Example JDBC connector#
Примечание
Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.
The Example JDBC connector shows how to extend the base JdbcPlugin
to read data from a source using a JDBC driver, without having
to implement different Trino SPI services, like ConnectorMetadata
or ConnectorRecordSetProvider
.
Примечание
This connector is just an example. It supports a very limited set of data types and does not support any advanced functions, like predicacte or other kind of pushdowns.
Code#
The Example JDBC connector can be found in the trino-example-jdbc directory within the Trino source tree.
Plugin implementation#
The plugin implementation in the Example JDBC connector extends
the JdbcPlugin
class and uses the ExampleClientModule
.
The module:
binds the
ExampleClient
class so it can be used by the base JDBC connector;provides a connection factory that will create new connections using a JDBC driver based on the JDBC URL specified in configuration properties.
JdbcClient implementation#
The base JDBC plugin maps the Trino SPI calls to the JDBC API. Operations like reading table and columns names are well defined in JDBC so the base JDBC plugin can implement it in a way that works for most JDBC drivers.
One behavior that is not implemented by default is mapping of the data types
when reading and writing data. The Example JDBC connector implements
the JdbcClient
interface in the ExampleClient
class that extends
the BaseJdbcClient
and implements two methods.
toColumnMapping#
toColumnMapping
is used when reading data from the connector.
Given a ConnectorSession
, Connection
and a JdbcTypeHandle
,
it returns a ColumnMapping
, if there is a matching data type.
The column mapping includes:
a Trino type,
a write function, used to set query parameter values when preparing a JDBC statement to execute in the data source,
and a read function, used to read a value from the JDBC statement result set, and return it using an internal Trino representation (for example, a Slice).
toWriteMapping#
toWriteMapping
is used when writing data to the connector. Given a
ConnectorSession
and a Trino type, it returns a WriteMapping
.
The mapping includes:
a data type name
a write function