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Berkeley DB Java Edition version 3.3.87 |
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public interface SecondaryMultiKeyCreator
The interface implemented for extracting multi-valued secondary keys from primary records.
The key creator object is specified by calling SecondaryConfig.setMultiKeyCreator. The
secondary database configuration is specified when calling Environment.openSecondaryDatabase.
For example:
class MyMultiKeyCreator implements SecondaryMultiKeyCreator {
public void createSecondaryKeys(SecondaryDatabase secondary,
DatabaseEntry key,
DatabaseEntry data,
Set<DatabaseEntry> results)
throws DatabaseException {
//
// DO HERE: Extract the secondary keys from the primary key and
// data. For each key extracted, create a DatabaseEntry and add it
// to the results set.
//
}
}
...
SecondaryConfig secConfig = new SecondaryConfig();
secConfig.setMultiKeyCreator(new MyMultiKeyCreator());
// Now pass secConfig to Environment.openSecondaryDatabase
Use this interface when any number of secondary keys may be present in a
single primary record, in other words, for many-to-many and one-to-many
relationships. When only zero or one secondary key is present (for
many-to-one and one-to-one relationships) you may use the SecondaryKeyCreator 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).
Note that SecondaryMultiKeyCreator may also be used for
single key secondaries (many-to-one and one-to-one); in this case, at most a
single key is added to the results set.
SecondaryMultiKeyCreator is only slightly less efficient than
SecondaryKeyCreator in that two or three temporary sets must be
created to hold the results. @see SecondaryConfig
| Method Summary | |
|---|---|
void |
createSecondaryKeys(SecondaryDatabase secondary,
DatabaseEntry key,
DatabaseEntry data,
Set<DatabaseEntry> results)
Creates a secondary key entry, given a primary key and data entry. |
| Method Detail |
|---|
void createSecondaryKeys(SecondaryDatabase secondary,
DatabaseEntry key,
DatabaseEntry data,
Set<DatabaseEntry> results)
throws DatabaseException
A secondary key may be derived from the primary key, primary data, or a combination of the primary key and data. Zero or more secondary keys may be derived from the primary record and returned in the results parameter. To ensure the integrity of a secondary database the key creator method must always return the same results for a given set of input 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.results - the set to contain the the secondary key DatabaseEntry
objects created by this method.
DatabaseException - if an error occurs attempting to create the
secondary key.
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