Meet Korma, a SQL DSL for Clojure

by ibdknox • 15 years ago

173 44 15 years ago

timmorgan• 15 years ago

Man this makes me want to use Clojure for something.

untog• 15 years ago

If that's all it takes, check out LINQ-to-SQL in C#- it does similar stuff. I could take or leave much of C#, but I miss LINQ every time I don't have access to it.

boyter• 15 years ago

Totally agree. LINQ to SQL is the one feature from C# I wish I had in many other languages. The power you get from the chaining and lazy loading makes implementing many complex joins and the like very easy, testable and compile time checked.

tom_b• 15 years ago

I am attracted to these types of DSLs but . . .

I work with a number of legacy data sources that often have models that are not ORM-friendly.

I fall into SQL code patterns that seem left behind by tools like this on a regular basis, particularly using SQL functions without default grouping because I'll select other stuff higher up.

A simple example:

  select
    col1,
    col2,
    some_function() over (partition by col1,col2 order by col1,col2) as some_ck
  where <some conditions>

This is often part of a larger query (e.g., this is embedded in bowels of a some longer "chain" of SQL where I will be using some_ck to decide on which tuples I want in the end).

I get pretty significant mileage out of this - meaning I write much less other code around it to handle the data.

I guess my complaint is that I often find the SQL DSLs lacking in expressiveness that I use regularly enough to miss.

Of course, this could be because I've spent too much time hacking around in legacy data in "real soon now" mode rather than in "hmm . . . let's clean up this data model" mode.

jwr• 15 years ago

I think writing DSLs for SQL makes little sense.

SQL is already a declarative query DSL, why not just use it? Putting another declarative layer on top buys you little (syntactic sugar for most libraries, this one additionally seems to deal with one-to-many relations, and I hope that support is read-write, not just read-only) — and isolates you from the database below.

In every serious application I've worked on there was a need to use something which the DSL did not support. So why do it at all?

groovy2shoes• 15 years ago

In this case, an embedded DSL brings all the goodies of Lisp's code-as-data to SQL.

technomancy• 15 years ago

Raw SQL is not very composable, while Korma emphasizes composability on the second paragraph of the page.

its2010already• 15 years ago

It does make sense to be able to define business/application logic as reusable query components.

For example, if your PERSON entity has TITLE, FIRST_NAME and LAST_NAME fields, that little bit of logic that concatenates them together in the right way to form a full name is something that is useful to define. Likewise, setting up a join of tables that is used many times in your application is something that Korma will let you do.

Even though these components may be implementable on the database side (as user defined functions or views), it may not always be possible (or desirable) to do that way.

pradocchia• 15 years ago

I spend much of my time in the database, legacy and greenfield, and I would love a better DSL than SQL, something that ran directly in the database itself and targeted the planner/optimizer rather than just emitting more SQL. I would like to be able to pass a WHERE clause to a function, or a SELECT statement to a procedure, not just simple ints, or strings to be exec'd.

zzzeek3• 15 years ago

a SQL DSL and an ORM aren't really the same thing IMHO. ORMs are about linking objects in memory to database rows, whereas the SQL DSL is just about a thin layer over the rendering of a SQL string, not unlike how you could compose a DOM object of an XML or HTML document and get a string out of it.

I'm not a Clojure user but as I have some authority on this subject I can illustrate your query as SQLAlchemy:

    select([table.c.col1, table.c.col2, 
             func.some_function().
              over(
               partition_by=[table.c.col1, table.c.col2], 
               order_by=[table.c.col1,table.c.col2])
            .label('some_ck')])
         .where(<some condition>)

msluyter2• 15 years ago

I guess I've been corrupted by working in a heavily database oriented environment, and further corrupted by the fact that it's Oracle, but for most of our own use cases, plain SQL is preferable to this. We'll probably have to run it ad hoc against the database anyway to figure out what it's doing and/or tune it. Many of our queries go into the hundreds of lines[1][2], so anything that obscures the underlying SQL itself tends to make life more difficult.

But perhaps it's just a matter of getting used to a different format.

[1] Legacy environment.

[2] Edited to add: most of our newer apps don't actually invoke huge queries from the app layer. We now tend to layer a view or pl/sql table function on top of the hairy query, so that at the app level it's mostly "select * from blah." For that simple a query, a DSL like this is probably fine, albeit, unnecessary.

moomin2• 15 years ago

Meet Korma, a SQL DSL for Clojure

Related Stories