# Interface SQLData

public interface SQLData
The interface used for the custom mapping of an SQL user-defined type (UDT) to a class in the Java programming language. The class object for a class implementing the `SQLData` interface will be entered in the appropriate `Connection` object's type map along with the SQL name of the UDT for which it is a custom mapping.

Typically, a `SQLData` implementation will define a field for each attribute of an SQL structured type or a single field for an SQL `DISTINCT` type. When the UDT is retrieved from a data source with the `ResultSet.getObject` method, it will be mapped as an instance of this class. A programmer can operate on this class instance just as on any other object in the Java programming language and then store any changes made to it by calling the `PreparedStatement.setObject` method, which will map it back to the SQL type.

It is expected that the implementation of the class for a custom mapping will be done by a tool. In a typical implementation, the programmer would simply supply the name of the SQL UDT, the name of the class to which it is being mapped, and the names of the fields to which each of the attributes of the UDT is to be mapped. The tool will use this information to implement the `SQLData.readSQL` and `SQLData.writeSQL` methods. The `readSQL` method calls the appropriate `SQLInput` methods to read each attribute from an `SQLInput` object, and the `writeSQL` method calls `SQLOutput` methods to write each attribute back to the data source via an `SQLOutput` object.

An application programmer will not normally call `SQLData` methods directly, and the `SQLInput` and `SQLOutput` methods are called internally by `SQLData` methods, not by application code.

Since:
  1.2

- ## Method Summary

  Modifier and Type
  Method
  Description
  `String`
  `getSQLTypeName()`
  Returns the fully-qualified name of the SQL user-defined type that this object represents.
  `void`
  `readSQL(SQLInput stream, String typeName)`
  Populates this object with data read from the database.
  `void`
  `writeSQL(SQLOutput stream)`
  Writes this object to the given SQL data stream, converting it back to its SQL value in the data source.

- ## Method Details

  - ### getSQLTypeName

    String getSQLTypeName() throws SQLException
    Returns the fully-qualified name of the SQL user-defined type that this object represents. This method is called by the JDBC driver to get the name of the UDT instance that is being mapped to this instance of `SQLData`.
    Returns:
      the type name that was passed to the method `readSQL` when this object was constructed and populated
    Throws:
      `SQLException` - if there is a database access error
      `SQLFeatureNotSupportedException` - if the JDBC driver does not support this method
    Since:
      1.2

  - ### readSQL

    void readSQL(SQLInput stream, String typeName) throws SQLException
    Populates this object with data read from the database. The implementation of the method must follow this protocol:
    - It must read each of the attributes or elements of the SQL type from the given input stream. This is done by calling a method of the input stream to read each item, in the order that they appear in the SQL definition of the type.
    - The method `readSQL` then assigns the data to appropriate fields or elements (of this or other objects). Specifically, it must call the appropriate reader method (`SQLInput.readString`, `SQLInput.readBigDecimal`, and so on) method(s) to do the following: for a distinct type, read its single data element; for a structured type, read a value for each attribute of the SQL type.
    The JDBC driver initializes the input stream with a type map before calling this method, which is used by the appropriate `SQLInput` reader method on the stream.
    Parameters:
      `stream` - the `SQLInput` object from which to read the data for the value that is being custom mapped
      `typeName` - the SQL type name of the value on the data stream
    Throws:
      `SQLException` - if there is a database access error
      `SQLFeatureNotSupportedException` - if the JDBC driver does not support this method
    Since:
      1.2
    See Also:
      - `SQLInput`

  - ### writeSQL

    void writeSQL(SQLOutput stream) throws SQLException
    Writes this object to the given SQL data stream, converting it back to its SQL value in the data source. The implementation of the method must follow this protocol:
    It must write each of the attributes of the SQL type to the given output stream. This is done by calling a method of the output stream to write each item, in the order that they appear in the SQL definition of the type. Specifically, it must call the appropriate `SQLOutput` writer method(s) (`writeInt`, `writeString`, and so on) to do the following: for a Distinct Type, write its single data element; for a Structured Type, write a value for each attribute of the SQL type.
    Parameters:
      `stream` - the `SQLOutput` object to which to write the data for the value that was custom mapped
    Throws:
      `SQLException` - if there is a database access error
      `SQLFeatureNotSupportedException` - if the JDBC driver does not support this method
    Since:
      1.2
    See Also:
      - `SQLOutput`