How to extract a nested nullable Avro Schema - avro

Question

The complete schema is the following:
{
"type": "record",
"name": "envelope",
"fields": [
{
"name": "before",
"type": [
"null",
{
"type": "record",
"name": "row",
"fields": [
{
"name": "username",
"type": "string"
},
{
"name": "timestamp",
"type": "long"
}
]
}
]
},
{
"name": "after",
"type": [
"null",
"row"
]
}
]
}
I wanted to programmatically extract the following sub-schema:
{
"type": "record",
"name": "row",
"fields": [
{
"name": "username",
"type": "string"
},
{
"name": "timestamp",
"type": "long"
}
]
}
As you see, field "before" is nullable. I can extract it's schema by doing:
schema.getField("before").schema()
But the schema is not a record as it contains NULL at the beginning(UNION type) and I can't go inside to fetch schema of "row".
["null",{"type":"record","name":"row","fields":[{"name":"username","type":"string"},{"name":"tweet","type":"string"},{"name":"timestamp","type":"long"}]}]
I want to fetch the sub-schema because I want to create GenericRecord out of it. Basically I want to create two GenericRecords "before" and "after" and add them to the main GenericRecord created from full schema.
Any help will be highly appreciated.

Answer 1

Good news, if you have a union schema, you can go inside to fetch the list of possible options:
Schema unionSchema = schema.getField("before").schema();
List<Schema> unionSchemaContains = unionSchema.getTypes();
At that point, you can look inside the list to find the one that corresponds to the Type.RECORD.