Package org.apache.avro

Class Resolver

java.lang.Object

org.apache.avro.Resolver

public class Resolver
extends Object

Encapsulate schema-resolution logic in an easy-to-consume representation. See resolve(org.apache.avro.Schema, org.apache.avro.Schema, org.apache.avro.generic.GenericData) and also the separate document entitled refactoring-resolution for more information. It might also be helpful to study ResolvingGrammarGenerator as an example of how to use this class.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	Resolver.Action	An abstract class for an action to be taken to resolve a writer's schema (found in public instance variable writer) against a reader's schema (in reader).
static class	Resolver.Container	Used for array and map schemas: the public instance variable elementAction contains the resolving action needed for the element type of an array or value top of a map.
static class	Resolver.DoNothing	In this case, there's nothing to be done for resolution: the two schemas are effectively the same.
static class	Resolver.EnumAdjust	Contains information needed to resolve enumerations.
static class	Resolver.ErrorAction	In this case there is an error.
static class	Resolver.Promote	In this case, the writer's type needs to be promoted to the reader's.
static class	Resolver.ReaderUnion	In this case, the reader is a union and the writer is not.
static class	Resolver.RecordAdjust	Instructions for resolving two record schemas.
static class	Resolver.Skip	This only appears inside Resolver.RecordAdjust.fieldActions, i.e., the actions for adjusting the fields of a record.
static class	Resolver.WriterUnion	In this case, the writer was a union.

Constructor Summary

Constructors

Constructor	Description
Resolver()

Method Summary

Modifier and Type	Method	Description
static Resolver.Action	resolve(Schema writer, Schema reader)	Uses GenericData.get() for the data param.
static Resolver.Action	resolve(Schema writer, Schema reader, GenericData data)	Returns a Resolver.Action tree for resolving the writer schema writer and the reader schema reader.

Methods inherited from class java.lang.Object

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

Constructor Details

Resolver

public Resolver()

Method Details

resolve

public static Resolver.Action resolve(Schema writer,
 Schema reader,
 GenericData data)

Returns a Resolver.Action tree for resolving the writer schema writer and the reader schema reader. This method walks the reader's and writer's schemas together, generating an appropriate subclass of Resolver.Action to encapsulate the information needed to resolve the corresponding parts of each schema tree. For convenience, every Resolver.Action object has a pointer to the corresponding parts of the reader's and writer's trees being resolved by the action. Each subclass of Resolver.Action has additional information needed for different types of schema, e.g., the Resolver.EnumAdjust subclass has information about re-ordering and deletion of enumeration symbols, while Resolver.RecordAdjust has information about re-ordering and deletion of record fields. Note that aliases are applied to the writer's schema before resolution actually takes place. This means that the writer field of the resulting Resolver.Action objects will not be the same schema as provided to this method. However, the reader field will be.

Parameters:

writer - The schema used by the writer

reader - The schema used by the reader

data - Used for getDefaultValue and getting conversions

Returns:

Nested actions for resolving the two

resolve

public static Resolver.Action resolve(Schema writer,
 Schema reader)

Uses GenericData.get() for the data param.