Connect to a Database

• To begin, launch a REPL from the root directory of the Datomic folder using the bin/repl script:

bin/repl

• Require the Peer API:

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

=>
nil

The Datomic Peer API names databases with a URI that includes the protocol name, storage connection information, and a database name. The complete URI for a database named "hello" on the transactor you started in the previous step is "datomic:dev://localhost:4334/hello".

• Def a var, db-uri, with this name:

(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 will see that a var was created called conn which is holding your database connection. To inspect it, run:

conn

=> #object[datomic.peer.Connection
        0x10a59519
        "{:unsent-updates-queue 0, :pending-txes 0, :next-t 1005, :basis-t 1001, :index-rev 0, :db-id \"hello-c33c1487-877a-404a-88d0-0aac99518598\"}"]

Any transactions submitted to the connection will be persisted in 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@e438f2c9,
 :db-after datomic.db.Db@5d0a1343,
 :tx-data [#datom[13194139534317 50 #inst"2024-05-13T00:52:21.776-00:00" 13194139534317 true]
           #datom[17592186045422 62 "Hello world" 13194139534317 true]],
 :tempids {-9223300668110598143 17592186045422}}

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