Connect to a Database

Setup your project or run the included REPL. If you wish to persist your changes to disk then run a transactor and use the transactor's database URI below.

Include the Peer API:

(require '[datomic.api :as d])

=>
nil

Create the URI that allows you to create and connect to a database.

An in-memory database URI will have three parts:

• datomic:, identifying it as a Datomic URI
• mem://, the mem storage protocol that uses local memory instead of a persistent store
• hello, the name of the database

If you ran a transactor to use local storage then supply the database uri that was supplied when you passed the -Ddatomic.printConnectionInfo=true flag. Replace <DB_NAME> with the name of the database that you want to create:

Bind a var, db-uri, to the value of the URI:

(def db-uri "datomic:mem://hello")

;; If you're using local dev storage, use the db uri you created earlier.
;; replace <DB-NAME> with your database name. It will look similar to:
;; (def db-uri "datomic:dev://localhost:4334/hello")

=>
#'user/db-uri

Create the "hello" database using the create-database function:

(d/create-database db-uri)

=>
true

Once you have created a database, you can use the Datomic Peer Library to interact with it.

Connect to the transactor in the same REPL that you used to create your database:

(def conn (d/connect db-uri))

=>
#'user/conn

You should see that a var was created called conn which is holding your database connection. You can inspect it:

conn

=> #object[datomic.peer.LocalConnection 0x6ca372ef "datomic.peer.LocalConnection@6ca372ef"]

Any transactions submitted to the connection will be persisted to the storage that you chose when creating your database.

Try adding a new entity with the :db/doc value "Hello world".

@(d/transact conn [{:db/doc "Hello world"}])

=>
{:db-before datomic.db.Db@33e08f8b, :db-after datomic.db.Db@7957bcc8, :tx-data [#datom[13194139534312 50 #inst "2022-03-18T09:33:18.156-00:00" 13194139534312 true] #datom[17592186045417 62 "Hello world" 13194139534312 true]], :tempids {-9223301668109598134 17592186045417}}

The next step will be to define some schema for your new database.