org.apache.spark.sql.jdbc

Class JdbcDialect

Object

org.apache.spark.sql.jdbc.JdbcDialect

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

AggregatedDialect

public abstract class JdbcDialect
extends Object
implements scala.Serializable

:: DeveloperApi :: Encapsulates everything (extensions, workarounds, quirks) to handle the SQL dialect of a certain database or jdbc driver. Lots of databases define types that aren't explicitly supported by the JDBC spec. Some JDBC drivers also report inaccurate information---for instance, BIT(n>1) being reported as a BIT type is quite common, even though BIT in JDBC is meant for single-bit values. Also, there does not appear to be a standard name for an unbounded string or binary type; we use BLOB and CLOB by default but override with database-specific alternatives when these are absent or do not behave correctly.

Currently, the only thing done by the dialect is type mapping. getCatalystType is used when reading from a JDBC table and getJDBCType is used when writing to a JDBC table. If getCatalystType returns null, the default type handling is used for the given JDBC type. Similarly, if getJDBCType returns (null, None), the default type handling is used for the given Catalyst type.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
JdbcDialect()

Method Summary

Modifier and Type	Method and Description
void	beforeFetch(java.sql.Connection connection, scala.collection.immutable.Map<String,String> properties) Override connection specific properties to run before a select is made.
abstract boolean	canHandle(String url) Check if this dialect instance can handle a certain jdbc url.
Object	compileValue(Object value) Converts value to SQL expression.
scala.Option<DataType>	getCatalystType(int sqlType, String typeName, int size, MetadataBuilder md) Get the custom datatype mapping for the given jdbc meta information.
scala.Option<JdbcType>	getJDBCType(DataType dt) Retrieve the jdbc / sql type for a given datatype.
String	getSchemaQuery(String table) The SQL query that should be used to discover the schema of a table.
String	getTableExistsQuery(String table) Get the SQL query that should be used to find if the given table exists.
String	getTruncateQuery(String table) The SQL query that should be used to truncate a table.
scala.Option<Object>	isCascadingTruncateTable() Return Some[true] iff TRUNCATE TABLE causes cascading default.
String	quoteIdentifier(String colName) Quotes the identifier.

Methods inherited from class Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JdbcDialect

public JdbcDialect()

Method Detail

canHandle

public abstract boolean canHandle(String url)

Check if this dialect instance can handle a certain jdbc url.

Parameters:

url - the jdbc url.

Returns:

True if the dialect can be applied on the given jdbc url.

Throws:

NullPointerException - if the url is null.

getCatalystType

public scala.Option<DataType> getCatalystType(int sqlType,
                                              String typeName,
                                              int size,
                                              MetadataBuilder md)

Get the custom datatype mapping for the given jdbc meta information.

Parameters:

sqlType - The sql type (see java.sql.Types)

typeName - The sql type name (e.g. "BIGINT UNSIGNED")

size - The size of the type.

md - Result metadata associated with this type.

Returns:

The actual DataType (subclasses of DataType) or null if the default type mapping should be used.

getJDBCType

public scala.Option<JdbcType> getJDBCType(DataType dt)

Retrieve the jdbc / sql type for a given datatype.

Parameters:

dt - The datatype (e.g. StringType)

Returns:

The new JdbcType if there is an override for this DataType

quoteIdentifier

public String quoteIdentifier(String colName)

Quotes the identifier. This is used to put quotes around the identifier in case the column name is a reserved keyword, or in case it contains characters that require quotes (e.g. space).

Parameters:

colName - (undocumented)

Returns:

(undocumented)

getTableExistsQuery

public String getTableExistsQuery(String table)

Get the SQL query that should be used to find if the given table exists. Dialects can override this method to return a query that works best in a particular database.

Parameters:

table - The name of the table.

Returns:

The SQL query to use for checking the table.

getSchemaQuery

public String getSchemaQuery(String table)

The SQL query that should be used to discover the schema of a table. It only needs to ensure that the result set has the same schema as the table, such as by calling "SELECT * ...". Dialects can override this method to return a query that works best in a particular database.

Parameters:

table - The name of the table.

Returns:

The SQL query to use for discovering the schema.

getTruncateQuery

public String getTruncateQuery(String table)

The SQL query that should be used to truncate a table. Dialects can override this method to return a query that is suitable for a particular database. For PostgreSQL, for instance, a different query is used to prevent "TRUNCATE" affecting other tables.

Parameters:

table - The name of the table.

Returns:

The SQL query to use for truncating a table

beforeFetch

public void beforeFetch(java.sql.Connection connection,
                        scala.collection.immutable.Map<String,String> properties)

Override connection specific properties to run before a select is made. This is in place to allow dialects that need special treatment to optimize behavior.

Parameters:

connection - The connection object

properties - The connection properties. This is passed through from the relation.

compileValue

public Object compileValue(Object value)

Converts value to SQL expression.

Parameters:

value - The value to be converted.

Returns:

Converted value.

isCascadingTruncateTable

public scala.Option<Object> isCascadingTruncateTable()

Return Some[true] iff TRUNCATE TABLE causes cascading default. Some[true] : TRUNCATE TABLE causes cascading. Some[false] : TRUNCATE TABLE does not cause cascading. None: The behavior of TRUNCATE TABLE is unknown (default).

Returns:

(undocumented)