JoinableFactory (druid-processing 28.0.0 API)

All Known Implementing Classes:

FrameBasedInlineJoinableFactory, InlineJoinableFactory, MapJoinableFactory, NoopJoinableFactory
```
public interface JoinableFactory
```
Utility for creating Joinable objects.

See Also:

to register factories, to register factory types with datasource types

Method Summary

All Methods Instance Methods Abstract Methods Default Methods
Modifier and Type	Method	Description
`Optional<Joinable>`	`build(DataSource dataSource, JoinConditionAnalysis condition)`	Create a Joinable object.
`default Optional<byte[]>`	`computeJoinCacheKey(DataSource dataSource, JoinConditionAnalysis condition)`	Compute the cache key for a data source participating in join operation.
`boolean`	`isDirectlyJoinable(DataSource dataSource)`	Returns true if a `Joinable` may be created for a given `DataSource`, but is not a guarantee that `build(org.apache.druid.query.DataSource, org.apache.druid.segment.join.JoinConditionAnalysis)` will return a non-empty result.

- Method Detail
  - isDirectlyJoinable
```
boolean isDirectlyJoinable(DataSource dataSource)
```
    Returns true if a Joinable **may** be created for a given DataSource, but is not a guarantee that build(org.apache.druid.query.DataSource, org.apache.druid.segment.join.JoinConditionAnalysis) will return a non-empty result. Successfully building a Joinable might require specific criteria of the JoinConditionAnalysis.
  - build
```
Optional<Joinable> build(DataSource dataSource,
                         JoinConditionAnalysis condition)
```
    Create a Joinable object. This may be an expensive operation involving loading data, creating a hash table, etc.
    
    Parameters:
    
    dataSource - the datasource to join on
    
    condition - the condition to join on
    
    Returns:
    
    a Joinable if this datasource + condition combo is joinable; empty if not
  - computeJoinCacheKey
```
default Optional<byte[]> computeJoinCacheKey(DataSource dataSource,
                                             JoinConditionAnalysis condition)
```
    Compute the cache key for a data source participating in join operation. This is done separately from {build(DataSource, JoinConditionAnalysis)} which can be an expensive operation and can potentially be avoided if cached results can be used.
    
    Parameters:
    
    dataSource - the datasource to join on
    
    condition - the condition to join on