Composing queries is done via "compose".
Take a look here:
https://github.com/r0man/sqlingvo/blob/master/test/sqlingvo/test/core.clj#L16
On Saturday, July 6, 2013 5:46:06 AM UTC+2, Carlo wrote:
>
> Hey Roman,
>
> The issue that I see with `sqlingvo`, and the thing which I was trying to
> solve for myself, is that it doesn't compose well. Unless I'm missing
> something, you have to generate the entire query in the one `sql` form. To
> me, this is a big restriction and was the number one thing I was trying to
> fix with `clojure-sql`.
>
> The basic sort of thing I want to be able to do is this:
>
> (def users (-> (table :users) (project [:id :person :username])))
> (def people (-> (table :people) (project [:id :first-name])))
>
> (def combined-query (-> people
> (rename {:id :person})
> (join users)
> (project [:username :first-name])))
>
> So now in queries I can use `people`, `users` and `combined-query` in the
> same way. The only difference in terms of how I can compose them is that
> they expose different fields (`users` exposes [:id, :person, :username],
> `people` exposes [:id :first-name], `combined-query` exposes [:username
> :first-name]). In this example it's not completely obvious why this would
> be beneficial, but it means that I can change `users`, for instance, to
> also have a `(select '(= :deleted false)` in its definition and no other
> code has to change. They will all join/query against the users where
> `deleted` is false without any other modifications of code.
>
> This freedom of composition is what you have in relational algebra, and
> what I was trying to get in Clojure as well. All the naming of tables and
> field aliases and everything is handled by the library, so you only have to
> worry about constructing the queries. Unfortunately SQL provides a number
> of operations outside of the relational algebra model (grouping, sorting,
> take/drop), so they've been "tacked on" as a bit of an afterthought and
> could probably use some improvement.
>
> Looking at `sqlingvo` did show up a mistake that I made in how I was
> dealing with sorts, though, so thanks for that! I think our libraries just
> have fairly different concerns at the moment.
>
> Carlo
>
>
> On 5 July 2013 20:59, r0man <roman....@burningswell.com <javascript:>>wrote:
>
>> Hi Carlo,
>>
>> if you'are looking for generating more complex SQL there's also:
>>
>> https://github.com/r0man/sqlingvo
>>
>> Roman.
>>
>> On Wednesday, July 3, 2013 10:48:07 AM UTC+2, Carlo wrote:
>>>
>>> Hey guys!
>>>
>>> I've been working on a small library to make writing SQL queries a
>>> little bit easier. It's along the same lines as ClojureQL, but takes a
>>> different approach and compiles into quite different SQL in the end.
>>>
>>> At the moment it's quite immature, but it should be able to support any
>>> queries which can be expressed in relational algebra. There will be some
>>> SQL queries which can't be expressed in clojure-sql, but hopefully there
>>> won't be too many of those. A greater limitation is that at the moment the
>>> SQL generation is specific to the PostgresSQL database (although any
>>> contributions for other databases are welcome!).
>>>
>>> Dependency vector: [clojure-sql "0.1.0"]
>>> Repository:
>>> https://bitbucket.org/czan/**clojure-sql<https://bitbucket.org/czan/clojure-sql>
>>> Clojars link:
>>> https://clojars.org/clojure-**sql<https://clojars.org/clojure-sql>
>>>
>>> Let me know what you think!
>>>
>>> Carlo
>>>
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