ConnectedDB (D2RQ)

java.lang.Object
- de.fuberlin.wiwiss.d2rq.sql.ConnectedDB

```
public class ConnectedDB
extends Object
```
TODO Move all engine-specific code from here to Vendor and its implementations

Author:

Richard Cyganiak (richard@cyganiak.de), kurtjx (http://github.com/kurtjx)

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`DEFAULT_KEEP_ALIVE_INTERVAL`
`static String`	`DEFAULT_KEEP_ALIVE_QUERY`
`static String`	`KEEP_ALIVE_PROPERTY`
`static String`	`KEEP_ALIVE_QUERY_PROPERTY`

Constructor Summary

Constructors
Constructor and Description
`ConnectedDB(String jdbcURL, String username, String password)`
`ConnectedDB(String jdbcURL, String username, String password, Map<String,DataType.GenericType> columnTypes, int limit, int fetchSize, Properties connectionProperties)`

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`areCompatibleFormats(Attribute column1, Attribute column2)` Checks if two columns are formatted by the database in a compatible fashion.
`void`	`close()` Closes the database connection and shuts down the keep alive agent.
`DataType`	`columnType(Attribute column)` Returns a column's datatype.
`Connection`	`connection()`
`boolean`	`equals(Object otherObject)`
`int`	`fetchSize()`
`protected String`	`getDatabaseProductType()`
`String`	`getJdbcURL()`
`String`	`getPassword()`
`Map<String,List<String>>`	`getUniqueKeyColumns(RelationName tableName)`
`String`	`getUsername()`
`static String`	`guessJDBCDriverClass(String jdbcURL)` Tries to guess the class name of a suitable JDBC driver from a JDBC URL.
`int`	`hashCode()`
`boolean`	`isNullable(Attribute column)`
`int`	`limit()`
`boolean`	`lowerCaseTableNames()` In some situations, MySQL stores table names using lowercase only, and then performs case-insensitive comparison.
`static void`	`registerJDBCDriver(String driverClassName)` Registers a JDBC driver class.
`static void`	`registerJDBCDriverIfPresent(String driverClassName)` Pre-registers a JDBC driver if its class can be found on the classpath.
`DatabaseSchemaInspector`	`schemaInspector()`
`void`	`setDefaultFetchSize(int value)`
`Vendor`	`vendor()`
`boolean`	`vendorIs(Vendor vendor)` Reports the brand of RDBMS.

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - KEEP_ALIVE_PROPERTY
```
public static final String KEEP_ALIVE_PROPERTY
```
    See Also:
    Constant Field Values
  - DEFAULT_KEEP_ALIVE_INTERVAL
```
public static final int DEFAULT_KEEP_ALIVE_INTERVAL
```
    See Also:
    Constant Field Values
  - KEEP_ALIVE_QUERY_PROPERTY
```
public static final String KEEP_ALIVE_QUERY_PROPERTY
```
    See Also:
    Constant Field Values
  - DEFAULT_KEEP_ALIVE_QUERY
```
public static final String DEFAULT_KEEP_ALIVE_QUERY
```
    See Also:
    Constant Field Values
- Constructor Detail
  - ConnectedDB
```
public ConnectedDB(String jdbcURL,
           String username,
           String password)
```
  - ConnectedDB
```
public ConnectedDB(String jdbcURL,
           String username,
           String password,
           Map<String,DataType.GenericType> columnTypes,
           int limit,
           int fetchSize,
           Properties connectionProperties)
```
- Method Detail
  - getJdbcURL
```
public String getJdbcURL()
```
  - getUsername
```
public String getUsername()
```
  - getPassword
```
public String getPassword()
```
  - connection
```
public Connection connection()
```
  - limit
```
public int limit()
```
  - setDefaultFetchSize
```
public void setDefaultFetchSize(int value)
```
  - fetchSize
```
public int fetchSize()
```
  - schemaInspector
```
public DatabaseSchemaInspector schemaInspector()
```
  - columnType
```
public DataType columnType(Attribute column)
```
    Returns a column's datatype. Caches the types for performance.
    
