The QUIC protocol in action: how Uber implemented it to optimize performance

The operation of all platform mechanisms is guaranteed when you use these types. Inherit from BaseIdentityIdEntity if you need to map the entity to a table with IDENTITY primary key. You can implement some of the interfaces Creatable, Versioned, etc. in your concrete entity class.

4.3. The Persistence Interface

Metaclass and metaproperty parameters are determined on the base of the listed annotations parameters as well as field types and class methods.
In “after commit” listeners (TransactionPhase.AFTER_COMMIT), use DataManager or explicitly create a new transaction before using TransactionalDataManager.
This method does not allow modifications of the current persistence context, however, database modifications can be done using QueryRunner.
All materials presented on the open part of this information resource are posted with a delay of at least 15 minutes.
If the disableOnClick attribute is set to true the button will be automatically disabled when clicked, typically to prevent (accidental) extra clicks on a button.

The service interface is located in the global module and is available for both middle and client tiers. At runtime, a proxy is created for the service interface on the client tier. The proxy provides invocation of service bean methods using Spring HTTP Invoker mechanism. In a deployed application, the scripts to create and update the database are located in a special database script directory, that is set by the cuba.dbDir application property. It is also possible to add support for the custom database into the CUBA Studio.

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2.9. Application Properties

CUBA Studio automatically creates database migration scripts for your changing data model, see its documentation. The information below can be helpful for better understanding of the process and for creating Groovy-based migration scripts not supported in Studio. This section provides information on how to configure database connections and work with particular types of DBMS. It also describes a database migration mechanism, which enables creating a new database and keeping it up-to-date throughout the entire cycle of the development and operation of the application.

QUIC protocol in action: how Uber implemented it to optimize performance

And for the Order editor screen, you need to fetch the collection of Items, in addition to that each Item should contain a related Product instance to display its name.
Therefore, if you create an exception instance on Middleware and want to pass it to the client, specify cause parameter only if you are sure that it contains the exceptions known to the client.
When the method is invoked automatically on screen opening, the value of this parameter is false.
An order in which files are declared is important because the values, specified in each subsequent file override the values of the properties with the same name, specified in the preceding files.
Unlike the operations described above, the getConfigValue() operation returns exactly the same value as the corresponding method of the configuration interface invoked in the application code.
The concrete entity class must have a string field annotated with the @Id JPA annotation.
Makes the platform to ignore the user’s time zone (if it is set for the current session) for an attribute of the timestamp type (annotated with @javax.persistence.Temporal.TIMESTAMP).
If an exception is thrown on Middleware as a result of handling a client request, the execution terminates and the exception object is returned to the client.
If the persistence context of a read-only transaction contains modified entities, IllegalStateException will be thrown on attempt to commit the transaction.

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The logic to save these changes in the database should be added separately. GetValue() method of the component returns a string, containing a HEX code of the selected color. ColorPicker is a field that allows a user to preview and select a color. Component returns a hexadecimal (HEX) value of the color as a string. This is a component that allows a user to select multiple values from a list of options using checkboxes.

InitEvent is sent when the screen controller and all its declaratively defined components are created, and dependency injection is completed.
First, wireless networks are susceptible to loss due to interference and signal attenuation.
You can customize the login screen by extending the one provided by the framework or by creating completely new screen from scratch.
The negative impact of soft deletion is increase in database size and likely need for additional cleanup procedures.
If used, the CurrencyField is generated by Studio for this attribute in a Form of the entity editor screen.
According to the example the screen includes the description of customerDc data container for a Customer entity with active attribute.
Indicates that the attribute does not have any length restrictions.

However, these queries can be simpler and faster if related entities are in cache. For example, if you query for Orders together with related Customers and do not use cache, the SQL query will contain a JOIN for customers table. If Customer entities are cached, the SQL query will select only orders, and related customers will be retrieved from the cache.

