ENG 08 0 Database General
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Drogon has built-in database read/write engine. The operation of database connection is based on non-blocking I/O technology. Therefore, the application works in an efficient non-blocking asynchronous mode from the bottom to the upper layer, which ensures Drogon's high concurrency performance. Currently, Drogon supports PostgreSQL and MySQL databases. If you want to use a database, the development environment of the corresponding database must be installed first. Drogon will automatically detect the header files and library files of these libraries and compile the corresponding parts. For the preparation of the database development environment, see Development Environment.
Drogon supports the sqlite3 database in order to support lightweight applications. The asynchronous interface is implemented through the thread pool, which is the same as the interfaces of the aforementioned databases.
The basic class of Drogon's database is DbClient (this is an abstract class, the specific type depends on the interface that constructs it). Unlike a generic database interface, a DbClient object does not represent a single database connection. It can contain one or more database connections, so you can think of it as a connection pool object.
DbClient provides both synchronous and asynchronous interfaces. The asynchronous interface also supports both blocking and non-blocking modes. Of course, for the cooperation with the Drogon asynchronous framework, it is recommended that you use the the asynchronous interface with non-blocking mode.
Usually, when an asynchronous interface is called, DbClient will randomly select one of the idle connections it manages to perform related query operations. When the result returns, DbClient will process the data and return it to the caller through the callback function object; Without an idle connection, the execution content will be cached. Once a connection has executed its own sql request, the pending command will be fetched from the cache to execute.
For details on DbClient, see DbClient.
The transaction object can be generated by DbClient to support transaction operations. In addition to the extra rollback() interface, the transaction object is basically the same as DbClient. The transaction class is Transaction. For details of the Transaction class, see Transaction.
Drogon also provides support for ORM. Users can use the drogon_ctl command to read the tables in the database and generate the corresponding model source code. Then, execute the database operations of these models through the Mapper<MODEL> class template. Mapper provides simple and convenient interfaces for standard database operations, allowing users to make the additions, deletions, and changes to the table without writing sql statements. For ORM, please refer to ORM
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