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Further caveat on unqualified column names

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Sean Corfield 2019-11-08 11:16:17 -08:00
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doc/result-set-builders.md
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@ -15,7 +15,9 @@ The default builder for rows and result sets creates qualified keywords that mat
* `as-lower-arrays` -- table-qualified lower-case keywords,
* `as-unqualified-lower-arrays` -- simple lower-case keywords.
The reason behind the default is to a) be a simple transform, b) produce qualified keys in keeping with Clojure's direction (with `clojure.spec` etc), and c) not mess with the data. `as-arrays` is (slightly) faster than `as-maps` since it produces less data (vectors of values instead of vectors of hash maps), but the `lower` options will be slightly slower since they include (conditional) logic to convert strings to lower-case. The `unqualified` options may be slightly faster than their qualified equivalents but make no attempt to keep column names unique if your SQL joins across multiple tables.
The reason behind the default is to a) be a simple transform, b) produce qualified keys in keeping with Clojure's direction (with `clojure.spec` etc), and c) not mess with the data. `as-arrays` is (slightly) faster than `as-maps` since it produces less data (vectors of values instead of vectors of hash maps), but the `lower` options will be slightly slower since they include (conditional) logic to convert strings to lower-case. The `unqualified` options may be slightly faster than their qualified equivalents but **make no attempt to keep column names unique if your SQL joins across multiple tables**.
*Note: This is a deliberate difference from `clojure.java.jdbc` which would make column names unique by appending numeric suffices. It was always poor practice to rely on `clojure.java.jdbc`'s renaming behavior and it added quite an overhead to result set building, which is why `next.jdbc` does not support it -- use explicit column aliasing in your SQL instead if you want _unqualified_ column names!*
In addition, the following generic builders can take `:label-fn` and `:qualifier-fn` options to control how the label and qualified are processed. The `lower` variants above are implemented in terms of these, passing a `lower-case` function for both of those options.