datahike.api — io.replikativ/datahike 0.4.1474

as-of clj

(as-of db time-point)

Returns the database state at given point in time (you may use either java.util.Date or transaction ID as long).

(transact conn {:tx-data [{:db/ident :name :db/valueType :db.type/string :db/unique :db.unique/identity :db/index true :db/cardinality :db.cardinality/one} {:db/ident :age :db/valueType :db.type/long :db/cardinality :db.cardinality/one}]})

(transact conn {:tx-data [{:name "Alice" :age 25} {:name "Bob" :age 30}]})

(def date (java.util.Date.))

(transact conn {:tx-data [{:db/id [:name "Alice"] :age 35}]})

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]] :args [(as-of @conn date)]}) ; => #{["Alice" 25] ["Bob" 30]}

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]] :args [@conn]}) ; => #{["Alice" 35] ["Bob" 30]}

connect clj

(connect)

(connect config)

Connects to a datahike database via configuration map. For more information on the configuration refer to the docs.

The configuration for a connection is a subset of the Datahike configuration with only the store necessary: :store.

:store defines the backend configuration as hash-map with mandatory key: :backend and store dependent keys.

Per default Datahike ships with :mem and :file backend.

The default configuration: {:store {:backend :mem :id "default"}}

Usage:

Connect to default in-memory configuration: (connect)

Connect to a database with persistent store: (connect {:store {:backend :file :path "/tmp/example"}})

create-database clj

(create-database)

(create-database config & deprecated-opts)

Creates a database via configuration map. For more information on the configuration refer to the docs.

The configuration is a hash-map with keys: :store, :initial-tx, :keep-history?, :schema-flexibility, :index

• :store defines the backend configuration as hash-map with mandatory key: :backend and store dependent keys. Per default Datahike ships with :mem and :file backend.
• :initial-tx defines the first transaction into the database, often setting default data like the schema.
• :keep-history? is a boolean that toggles whether Datahike keeps historical data.
• :schema-flexibility can be set to either :read or :write setting the validation method for the data.
  • :read validates the data when your read data from the database, :write validates the data when you transact new data.
• :index defines the data type of the index. Available are :datahike.index/hitchhiker-tree, :datahike.index/persistent-set (only available with in-memory storage)
• :name defines your database name optionally, if not set, a random name is created
• :transactor optionally configures a transactor as a hash map. If not set, the default local transactor is used.

Default configuration has in-memory store, keeps history with write schema flexibility, and has no initial transaction: {:store {:backend :mem :id "default"} :keep-history? true :schema-flexibility :write}

Usage:

;; create an empty database:
(create-database {:store {:backend :mem :id "example"} :name "my-favourite-database"})

;; Datahike has a strict schema validation (schema-flexibility `:write`) policy by default, that only allows transaction of data that has been pre-defined by a schema.
;; You may influence this behaviour using the `:schema-flexibility` attribute:
(create-database {:store {:backend :mem :id "example"} :schema-flexibility :read})

;; By storing historical data in a separate index, datahike has the capability of querying data from any point in time.
;; You may control this feature using the `:keep-history?` attribute:
(create-database {:store {:backend :mem :id "example"} :keep-history? false})

;; Initial data after creation may be added using the `:initial-tx` attribute, which in this example adds a schema:
(create-database {:store {:backend :mem :id "example"} :initial-tx [{:db/ident :name :db/valueType :db.type/string :db.cardinality/one}]})

database-exists? clj

(database-exists? config)

Checks if a database exists via configuration map. Usage:

(database-exists? {:store {:backend :mem :id "example"}})

datoms clj multimethod

(datoms db arg-map)

(datoms db index & components)

Index lookup. Returns a sequence of datoms (lazy iterator over actual DB index) which components (e, a, v) match passed arguments. Datoms are sorted in index sort order. Possible index values are: :eavt, :aevt, :avet.

Accepts db and a map as arguments with the keys :index and :components provided within the map, or the arguments provided separately.

Usage:

Set up your database. Beware that for the :avet index the index needs to be set to true for the attribute :likes.