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Session object can be obtained using the Metadata infrastructure interface. For correct reflection in metadata, the enumeration class must implement the EnumClass interface. Determines related entities handling policy in case of soft deletion of the entity from the inverse side of the relationship. Indicates that the relationship is a composition, which is a stronger variant of the association. Essentially this means that the related entity should only exist as a part of the owning entity, i.e. be created and deleted together with it.

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So if needed, the developer should reload entities with a required view and other parameters.
Generic UI components connected to a datasource get an instance of BeanValidator to check the field value.
In the last example, the exception at point (8) will only occur if the entity supports optimistic locking, i.e. if it implements Versioned interface.
Data components provide a unified interface for binding visual components to entities and for working with entities in screen controllers.
This chapter contains detailed description of the platform architecture, components and mechanisms.
You can adjust the notification type using the cuba.gui.useSaveConfirmation application property.
Keep in mind, that you cannot re-create the SQL Server database from Studio or by executing createDb in the command line, because non-default schema requires association with a user.

In this case, the concrete entity class must have a field of the embeddable type representing the key, annotated with the @EmbeddedId JPA annotation. The above-listed architectural principles are directly reflected in the structure of the assembled application. Suppose we have a simple application which has two blocks – Middleware and Web Client; and includes the functionality of two application components – cuba and reports. Technically, the core framework is also an application component called cuba.

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Besides, LoginPasswordAuthenticationProvider and RememberMeAuthenticationProvider check credentials instance using UserCredentialsChecker beans. There is only one built-in implementation of UserCredentialsChecker interface – BruteForceUserCredentialsChecker that checks if a user uses brute-force attack to find out valid credentials. The default implementation of AuthenticationManager is AuthenticationManagerBean, which delegates authentication to a chain of AuthenticationProvider instances.

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It is possible to group update scripts into subdirectories, however, the path to the script with the subdirectory should not break the chronological sequence. For example, subdirectories can be created by using year, or by year and month. On Microsoft SQL Server, providing a connection property is not enough, you have to link the schema with the database user. Below is an example of creating a new database and using a non-default schema in it.

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Data sources provided via JNDI are configured in a way specific to the application server. CUBA Studio writes connection parameters into modules/core/web/META-INF/context.xml and use this file in the standard deployment process when developing the application. Detection of database constraint violation errors is done by the UniqueConstraintViolationHandler class which uses regular expressions depending on your database type. If the default expression doesn’t recognize errors from your database, try to adjust it using the cuba.uniqueConstraintViolationPattern application property. This interface provides authorization – checking user access rights to different objects in the system. Lazy loading can not help in most cases because data processing is usually performed not in the transaction where the entities were loaded but, for example, on the client tier in UI.

2.13. Bean Validation

Users should be able to view and edit a year, and if a user enters just two digits, the application should transform it to a year between 2000 and 2100. Otherwise, the whole entered number should be accepted as a year. Datatype interface defines methods for converting values to and from strings (formatting and parsing). Each entity attribute, if it is not a reference, has a corresponding Datatype, which is used by the framework to format and parse the attribute value. The usage of JPA cascade and orphanRemoval annotation attributes is not recommended.

2.8. Application Lifecycle Events

Visual Components Library (VCL) contains a large set of ready-to-use components. The fact of whether an entity is cached affects the fetch mode chosen by the platform for loading entity graphs. In the last example, the exception at point (8) will only occur if the entity supports optimistic locking, i.e. if it implements Versioned interface. When working with DataManager, query hints can be provided to the query using LoadContext.setHint() method. A new instance may be passed to EntityManager.persist() to be stored to the database, in which case it changes its state to Managed. Cross-datastore references are also supported by the Filter component.

Attribute access restrictions are applied only to the components bound to single entity attributes, like TextField or LookupField. Table and other components implementing the ListComponent interface are not affected. So if you write a rule that can hide an attribute for some entity instances, we recommend not showing this attribute in tables at all.

