# SecondaryKeyCreator (Oracle - Berkeley DB Java Edition API)
Date: 2008-04-09

Berkeley DB Java Edition version 3.2.76

## com.sleepycat.je
Interface SecondaryKeyCreator

All Known Implementing Classes:
  SerialSerialKeyCreator, TupleSerialKeyCreator, TupleSerialMarshalledKeyCreator, TupleTupleKeyCreator, TupleTupleMarshalledKeyCreator

    public interface SecondaryKeyCreator

The interface implemented for extracting single-valued secondary keys from primary records.

The key creator object is specified by calling `SecondaryConfig.setKeyCreator`. The secondary database configuration is specified when calling `Environment.openSecondaryDatabase`.

For example:

        class MyKeyCreator implements SecondaryKeyCreator {
            public boolean createSecondaryKey(SecondaryDatabase secondary,
                                                DatabaseEntry key,
                                                DatabaseEntry data,
                                                DatabaseEntry result)
                throws DatabaseException {
                //
                // DO HERE: Extract the secondary key from the primary key and
                // data, and set the secondary key into the result parameter.
                //
                return true;
            }
        }
        ...
        SecondaryConfig secConfig = new SecondaryConfig();
        secConfig.setKeyCreator(new MyKeyCreator());
        // Now pass secConfig to Environment.openSecondaryDatabase

Use this interface when zero or one secondary key is present in a single primary record, in other words, for many-to-one and one-to-one relationships. When more than one secondary key may be present (for many-to-many and one-to-many relationships), use the `SecondaryMultiKeyCreator` interface instead. The table below summarizes how to create all four variations of relationships.

Relationship | Interface | Duplicates | Example
--- | --- | --- | ---
One-to-one | `SecondaryKeyCreator` | No | A person record with a unique social security number key.
Many-to-one | `SecondaryKeyCreator` | Yes | A person record with a non-unique employer key.
One-to-many | `SecondaryMultiKeyCreator` | No | A person record with multiple unique email address keys.
Many-to-many | `SecondaryMultiKeyCreator` | Yes | A person record with multiple non-unique organization keys.

To configure a database for duplicates. pass true to `DatabaseConfig.setSortedDuplicates(boolean)`.

Method Summary
`boolean` `createSecondaryKey(SecondaryDatabase secondary, DatabaseEntry key, DatabaseEntry data, DatabaseEntry result)` Creates a secondary key entry, given a primary key and data entry.

Method Detail

### createSecondaryKey

    boolean createSecondaryKey(SecondaryDatabase secondary,
                               DatabaseEntry key,
                               DatabaseEntry data,
                               DatabaseEntry result)
                               throws DatabaseException

  Creates a secondary key entry, given a primary key and data entry.

  A secondary key may be derived from the primary key, primary data, or a combination of the primary key and data. For secondary keys that are optional, the key creator method may return false and the key/data pair will not be indexed. To ensure the integrity of a secondary database the key creator method must always return the same result for a given set of input parameters.

  Parameters:
    `secondary` - the database to which the secondary key will be added. This parameter is passed for informational purposes but is not commonly used.

    `key` - the primary key entry. This parameter must not be modified by this method.

    `data` - the primary data entry. This parameter must not be modified by this method.

    `result` - the secondary key created by this method.

  Returns:
    true if a key was created, or false to indicate that the key is not present.

  Throws:
    `DatabaseException` - if an error occurs attempting to create the secondary key.

Berkeley DB Java Edition version 3.2.76

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