leo-vital commented on issue #252:
URL: https://github.com/apache/avro-rs/issues/252#issuecomment-3177888121
> It would be easier to discuss if you provide sample writer (before) schema
and reader (after) schema. If I understand you correctly you ask whether you
can derive the reader schema with `AvroSchema`. Correct ? Let's see how it
looks like and then we can answer!
@martin-g Let's say this is the struct:
```rust
#[derive(AvroSchema)]
struct Book {
title: String,
}
```
And the schema generated from that ends up looking like this:
```
{"subject":"book-schema-value",
"version":1,
"id":1,
"schema":"
{\"type\":\"record\",
\"name\":\"Book\",
\"fields\":[{\"name\":\"title\",\"type\":\"string\"}]}"}
```
So let's say we register that schema as the initial version of the schema,
in the Schema Registry. Then we want to add an optional new field to the struct:
```rust
#[derive(AvroSchema)]
struct Book {
title: String,
subtitle: Option<String>,
}
```
The generated schema will look like this:
```
{"subject":"book-schema-value",
"version":1,
"id":1,
"schema":"
{\"type\":\"record\",
\"name\":\"Book\",
\"fields\":[{\"name\":\"title\",\"type\":\"string\"},
{\"name\":\"subtitle\",\"type\":[\"null\",\"string\"]}]}"}
```
And when trying to register that as a new version of the schema in the
Registry, the aformentioned `READER_FIELD_MISSING_DEFAULT_VALUE` error will
happen in the Registry.
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