Beyond JDBC: Exploring Diverse Solutions for Database Interactions in Clojure

• JDBC (Java Database Connectivity) is a standard Java API that allows Clojure, built on the Java Virtual Machine (JVM), to access various databases like MySQL, PostgreSQL, or Oracle.
• This method requires writing SQL queries directly in your Clojure code, similar to Java.
• While providing flexibility, it can be verbose and less aligned with Clojure's functional style.

Libraries:

• Several Clojure libraries simplify database interactions, offering abstractions over JDBC.
• Popular options include:
  • Korma: Provides a functional approach to building and executing SQL queries.
  • HikariCP: Manages database connection pools for efficient resource usage.
  • HoneySQL: Allows writing SQL queries as Clojure data structures, enhancing readability and maintainability.

Other Approaches:

• Datomic: A functional database designed for Clojure, offering unique features like immutability and temporal queries.
• In-memory databases: Libraries like Clojure Data/Cache (core.cache) offer lightweight options for storing and retrieving data temporarily within your application.

Choosing the right approach depends on factors like:

• Database type: Different libraries may specialize in specific databases.
• Project requirements: Simple data access might benefit from Korma, while complex queries might favor HoneySQL.
• Developer preference: Some developers prefer the control offered by JDBC, while others value the conciseness of libraries.

• A popular library offering an in-memory, schemaless database inspired by Datomic.
• It enables efficient querying and data manipulation with Clojure collections.

Example:

(require '[datascript :as d])

(def conn (d/create-conn nil))  ; Create an in-memory connection

(d/db conn {:name "foo" :age 30})  ; Insert data
(d/q conn [:name :age])            ; Query for all names and ages

Specter:

• A library providing a powerful DSL (Domain Specific Language) for building complex data transformations and queries.
• Useful for manipulating data from various sources, including databases.

(require '[specter :as s])

(def data [{:name "bar" :age 25} {:name "Charlie" :age 42}])

(s/select [:name (s/where :age > 30)] data)  ; Filter names with age > 30

Integrant:

• A dependency injection framework that simplifies managing database connections and other application dependencies.
• It encourages modularity and improves code organization.

(require '[integrant :as ig])

(def db-config {:dbtype "h2" :dbname "my-db"})

(def db (ig/ref (-> {:factory jdbc/get-datasource}
                      (ig/apply db-config))))

(defn get-user [user-id]
  (jdbc/query @db ["SELECT * FROM users WHERE id = ?" user-id]))