我已经创建了一个类 User
来扩展 Document
。 User
只有一些简单的构造函数和围绕一些字符串和整数的 getter/setter。但是,当我尝试将 User 类插入 Mongo 时,出现以下错误:
Exception in thread "main" org.bson.codecs.configuration.CodecConfigurationException: Can't find a codec for class com.foo.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.ProvidersCodecRegistry.get(ProvidersCodecRegistry.java:37)
at org.bson.BsonDocumentWrapper.asBsonDocument(BsonDocumentWrapper.java:62)
at com.mongodb.MongoCollectionImpl.documentToBsonDocument(MongoCollectionImpl.java:507)
at com.mongodb.MongoCollectionImpl.insertMany(MongoCollectionImpl.java:292)
at com.mongodb.MongoCollectionImpl.insertMany(MongoCollectionImpl.java:282)
at com.foo.bar.main(bar.java:27)
听起来我需要使用一些 Mongo 编解码器的东西,但我不熟悉它,一些快速谷歌搜索返回一些看起来非常高级的结果。
如何正确编写用于 Mongo 的 User
类?这是我的类(class)供引用:
public class User extends Document {
User(String user, List<Document > history, boolean isActive, String location){
this.append("_id", user)
.append("history", history)
.append("isActive", isActive)
.append("location", location);
}
public List<Document > getHistory(){
return this.get("history", ArrayList.class);
}
public void addToHistory(Document event){
List<Document> history = this.getHistory();
history.add(event);
this.append("history", history);
}
public boolean hasMet(User otherUser){
List<String> usersIveMet = this.getUsersMet(),
usersTheyMet = otherUser.getUsersMet();
return !Collections.disjoint(usersIveMet, usersTheyMet);
}
public List<String> getUsersMet() {
List<Document> usersHistory = this.getHistory();
List<String> usersMet = usersHistory.stream()
.map(doc -> Arrays.asList(doc.getString("user1"), doc.getString("user1")))
.filter(u -> !u.equals(this.getUser()))
.flatMap(u -> u.stream())
.collect(Collectors.toList());
return usersMet;
}
public String getUser(){
return this.getString("_id");
}
}
最佳答案
由于您正在尝试创建新对象(即使您从 Document 扩展),Mongo 无法识别它,因此您需要提供编码/解码以便让 Mongo 了解您的对象(至少我看不到其他方式..)。
我试了一下你的 User 类,让它工作了。 所以,这是我定义用户类的方式:
public class User {
private List<Document> history;
private String id;
private Boolean isActive;
private String location;
// Getters and setters. Omitted for brevity..
}
然后你需要为你的用户类提供编码/解码逻辑:
public class UserCodec implements Codec<User> {
private CodecRegistry codecRegistry;
public UserCodec(CodecRegistry codecRegistry) {
this.codecRegistry = codecRegistry;
}
@Override
public User decode(BsonReader reader, DecoderContext decoderContext) {
reader.readStartDocument();
String id = reader.readString("id");
Boolean isActive = reader.readBoolean("isActive");
String location = reader.readString("location");
Codec<Document> historyCodec = codecRegistry.get(Document.class);
List<Document> history = new ArrayList<>();
reader.readStartArray();
while (reader.readBsonType() != BsonType.END_OF_DOCUMENT) {
history.add(historyCodec.decode(reader, decoderContext));
}
reader.readEndArray();
reader.readEndDocument();
User user = new User();
user.setId(id);
user.setIsActive(isActive);
user.setLocation(location);
user.setHistory(history);
return user;
}
@Override
public void encode(BsonWriter writer, User user, EncoderContext encoderContext) {
writer.writeStartDocument();
writer.writeName("id");
writer.writeString(user.getId());
writer.writeName("isActive");
writer.writeBoolean(user.getIsActive());
writer.writeName("location");
writer.writeString(user.getLocation());
writer.writeStartArray("history");
for (Document document : user.getHistory()) {
Codec<Document> documentCodec = codecRegistry.get(Document.class);
encoderContext.encodeWithChildContext(documentCodec, writer, document);
}
writer.writeEndArray();
writer.writeEndDocument();
}
@Override
public Class<User> getEncoderClass() {
return User.class;
}
}
那么在开始序列化/反序列化之前,你需要一个编解码器来进行类型检查。
public class UserCodecProvider implements CodecProvider {
@Override
@SuppressWarnings("unchecked")
public <T> Codec<T> get(Class<T> clazz, CodecRegistry registry) {
if (clazz == User.class) {
return (Codec<T>) new UserCodec(registry);
}
return null;
}
}
最后,您需要将您的提供商注册到您的 MongoClient,仅此而已。
public class MongoDb {
private MongoDatabase db;
public MongoDb() {
CodecRegistry codecRegistry = CodecRegistries.fromRegistries(
CodecRegistries.fromProviders(new UserCodecProvider()),
MongoClient.getDefaultCodecRegistry());
MongoClientOptions options = MongoClientOptions.builder()
.codecRegistry(codecRegistry).build();
MongoClient mongoClient = new MongoClient(new ServerAddress(), options);
db = mongoClient.getDatabase("test");
}
public void addUser(User user) {
MongoCollection<User> collection = db.getCollection("user").withDocumentClass(User.class);
collection.insertOne(user);
}
public static void main(String[] args) {
MongoDb mongoDb = new MongoDb();
Document history1 = new Document();
history1.append("field1", "value1");
history1.append("field2", "value2");
history1.append("field3", "value3");
List<Document> history = new ArrayList<>();
history.add(history1);
User user = new User();
user.setId("someId1");
user.setIsActive(true);
user.setLocation("someLocation");
user.setHistory(history);
mongoDb.addUser(user);
}
}
关于java - 如何正确扩展 Mongo 的文档类?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/33326572/