Supported Operations
Datomic provides the following set of operations:
- database operations
- ACID transactions
- dynamic schema
- Datalog query and pull
- time operations
- raw index access
- deploy entire applications to Datomic with ions
- SQL analytics support
Database Operations
The Datomic API allows you to create, list, and delete databases. For more information, see the Client API.
ACID Transactions
Databases are accumulate-only, and all new information is added by fully
serialized ACID transactions. The transact
operation takes as its
arguments
- a connection to a database
- a collection that can include raw assertions, raw retractions, and transaction functions for conditional operations.
For example, to increase an item's price by 10%, you would pass a
transaction function to transact
, and two new datoms would be added to
the database:
- a retraction of the previous price
- an assertion of the new price
For more information, see transactions.
Installing Schema
Schema attributes are ordinary entities in a database, and are added via ACID transactions just like any other data. Schema attributes must be defined in a transaction prior to any transaction that uses them.
For more information, see schema.
Query: Datalog and Pull
The query
operation provides access to Datomic Datalog, a powerful
deductive query system. Datomic Datalog includes unification, joins,
predicates, functions, conjunction, disjunction, negation, and reusable
rules.
The pull
operation is a declarative way to make hierarchical (or
nested) selections of information about entities. pull
is
integrated in query
and also available as a standalone API.
For more information, see query.
Time
Datomic is accumulate-only, remembering the history of all information.
The db
operation returns the current value of a database. This value
can then be filtered:
- the
as-of
operation filters a database back to a past point in time - the
since
operation filters a database to include only datoms after a point in time - the
history
operations returns an unfiltered view of all present and past information.
Datomic transactions are reified, that is, transactions are themselves
entities in a database. You can use query
and pull
to retrieve
information about transactions associated with an entity. Or you can go
in the opposite direction, retrieving datoms from transactions directly
via the tx-range
operation.
For more information, see time.
Raw Indexes
Datomic provides direct iteration on indexes. Most applications will not
use this, and you should prefer instead the higher-level query
and
pull
operations.
The datoms
operation can seek to a point in any index and iterate from
there, and the index-range
operation can provide a value range from the
AVET index.
For more information, see indexes.