TAILIEUCHUNG - Apress bắt đầu ứng dụng với java google - p 20

Trong chương này lớn và đóng gói thông tin bạn đã một đi sâu vào kho dữ liệu và sau đó sử dụng những gì bạn đã học để hoàn thành ứng dụng của bạn. Từ cơ sở dữ liệu là một phần không thể thiếu của hầu hết các ứng dụng, nó có giá trị recapping những gì bạn đã học được. Bigtable là một dịch vụ phân phối và khả năng mở rộng cao để lưu trữ và quản lý dữ liệu có cấu trúc | CHAPTER 7 USING THE APP ENGINE DATASTORE Second after the user saves his timecard entries you need to refresh the FlexTable to include the ones that he just entered. In the onSuccess Async method of the saveEntries method add the following call. re-fetch the entries for the current user getCurrentEntries Voilà Your timecard application is now complete. Summary In this large and information-packed chapter you took a deep dive into the datastore and then used what you learned to complete your application. Since databases are an integral part of almost every application it s worth recapping what you ve learned. Bigtable is a highly distributed and scalable service for storing and managing structured data. Bigtable is not a typical relational database that stores records as rows in a table. Instead it stores data as entities with properties organized by application-defined kinds that can be manipulated using either low-level or high-level APIs. Using JDO you can perform common CRUD operations as well as query for entities using JDOQL a SQL-like query language. JDOQL supports filtering sorting and indexing of queries. At a high level Bigtable supports transactions like most relational databases. For the remainder of the chapter the focus was on finishing up your application. First you created an RPC data service that allowed your GWT front end to communicate with the server. You created quite a few classes and interfaces to implement this service as well as the objects that were passed between client and server layers. When you were done you had a complete and working timecard application. In the next chapter we ll focus on some of the functional services available to App Engine 168 C H A P T E R 8 App Engine Services In Chapter 7 you spent a lot of time in the data layer of the application stack. Let s take it up one level and focus on some of the functional services available to App Engine applications. The App Engine JRE has APIs for App Engine .

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