如何避免在插入MongoDB時出現重復項

Question

我只是想在將新的DBObject輸入數據庫時​​確信它確實是唯一的，並且Collection不包含關鍵字段重復項。

這是現在的樣子：

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是自定義注釋：

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface KeyField {

    String id();

    String get();

    String statusProp() default "ALL";

但是我不確定該解決方案是否能證明這一點。 我剛來蒙哥。

有什么建議么？

Answer 1

可以使用_id字段在MonboDb中維護唯一性。 如果我們不提供此字段的值，則MongoDB會自動為該微粒集合創建一個唯一的ID。

因此，在您的情況下，只需在Java中創建一個名為_id的屬性，然后在此處分配您唯一的字段值即可。 如果重復，它將引發異常。

Answer 2

使用Spring Data MongoDB（這個問題用spring-data標記，這就是我建議的原因），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

與原始問題最相關的關鍵部分是@Indexed因為這將導致在創建存儲庫時創建所需的唯一索引。

您所獲得的是：

• 無需手動實現任何存儲庫（已刪除的代碼不包含錯誤\\ o /）
• 自動對象到文檔的轉換
• 自動索引創建
• 強大的存儲庫抽象，可通過聲明查詢方法輕松查詢數據

有關更多詳細信息，請參閱參考文檔 。