(d/transact db [{:db/ident :name
                 :db/type :db.type/string
                 :db/cardinality :db.cardinality/one}
                {:db/ident :likes
                 :db/type :db.type/string
                 :db/index true
                 :db/cardinality :db.cardinality/many}
                {:db/ident :friends
                 :db/type :db.type/ref
                 :db/cardinality :db.cardinality/many}]

(d/transact db [{:db/id 4 :name "Ivan"
                {:db/id 4 :likes "fries"
                {:db/id 4 :likes "pizza"}
                {:db/id 4 :friends 5}])

(d/transact db [{:db/id 5 :name "Oleg"}
                {:db/id 5 :likes "candy"}
                {:db/id 5 :likes "pie"}
                {:db/id 5 :likes "pizza"}])

Find all datoms for entity id == 1 (any attrs and values) sort by attribute, then value

(datoms @db {:index :eavt
             :components [1]}) ; => (#datahike/Datom [1 :friends 2]
                               ;     #datahike/Datom [1 :likes "fries"]
                               ;     #datahike/Datom [1 :likes "pizza"]
                               ;     #datahike/Datom [1 :name "Ivan"])

Find all datoms for entity id == 1 and attribute == :likes (any values) sorted by value

(datoms @db {:index :eavt
             :components [1 :likes]}) ; => (#datahike/Datom [1 :likes "fries"]
                                      ;     #datahike/Datom [1 :likes "pizza"])

Find all datoms for entity id == 1, attribute == :likes and value == "pizza"

(datoms @db {:index :eavt
             :components [1 :likes "pizza"]}) ; => (#datahike/Datom [1 :likes "pizza"])

Find all datoms for attribute == :likes (any entity ids and values) sorted by entity id, then value

(datoms @db {:index :aevt
             :components [:likes]}) ; => (#datahike/Datom [1 :likes "fries"]
                                    ;     #datahike/Datom [1 :likes "pizza"]
                                    ;     #datahike/Datom [2 :likes "candy"]
                                    ;     #datahike/Datom [2 :likes "pie"]
                                    ;     #datahike/Datom [2 :likes "pizza"])

Find all datoms that have attribute == :likes and value == "pizza" (any entity id) :likes must be a unique attr, reference or marked as :db/index true

(datoms @db {:index :avet
             :components [:likes "pizza"]}) ; => (#datahike/Datom [1 :likes "pizza"]
                                              ;     #datahike/Datom [2 :likes "pizza"])

Find all datoms sorted by entity id, then attribute, then value

(datoms @db {:index :eavt}) ; => (...)

Useful patterns:

Get all values of :db.cardinality/many attribute

(->> (datoms @db {:index :eavt
                  :components [eid attr]})
     (map :v))

Lookup entity ids by attribute value

(->> (datoms @db {:index :avet
                  :components [attr value]})
     (map :e))

Find all entities with a specific attribute

(->> (datoms @db {:index :aevt
                  :components [attr]})
     (map :e))

Find “singleton” entity by its attr

(->> (datoms @db {:index :aevt
                  :components [attr]})
     first
     :e)

Find N entities with lowest attr value (e.g. 10 earliest posts)

(->> (datoms @db {:index :avet
                  :components [attr]})
     (take N))

Find N entities with highest attr value (e.g. 10 latest posts)

(->> (datoms @db {:index :avet
                  :components [attr]})
     (reverse)
     (take N))

Gotchas:

• Index lookup is usually more efficient than doing a query with a single clause.
• Resulting iterator is calculated in constant time and small constant memory overhead.
• Iterator supports efficient first, next, reverse, seq and is itself a sequence.
• Will not return datoms that are not part of the index (e.g. attributes with no :db/index in schema when querying :avet index).
  • :eavt and :aevt contain all datoms.
  • :avet only contains datoms for references, :db/unique and :db/index attributes.

db clj

(db conn)

Returns the underlying immutable database value from a connection.

Exists for Datomic API compatibility. Prefer using @conn directly if possible.

db-with clj

(db-with db tx-data)

Applies transaction to an immutable db value, returning new immutable db value. Same as (:db-after (with db tx-data)).

delete-database clj

(delete-database config)

Deletes a database given via configuration map. Storage configuration :store is mandatory. For more information refer to the docs

entity clj

(entity db eid)

Retrieves an entity by its id from database. Entities are lazy map-like structures to navigate Datahike database content.

