[AVRO-1347] Improve name and alias matching for named schemas

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: java
• Assignee: Unassigned
• Reporter: Vincenz Priesnitz
• Created: 12/Jun/13 18:34
• Updated: 09/Feb/17 08:55

Description

When reading an avro file with a named schema, the aliases of the writers schema are not taken into account; only the aliases of the readers are matched against the writers name. Even if the writers aliases match the readers name, the schemas will not be matched.

For example, the following two enum schemas will not be matched, even though they share a common alias.

{
	"type"  : "enum",
	"name"  : "foo",
	"alias" : "CommonAlias",
	"symbols" : ["LEFT", "RIGHT"]

}

{
	"type"  : "enum",
	"name"  : "bar",
	"alias" : "CommonAlias",
	"symbols" : ["LEFT", "RIGHT"]

}

In most cases, the DatumReader resolves records of different names or namespaces by matching their fields.
Unfortunately, there are some cases, where this sort of matching is not happening, but just the names are compared:

• Other named nodes, like enums, fixed or fieldschemas are not matched this way.
• A record inside a union is also only matched by the full name.

The latter one is especially tricky, since two recordschemas that match structurally but differ in name or space, are interexchangable until they are put into an union, at which point an exception is thrown.

I propose that two named schemas are matched, when they share a common name or alias.
I implemented said changes and added a java annotation @AvroAlias(alias, space) that allows one to add an alias to a record, enum or field.

Issue Links

• relates to: AVRO-1340 use default to allow old readers to specify default enum value when encountering new enum symbols