Broadly speaking, there are two paths forwards for implementing migrations.
Migration approach 1: Column-based
In this approach, a migration consists of a mapper that provides new values for changed entities on a per-entity basis, for each column; possibly this is then followed up with an arbitrary pass to perform more complicated fixups.
Migration approach 2: Type wrapper-based migration
In this approach, a migration consists of a mapper that converts entities of the old schema to entities of the new schema.
Implementation details vary but would probably look something like:
Specifying new Entity types involves recreating every Schema type on the path from the root to the leaf, which could be very obnoxious for some schemata.
Broadly speaking, there are two paths forwards for implementing migrations.
#### Migration approach 1: Column-based
In this approach, a migration consists of a mapper that provides new values for changed entities on a per-entity basis, for each column; possibly this is then followed up with an arbitrary pass to perform more complicated fixups.
#### Migration approach 2: Type wrapper-based migration
In this approach, a migration consists of a mapper that converts entities of the old schema to entities of the new schema.
Implementation details vary but would probably look something like:
```rust
trait NewWrapper<O: Entity, N: Entity> {
fn map(&mut self, old: O) -> Result<Option<N>>;
}
```
#### Other issues
Specifying new Entity types involves recreating every `Schema` type on the path from the root to the leaf, which could be very obnoxious for some schemata.
kestrel
Broadly speaking, there are two paths forwards for implementing migrations.
Migration approach 1: Column-based
In this approach, a migration consists of a mapper that provides new values for changed entities on a per-entity basis, for each column; possibly this is then followed up with an arbitrary pass to perform more complicated fixups.
Migration approach 2: Type wrapper-based migration
In this approach, a migration consists of a mapper that converts entities of the old schema to entities of the new schema.
Implementation details vary but would probably look something like:
Other issues
Specifying new Entity types involves recreating every
Schematype on the path from the root to the leaf, which could be very obnoxious for some schemata.