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Added doc to use custom datatypes re: #177 (#179)

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Colin Yates 2017-08-26 19:39:04 +01:00 committed by Michael Blume
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README.md
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@ -384,6 +384,29 @@ You can also define your own clauses:
If you do implement a clause or function handler, consider submitting a pull request so others can use it, too.
## why does my parameter get emitted as `()`?
If you want to use your own datatype as a parameter then the idiomatic approach of implementing `clojure.java.jdbc`'s [`ISQLValue`](https://clojure.github.io/java.jdbc/#clojure.java.jdbc/ISQLValue) protocol isn't enough as `honeysql` won't correct pass through your datatype, rather it will interpret it incorrectly.
To teach `honeysql` how to handle your datatype you need to implement [`honeysql.format/ToSql`](https://github.com/jkk/honeysql/blob/a9dffec632be62c961be7d9e695d0b2b85732c53/src/honeysql/format.cljc#L94). For example:
``` clojure
;; given:
(defrecord MyDateWrapper [...]
(to-sql-timestamp [this]...)
)
;; executing:
(hsql/format {:where [:> :some_column (MyDateWrapper. ...)]})
;; results in => "where :some_column > ()"
;; we can teach honeysql about it:
(extend-protocol honeysql.format.ToSql
MyDateWrapper
(to-sql [v] (to-sql (date/to-sql-timestamp v))))
;; allowing us to now:
(hsql/format {:where [:> :some_column (MyDateWrapper. ...)]})
;; which correctly results in => "where :some_column>?" and the parameter correctly set
```
## TODO
* Create table, etc.