Experiments with evolving Avro schemas, using fastavro for serialization and deserialization.

Determine how Avro handles differences in writer and reader schemas.

From a reader schema perspective:

• Which differences with writer schema are allowed?

• Which differences with the writer schema would raise an error?

1. Adding a default value to a field makes it "optional".

   • A reader schema may include new fields, with defaults, and still be able to read data from the writer schema that does not have the field (reader made a backwards compatible change).
   • If the reader schema does not include a field that the writer has added and specified a default, the reader can still read it (writer made a forwards compatible change).

2. Fields are considered "required" unless a default is specified.

   • A reader cannot add a required field in a backwards-compatible manner.
   • A reader can remove a required field in a backwards-compatible manner.
   • A writer may add a new required field and still be considered a forwards-compatible change.

3. Setting a field's type to a union of "null" and one or more other types, means it is "nullable" (can contain null, i.e. None in Python), but does not make it optional.

pip install -r requirements.txt

pytest