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Similar to the Android approach, we have implemented Cronet in Uber iOS apps by intercepting HTTP traffic from network APIusing NSURLProtocol. This abstraction, provided by the iOS Foundation, handles protocol-specific URL data and ensures that we can integrate Cronet into our iOS applications without significant migration costs. Setting up the TCP stack on our heterogeneous edge servers was difficult, as TCP has disparate implementations across OS versions. It was difficult to implement and test various network configurations. Configuring TCP directly on mobile devices was not possible due to lack of permissions.

This event listener can be used for releasing resources acquired by the screen. Class-level annotations on controllers are used to provide information about the screens to the framework. Some of the annotations are applicable to any type of screen, some of them should be used only on entity edit or lookup screens. EntityPersistingEvent is a Spring’s ApplicationEvent which is sent by the framework on the middle tier before a new instance is saved to the database.

An order in which files are declared is important because the values, specified in each subsequent file override the values of the properties with the same name, specified in the preceding files. If you omit + for a property, its value will be obtained only from the current project. It can be useful if you don’t want to inherit some configuration from components, for example, when you define a menu structure. For example, a value specified in a properties file overrides the value specified in the database. You can affect the order of listeners invocation by specifying the @Order annotation. The Events.HIGHEST_PLATFORM_PRECEDENCE and Events.LOWEST_PLATFORM_PRECEDENCE constants define the range which is used by listeners defined in the platform.

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You will also be able to select a data store when using the Generate Model wizard for creation of new entities mapped to an existing database schema. The update scripts for the main data store are located in the /db/update directory of the core module. Update scripts for additional data stores (if any) must be located in /db/update_ directory. You can display entities from different data stores on a single UI screen, and DataManager will ensure they will be dispatched to appropriate data stores on save. Depending on the entity type, DataManager selects a registered data store represented by an implementation of the DataStore interface and delegates loading and saving entities to it. When you control transactions in your code and work with entities via EntityManager, you have to specify explicitly what data store to use.

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Further on, we will consider mainly the middle and client tiers, so the words “all tiers” will refer to these tiers only. The more information on how to work with events, localize messages, provide user access and test your application you can find on the Guides page. The biggest problem is that «bad» bots cost businesses billions of dollars annually through attacks on websites, APIs, and applications. They intercept cheap airline tickets or tickets to concerts first, create artificial shortages of goods, and imitate real people on social media to spread misinformation. Basically, CurrencyField repeats the functionality of TextField.

Any method of the Middleware Spring bean may be annotated with @org.springframework.transaction.annotation.Transactional, which will automatically create a transaction when the method is called.
CUBA-style approach to solving these problems is to detach the value stored in the database from ordinal value of the enumeration.
See the step-by-step guide to working with a custom application component in the Example of Application Component section.
A view is a descriptor of the object graph required for a certain UI screen or data-processing operation.
The update scripts for the main data store are located in the /db/update directory of the core module.
Choosing @Composition annotation as the relationship type enables making use of a special commit mode for datasources in edit screens.
In Figure 2, we have collected the median delays of HTTPS traffic across cells over a range of 2 kilometers.
The information below can be helpful for better understanding of the process and for creating Groovy-based migration scripts not supported in Studio.

This pack consists of 4 files – one for Russian, one for French, one for American English (with US country code), and a default file. See Localization in CUBA applications guide to learn how localized messages within the CUBA application can be defined and used. Applications based on CUBA platform support messages localization, which means that all user interface elements can be displayed in the language, selected by user. To call from a static context, you can use the UuidProvider class, which also https://keyproxy.net/en has an additional fromString() method that works faster than the standard UUID.fromString() method.

As soon as the balancer completes QUIC, our infrastructure explicitly sends this action over HTTP2/TCP to our data centers. Uber is a global scale, namely 600 cities of presence, in each of which the application fully relies on wireless Internet from more than 4500 mobile operators. Users expect the app to be not just fast, but real-time – to deliver this, the Uber app needs low latency and a very reliable connection. Alas, but the stack HTTP / 2 does not perform well in dynamic and lossy wireless networks.