[英]How to be avoid duplicates entries at insert to MongoDB
我只是想在将新的DBObject输入数据库时确信它确实是唯一的,并且Collection不包含关键字段重复项。
这是现在的样子:
public abstract class AbstractMongoDAO<ID, MODEL> implements GenericDAO<ID, MODEL> {
protected Mongo client;
protected Class<MODEL> model;
protected DBCollection dbCollection;
/**
* Contains model data : unique key name and name of get method
*/
protected KeyField keyField;
@SuppressWarnings("unchecked")
protected AbstractMongoDAO() {
ParameterizedType genericSuperclass = (ParameterizedType) this.getClass().getGenericSuperclass();
model = (Class<MODEL>) genericSuperclass.getActualTypeArguments()[1];
getKeyField();
}
public void connect() throws UnknownHostException {
client = new MongoClient(Config.getMongoHost(), Integer.parseInt(Config.getMongoPort()));
DB clientDB = client.getDB(Config.getMongoDb());
clientDB.authenticate(Config.getMongoDbUser(), Config.getMongoDbPass().toCharArray());
dbCollection = clientDB.getCollection(getCollectionName(model));
}
public void disconnect() {
if (client != null) {
client.close();
}
}
@Override
public void create(MODEL model) {
Object keyValue = get(model);
try {
ObjectMapper mapper = new ObjectMapper();
String requestAsString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(model);
// check if not presented
BasicDBObject dbObject = new BasicDBObject((String) keyValue, requestAsString);
dbCollection.ensureIndex(dbObject, new BasicDBObject("unique", true));
dbCollection.insert(new BasicDBObject((String) keyValue, requestAsString));
} catch (Throwable e) {
throw new RuntimeException(String.format("Duplicate parameters '%s' : '%s'", keyField.id(), keyValue));
}
}
private Object get(MODEL model) {
Object result = null;
try {
Method m = this.model.getMethod(this.keyField.get());
result = m.invoke(model);
} catch (Exception e) {
throw new RuntimeException(String.format("Couldn't find method by name '%s' at class '%s'", this.keyField.get(), this.model.getName()));
}
return result;
}
/**
* Extract the name of collection that is specified at '@Entity' annotation.
*
* @param clazz is model class object.
* @return the name of collection that is specified.
*/
private String getCollectionName(Class<MODEL> clazz) {
Entity entity = clazz.getAnnotation(Entity.class);
String tableName = entity.value();
if (tableName.equals(Mapper.IGNORED_FIELDNAME)) {
// think about usual logger
tableName = clazz.getName();
}
return tableName;
}
private void getKeyField() {
for (Field field : this.model.getDeclaredFields()) {
if (field.isAnnotationPresent(KeyField.class)) {
keyField = field.getAnnotation(KeyField.class);
break;
}
}
if (keyField == null) {
throw new RuntimeException(String.format("Couldn't find key field at class : '%s'", model.getName()));
}
}
KeyFeld是自定义注释:
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface KeyField {
String id();
String get();
String statusProp() default "ALL";
但是我不确定该解决方案是否能证明这一点。 我刚来蒙哥。
有什么建议么?
可以使用_id
字段在MonboDb中维护唯一性。 如果我们不提供此字段的值,则MongoDB会自动为该微粒集合创建一个唯一的ID。
因此,在您的情况下,只需在Java中创建一个名为_id
的属性,然后在此处分配您唯一的字段值即可。 如果重复,它将引发异常。
使用Spring Data MongoDB(这个问题用spring-data
标记,这就是我建议的原因),您需要做的就是:
// Your types
class YourType {
BigInteger id;
@Indexed(unique = true) String emailAddress;
…
}
interface YourTypeRepository extends CrudRepository<YourType, BigInteger> { }
// Infrastructure setup, if you use Spring as container prefer @EnableMongoRepositories
MongoOperations operations = new MongoTemplate(new MongoClient(), "myDatabase");
MongoRepositoryFactory factory = new MongoRepositoryFactory(operations);
YourTypeRepository repository = factory.getRepository(YourTypeRepository.class);
// Now use it…
YourType first = …; // set email address
YourType second = …; // set same email address
repository.save(first);
repository.save(second); // will throw an exception
与原始问题最相关的关键部分是@Indexed
因为这将导致在创建存储库时创建所需的唯一索引。
您所获得的是:
有关更多详细信息,请参阅参考文档 。
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