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Gavin 2023-05-13 19:52:53 +02:00 committed by Christian Beikov
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@ -15,16 +15,34 @@ This is called _bottom up_ mapping.
// ."Legacy" data
====
Developers often refer to a pre-existing relational database as "legacy" data.
That's perhaps a bad word to use, conjuring images of bad old "legacy apps" written in COBOL or something.
But it's not "legacy" data—it's just your data.
And it's valuable.
So learning to work with "legacy" data is important.
This tends to conjure images of bad old "legacy apps" written in COBOL or something.
But legacy data is valuable, and learning to work with it is important.
====
Especially when mapping bottom up, we often need to customize the inferred object/relational mappings.
This is a somewhat tedious topic, and so we don't want to spend too many words on it.
Instead, we'll quickly skim the most important mapping annotations.
[[case-convention]]
.Hibernate SQL case convention
****
Computers have had lowercase letters for rather a long time now.
Most developers learned long ago that text written in MixedCase, camelCase, or even snake_case is easier to read than text written in SHOUTYCASE.
This is just as true of SQL as it is of any other language.
Therefore, for over twenty years, the convention on the Hibernate project has been that:
- query language identifiers are written in `lowercase`,
- table names are written in `MixedCase`, and
- column names are written in `camelCase`.
That is to say, we simply adopted Java's excellent conventions and applied them to SQL.
Now, there's no way we can force you to follow this convention, even if we wished to.
Hell, you can easily write a `PhysicalNamingStrategy` which makes table and column names ALL UGLY AND SHOUTY LIKE THIS IF YOU PREFER.
But, _by default_, that's what Hibernate does, and it's frankly a pretty sane thing to do.
****
[[mapping-inheritance]]
=== Mapping entity inheritance hierarchies