Add possibility to unpersist data one generation younger #71
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Allow `Persister` and `Migrator` with version `V` to unpersist data that have not only version `X <= V` but also `V + 1`
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@agemooij did you manage to find few minutes to look at it? |
| @@ -36,40 +36,71 @@ package migrations { | |||
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| /** | |||
| * A `Migrator[R, V]` can migrate raw values of type R from older | |||
| * versions to version `V` by applying a specific `Migration[R]` to it. | |||
| * versions to version `V` or from version one generation younger | |||
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I think it's better to use the word "newer" instead of "younger" to describe Versions with greater numbers than the older ones. It's just a vocabulary clarification, as we had misunderstanding discussing this.
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| } | ||
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| def backFrom[NextV <: Version : VersionInfo](migration: Migration[R])(implicit isNextAfter: IsNextVersionAfter[NextV, V]): Migrator[R, V] = { |
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How about renaming this method to andBackFrom? This way it will gramatically point out that this method should be called only once and at the end of the to method calls:
from[V1](...).to[V2](...).to[V3].andBackFrom[V4](...)
Or even:
from[V1](...).andBackFrom[V4](...)
While this:
from[V1](...).to[V2](...).andBackFrom[V3](...).to[V3](...)
and this:
from[V1](...).to[V2](...).andBackFrom[V3](...).andBackFrom[V4](...)
would automatically look suspicious in code and would be easier to catch in code reviews.
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from[V1](...).to[V2](...).andBackFrom[V3](...).to[V3](...) - this is possible but will have no effect now
from[V1](...).to[V2](...).andBackFrom[V3](...).andBackFrom[V4](...) - this is impossible - will not compile in current version of code
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| /** | ||
| * Creates a JsonPersister[T, V] where V is a version greater than V1. | ||
| * It will always persist instances of T to version V but it will use the specified | ||
| * JsonMigrator[V] to migrate any values older than version V to version V before | ||
| * unpersisting them. | ||
| * JsonMigrator[V] to migrate any values older or or one generation younger |
#57
Allow
PersisterandMigratorwith versionVto unpersist data that have not only versionX <= Vbut alsoV + 1.Possible use-case scenario described in #57 (comment)