A playground for potential new features and nice utilities for korma.

In a leiningen project add:

[korma.incubator "0.1.1-SNAPSHOT"]

For existing features, please see https://github.com/ibdknox/Korma or http:https://sqlkorma.com/docs.

Many-to-many relationships are typically implemented using a join table that contains foreign keys that reference both tables, and these relationships are expected to be implemented in this way in Korma. In the following example, two entities, foo and bar, are defined with a many-to-many relationship between them using the join table foo_bar.

;; Entities with many-to-many relationships.
(declare foo bar)

(defentity foo
  (entity-fields :baz)
  (many-to-many bar :foo_bar
                {:lfk :foo_id
                 :rfk :bar_id}))

(defentity bar
  (entity-fields :quux)
  (many-to-many foo :foo_bar
                {:lfk :bar_id
                 :rfk :baz_id}))


;; Retrieving entities in many-to-many relationships.
(select foo
  (with bar))

The first argument to the macro, many-to-many, macro is the name of the foreign entity. The second argument is the name of the join table as a keyword. The third argument is a map containing the names of the foreign keys in the join table. The keyword, :lfk, refers to the "left-hand foreign key." That is, the column in the join table that refers to the primary key of the current entity. The keyword, :rfk, refers to the "right-hand foreign key." That is, the column in the join table that refers to the primary key of the foreign entity.

By default, Korma, returns the columns of foreign entities in has-one and belongs-to relationships as keys within the map belonging to the local entity. Sometimes, it's convenient to be able to retrieve the entity as a separate map. The macro, with-object, provides a simple way to do this.

;; Entities in a one-to-many relationship.
(declare foo bar)

(defentity foo
  (entity-fields :baz)
  (has-one bar))

(defentity bar
  (entity-fields :quux)
  (haz-one foo))

;; Retrieve an entity in a has-one relationship separately.
(select foo
  (with-object bar))

;; Retrieve an entity in a belongs-to relationship separately.
(select bar
  (with-object foo))

The entities are defined just like thay would be in any one-to-many relationship, but with-object is used instead of with in the query.

Copyright (C) 2011 Chris Granger

Distributed under the Eclipse Public License, the same as Clojure.