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The Apache MetaModel JDBC module is built such that we use as much of the powerful SQL capabilities of JDBC databases as possible (see Query execution strategies). So as such the module does little, except translate JDBC into the MetaModel API, but on the other hand it provides a single interface which translates into any of the many SQL dialects that are out there.

Features of the connector includes:

  • Full implementation of DataContext and UpdateableDataContext.
  • Mapping of MetaModel's data types to the particular set of data types available for the database. For instance MetaModel's STRING will be automatically converted to 'VARCHAR', 'TEXT' etc. depending on the database.
  • Automatic formatting and narrowing of values when interacting with the database.
  • Contains specialization and optimization for many databases, including:
    • PostgreSQL
    • MySQL
    • Microsoft SQL Server
    • Oracle
    • IBM DB2
    • Apache Hive
    • H2
    • SQLite
    • Hsqldb
    • Apache Derby
  • Support for JDBC batch operations when you use BatchUpdateScript.
  • Support for reusable prepared statements (as "compiled queries" in MetaModel).
  • Works with single Connections or connection pools (DataSource)

Creating from plain old java code - JdbcDataContext

This is really simple:

 

Connection conn = DriverManager.getConnection(...); 
DataContext dataContext = new JdbcDataContext(conn);

Creating from properties - JdbcDataContextFactory

If you wish to construct your JDBC DataContext from properties, this is also possible. For instance:

 

final DataContextPropertiesImpl properties = new DataContextPropertiesImpl();
properties.put("type", "jdbc");
properties.put("url", "jdbc:postgresql://localhost:5432/mydb");
 
DataContext dataContext = DataContextFactoryRegistryImpl.getDefaultInstance().createDataContext(properties);

 

The relevant properties for this type of instantiation are:

Property
Example value
Required
Description
type
jdbc
(tick)Must be set to 'jdbc' or else another type of DataContext will be constructed.
url
jdbc:mysql://localhost/sakila
(tick)The JDBC URL to use.
driver-class
com.mysql.jdbc.Driver
 The JDBC driver class name.
username
johndoe
 The username to use when connecting.
password
qwerty
 The password to use when connecting.
table-types
TABLE,VIEW
 A comma-separated list of table types to include in JDBC metadata discovery.
catalog
cat01
 The JDBC 'catalog' value

Additional behaviour configuration

The module contains a few features that are specific to the JDBC interactions. These are all configured as Java system properties.

System propertyDefault valueDescription
metamodel.jdbc.convert.lobs
"false"
Whether or not to automatically convert CLOBs into String and BLOBs into byte[].
metamodel.jdbc.batch.updates
DatabaseMetaData.supportsBatchUpdates()
Whether or not using the JDBC batch API should be allowed. Set to "true" or "false" to override the default dynamic behavior.
metamodel.jdbc.compiledquery.pool.max.size
-1
The maximum number of open prepared statements to keep in a pool for the compiled queries.
metamodel.jdbc.compiledquery.pool.idle.timeout
500
The minimum idle timeout before a prepared statement is marked as evictable.
metamodel.jdbc.compiledquery.pool.eviction.period.millis
1000
The time between eviction runs in the compiled queries pool.
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