For eid pass entity id or lookup attr:

(entity db 1)
(entity db [:unique-attr :value])

If entity does not exist, nil is returned:

(entity db -1) ; => nil

Creating an entity by id is very cheap, almost no-op, as attr access is on-demand:

(entity db 1) ; => {:db/id 1}

Entity attributes can be lazily accessed through key lookups:

(:attr (entity db 1)) ; => :value
(get (entity db 1) :attr) ; => :value

Cardinality many attributes are returned sequences:

(:attrs (entity db 1)) ; => [:v1 :v2 :v3]

Reference attributes are returned as another entities:

(:ref (entity db 1)) ; => {:db/id 2}
(:ns/ref (entity db 1)) ; => {:db/id 2}

References can be walked backwards by prepending _ to name part of an attribute:

(:_ref (entity db 2)) ; => [{:db/id 1}]
(:ns/_ref (entity db 2)) ; => [{:db/id 1}]

Reverse reference lookup returns sequence of entities unless attribute is marked as :db/component:

(:_component-ref (entity db 2)) ; => {:db/id 1}

Entity gotchas:

• Entities print as map, but are not exactly maps (they have compatible get interface though).
• Entities are effectively immutable “views” into a particular version of a database.
• Entities retain reference to the whole database.
• You can’t change database through entities, only read.
• Creating an entity by id is very cheap, almost no-op (attributes are looked up on demand).
• Comparing entities just compares their ids. Be careful when comparing entities taken from differenct dbs or from different versions of the same db.
• Accessed entity attributes are cached on entity itself (except backward references).
• When printing, only cached attributes (the ones you have accessed before) are printed. See [[touch]].

entity-db clj

(entity-db entity)

Returns a db that entity was created from.

filter clj

(filter db pred)

Returns a view over database that has same interface but only includes datoms for which the (pred db datom) is true. Can be applied multiple times.

Filtered DB gotchas:

• All operations on filtered database are proxied to original DB, then filter pred is applied.
• Not cached. You pay filter penalty every time.
• Supports entities, pull, queries, index access.
• Does not support hashing of DB.
• Does not support with and db-with.

history clj

(history db)

Returns the full historical state of the database you may interact with.

(transact conn {:tx-data [{:db/ident :name :db/valueType :db.type/string :db/unique :db.unique/identity :db/index true :db/cardinality :db.cardinality/one} {:db/ident :age :db/valueType :db.type/long :db/cardinality :db.cardinality/one}]})

(transact conn {:tx-data [{:name "Alice" :age 25} {:name "Bob" :age 30}]})

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]] :args [(history @conn)]}) ; => #{["Alice" 25] ["Bob" 30]}

(transact conn {:tx-data [{:db/id [:name "Alice"] :age 35}]})

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]] :args [@conn]}) ; => #{["Alice" 35] ["Bob" 30]}

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]] :args [(history @conn)]}) ; => #{["Alice" 25] ["Bob" 30]}

index-range clj

(index-range db arg-map)

Returns part of :avet index between [_ attr start] and [_ attr end] in AVET sort order.

Same properties as datoms.

attr must be a reference, unique attribute or marked as :db/index true.

Usage:

(transact db {:tx-data [{:db/ident :name
                         :db/type :db.type/string
                         :db/cardinality :db.cardinality/one}
                        {:db/ident :likes
                         :db/index true
                         :db/type :db.type/string
                         :db/cardinality :db.cardinality/many}
                        {:db/ident :age
                         :db/unique :db.unique/identity
                         :db/type :db.type/ref
                         :db/cardinality :db.cardinality/many}]})

(transact db {:tx-data [{:name "Ivan"}
                        {:age 19}
                        {:likes "fries"}
                        {:likes "pizza"}
                        {:likes "candy"}
                        {:likes "pie"}
                        {:likes "pizza"}]})

(index-range db {:attrid :likes
                 :start  "a"
                 :end    "zzzzzzzzz"}) ; => '(#datahike/Datom [2 :likes "candy"]
                                         ;      #datahike/Datom [1 :likes "fries"]
                                         ;      #datahike/Datom [2 :likes "pie"]
                                         ;      #datahike/Datom [1 :likes "pizza"]
                                         ;      #datahike/Datom [2 :likes "pizza"])

(index-range db {:attrid :likes
                 :start  "egg"
                 :end    "pineapple"}) ; => '(#datahike/Datom [1 :likes "fries"]
                                         ;      #datahike/Datom [2 :likes "pie"])

Useful patterns:

; find all entities with age in a specific range (inclusive)
(->> (index-range db {:attrid :age :start 18 :end 60}) (map :e))

is-filtered clj

(is-filtered x)

Returns true if this database was filtered using filter, false otherwise.

listen clj

(listen conn callback)

(listen conn key callback)

Listen for changes on the given connection. Whenever a transaction is applied to the database via transact, the callback is called with the transaction report. key is any opaque unique value.

Idempotent. Calling listen with the same twice will override old callback with the new value.

