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.