    Parameters:
    column -
    
    Returns:
    The column's datatype, or null if unknown
  - isNullable
```
public boolean isNullable(Attribute column)
```
  - vendorIs
```
public boolean vendorIs(Vendor vendor)
```
    Reports the brand of RDBMS.
    
    Returns:
    true if this database is of the given brand
    See Also:
    TODO make private, use {@link #vendor()} and its methods instead
  - vendor
```
public Vendor vendor()
```
    Returns:
    A helper for generating SQL statements conforming to the syntax of the database engine used in this connection
  - getDatabaseProductType
```
protected String getDatabaseProductType()
                                 throws SQLException
```
    Throws:
    
    SQLException
  - areCompatibleFormats
```
public boolean areCompatibleFormats(Attribute column1,
                           Attribute column2)
```
    Checks if two columns are formatted by the database in a compatible fashion.
    
    Assuming v1 is a value from column1, and v2 a value from column2, and v1 = v2 evaluates to true within the database, then we call the values have compatible formatting if SELECTing them results in character-for-character identical strings. As an example, a TINYINT and a BIGINT are compatible because equal values will be formatted in the same way when SELECTed, e.g. 1 = 1. But if one of them is ZEROFILL, then SELECTing will result in a different character string, e.g. 1 = 0000000001. The two columns wouldn't be compatible.
    
    This is used by the engine when removing unnecessary joins. If two columns have compatible formatting, then we can sometimes use one in place of the other when they are known to have equal values. But not if they are incompatible, because e.g. http://example.org/id/1 is different from http://example.org/id/0000000001.
    
    Returns:
    true if both arguments have compatible formatting
  - getUniqueKeyColumns
```
public Map<String,List<String>> getUniqueKeyColumns(RelationName tableName)
```
  - lowerCaseTableNames
```
public boolean lowerCaseTableNames()
```
    In some situations, MySQL stores table names using lowercase only, and then performs case-insensitive comparison. We need to account for this when comparing table names reported by MySQL and those from the mapping.
    
    See Also:
    MySQL Manual, Identifier Case Sensitivity
  - close
```
public void close()
```
    Closes the database connection and shuts down the keep alive agent.
  - equals
```
public boolean equals(Object otherObject)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object
  - registerJDBCDriverIfPresent
```
public static void registerJDBCDriverIfPresent(String driverClassName)
```
    Pre-registers a JDBC driver if its class can be found on the classpath. If the class is not found, nothing will happen.
    
    Parameters:
    driverClassName - Fully qualified class name of a JDBC driver
  - guessJDBCDriverClass
```
public static String guessJDBCDriverClass(String jdbcURL)
```
    Tries to guess the class name of a suitable JDBC driver from a JDBC URL. This only works in the unlikely case that the driver has been registered earlier using Class.forName(classname).
    
    Parameters:
    jdbcURL - A JDBC URL
    
    Returns:
    The corresponding JDBC driver class name, or null if not known
  - registerJDBCDriver
```
public static void registerJDBCDriver(String driverClassName)
```
    Registers a JDBC driver class.
    
    Parameters:
    driverClassName - Fully qualified class name of a JDBC driver
    
    Throws:
    
    D2RQException - If the class could not be found

Class ConnectedDB

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

KEEP_ALIVE_PROPERTY

DEFAULT_KEEP_ALIVE_INTERVAL

KEEP_ALIVE_QUERY_PROPERTY

DEFAULT_KEEP_ALIVE_QUERY

Constructor Detail

ConnectedDB

ConnectedDB

Method Detail

getJdbcURL

getUsername

getPassword

connection

limit

setDefaultFetchSize

fetchSize

schemaInspector

columnType

isNullable

vendorIs

vendor

getDatabaseProductType

areCompatibleFormats

getUniqueKeyColumns

lowerCaseTableNames

close

equals

hashCode

registerJDBCDriverIfPresent

guessJDBCDriverClass

registerJDBCDriver