?
谢谢。
答案 0 :(得分:3)
您发布的代码的问题在于它默认不知道如何将您的pojo对象序列化为Json以将它们保存到数据库中。您可以使用MongoDB Java驱动程序执行此操作,但您需要做一些工作来序列化Comment ArrayList和User pojos。如果您添加一些杰克逊映射代码,您可以按如下方式执行此操作:
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;
import org.bson.Document;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.mongodb.MongoClient;
import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
public class Problem {
public static void main(String[] args) {
try (final MongoClient client = new MongoClient()) {
final MongoDatabase db = client.getDatabase("example");
final MongoCollection<Document> collection = db.getCollection("object_arrays");
collection.drop();
final List<Comment> reviews = new ArrayList<Comment>() {
{
add(new Comment("cool guy", new Date(), "John Doe"));
add(new Comment("best joker", new Date(), "Vas Negas"));
add(new Comment("very stupid but very funny man", new Date(), "Bill Murphy"));
}
};
final ObjectMapper mapper = new ObjectMapper();
final User user = new User("0xFF", "email@email.com");
try {
//Create a Document representation of the User object
final String userJson = mapper.writeValueAsString(user);
final Document userDoc = Document.parse(userJson);
//Convert the review ArrayList into a Mongo Document. Need to amend this if not using Java8
final List<Document> reviewDocs = reviews.stream().map(convertToJson())
.map(reviewJson -> Document.parse(reviewJson)).collect(Collectors.toList());
//Wrap it all up to it can be saved to the database
final Document wrapperDoc = new Document();
wrapperDoc.append("user", userDoc).append("reviews", reviewDocs).append("createDate", new Date());
collection.insertOne(wrapperDoc);
} catch (final JsonProcessingException e) {
e.printStackTrace();
}
}
}
private static Function<Comment, String> convertToJson() {
final ObjectMapper mapper = new ObjectMapper();
return review -> {
try {
return mapper.writeValueAsString(review);
} catch (final JsonProcessingException e) {
e.printStackTrace();
}
return "";
};
}
}
*这会使用一些您可能需要更改的Java8代码,具体取决于您使用的Java版本
正如关于这个问题的另一个答案所说,有一些框架可以将对象的序列化和与MongoDB的交互结合起来,这样你就不需要手动编写序列化代码了。例如,Spring有一个Mongo驱动程序,我使用了另一个名为Jongo的驱动程序,我发现它非常好。
答案 1 :(得分:1)
如果您想使用这样的Java对象,Morphia是您最好的选择。现在正在做的工作是支持像你一样尝试的任意Java类,但它还没有完成。