Connect to a Db2 database

The JSON API uses JDBC connections to perform various database operations, such as connecting to a Db2 database.

To use the database you must get an instance of a DB object. This object can be initialized with a Connection JDBC connection, or DataSource, or the database URL, user name, and password.

The following snippet from a Java™ program demonstrates how to connect to a Db2 database:

 //Create a context and a dataSource 
 Context initialContext = new InitialContext(); 
 DataSource dataSource = (DataSource)initialContext.lookup("jdbc/myDB2");
 //The dataSource instance becomes a cache key for metadata for the target database 
 DB db = NoSQLClient.getDB(dataSource);

The following overloaded methods are available to get a DB instance:

```
NoSQLClient.getDB(java.sql.Connection)
```

NoSQLClient.getDB(javax.sql.DataSource)

```
NoSQLClient.getDB(String, String, String)
```
The string arguments for the third instance of the getDB method take the following arguments:

jdbcUrl

Specifies a URL that can be used to connect with a JDBC connection.

user

Specifies a user name that can be used to connect the database.

password

Specifies a password.

Note: This DB instance must not be shared between threads. Each thread must make its own NoSQLClient.getDB() method call.

Table 1. Methods on `DB` to control transactional behavior
Method	Description
`public void startTransaction()`	Gets a connection if needed, and sets auto-commit to false. If a connection pool or data source is being used, it puts the `DB` in single connection mode until a future `commitTransaction()` or `rollbackTransaction()`.
`public void commitTransaction()`	Commits a transaction started by `startTransaction()`.
`public void rollbackTransaction()`	Rollback a transaction that was started by `startTransaction()`.
`public void setAutoCommit(boolean autoCommit)`	Sets auto-commit if the Db2 server is using single connection mode. It is an error to call this method in `DataSource` mode.

Note: The transaction APIs described in this table are not applicable for the fire and forget mode.

Obtain a single-mode connection when you are using the transaction APIs to avoid situations where starting a transaction forcibly changes the connection pool mode into single-mode.

Documents are not inserted if an error occurs. With these APIs, either all or none of the documents are inserted.