Returns the key under which this listener is registered. See also unlisten.

load-entities clj

(load-entities conn tx-data)

Load entities directly

pull clj

(pull db arg-map)

(pull db selector eid)

Fetches data from database using recursive declarative description. See docs.datomic.com/on-prem/pull.html.

Unlike entity, returns plain Clojure map (not lazy).

Usage:

(pull db [:db/id, :name, :likes, {:friends [:db/id :name]}] 1) ; => {:db/id   1,
                                                                     :name    "Ivan"
                                                                     :likes   [:pizza]
                                                                     :friends [{:db/id 2, :name "Oleg"}]}

The arity-2 version takes :selector and :eid in arg-map.

pull-many clj

(pull-many db selector eids)

Same as pull, but accepts sequence of ids and returns sequence of maps.

Usage:

(pull-many db [:db/id :name] [1 2]) ; => [{:db/id 1, :name "Ivan"}
                                          {:db/id 2, :name "Oleg"}]

q clj multimethod

(q arg-map)

(q query & args)

Executes a datalog query. See docs.datomic.com/on-prem/query.html.

Usage:

Query as parameter with additional args:

(q '[:find ?value
     :where [_ :likes ?value]]
   #{[1 :likes "fries"]
     [2 :likes "candy"]
     [3 :likes "pie"]
     [4 :likes "pizza"]}) ; => #{["fries"] ["candy"] ["pie"] ["pizza"]}

Or query passed in arg-map:

(q {:query '[:find ?value
             :where [_ :likes ?value]]
    :offset 2
    :limit 1
    :args [#{[1 :likes "fries"]
             [2 :likes "candy"]
             [3 :likes "pie"]
             [4 :likes "pizza"]}]}) ; => #{["fries"] ["candy"] ["pie"] ["pizza"]}

Or query passed as map of vectors:

(q '{:find [?value] :where [[_ :likes ?value]]}
   #{[1 :likes "fries"]
     [2 :likes "candy"]
     [3 :likes "pie"]
     [4 :likes "pizza"]}) ; => #{["fries"] ["candy"] ["pie"] ["pizza"]}

Or query passed as string:

(q {:query "[:find ?value :where [_ :likes ?value]]"
    :args [#{[1 :likes "fries"]
             [2 :likes "candy"]
             [3 :likes "pie"]
             [4 :likes "pizza"]}]})

Query passed as map needs vectors as values. Query can not be passed as list. The 1-arity function takes a map with the arguments :query and :args and optionally the additional keys :offset and :limit.

release clj

(release conn)

Releases a database connection

reverse-schema clj

(reverse-schema db)

Returns current reverse schema definition.

schema clj

(schema db)

Returns current schema definition.

seek-datoms clj multimethod

(seek-datoms db arg-map)

(seek-datoms db index & components)

Similar to datoms, but will return datoms starting from specified components and including rest of the database until the end of the index.

If no datom matches passed arguments exactly, iterator will start from first datom that could be considered “greater” in index order.

Usage:

(seek-datoms @db {:index :eavt
                  :components [1]}) ; => (#datahike/Datom [1 :friends 2]
                                    ;     #datahike/Datom [1 :likes "fries"]
                                    ;     #datahike/Datom [1 :likes "pizza"]
                                    ;     #datahike/Datom [1 :name "Ivan"]
                                    ;     #datahike/Datom [2 :likes "candy"]
                                    ;     #datahike/Datom [2 :likes "pie"]
                                    ;     #datahike/Datom [2 :likes "pizza"])

(seek-datoms @db {:index :eavt
                  :components [1 :name]}) ; => (#datahike/Datom [1 :name "Ivan"]
                                          ;     #datahike/Datom [2 :likes "candy"]
                                          ;     #datahike/Datom [2 :likes "pie"]
                                          ;     #datahike/Datom [2 :likes "pizza"])

(seek-datoms @db {:index :eavt
                  :components [2]}) ; => (#datahike/Datom [2 :likes "candy"]
                                    ;     #datahike/Datom [2 :likes "pie"]
                                    ;     #datahike/Datom [2 :likes "pizza"])

No datom [2 :likes "fish"], so starts with one immediately following such in index

(seek-datoms @db {:index :eavt
                  :components [2 :likes "fish"]}) ; => (#datahike/Datom [2 :likes "pie"]
                                                    ;     #datahike/Datom [2 :likes "pizza"])

since clj

(since db time-point)

Returns the database state since a given point in time (you may use either java.util.Date or a transaction ID as long). Be aware: the database contains only the datoms that were added since the date.

(transact conn {:tx-data [{:db/ident :name
                           :db/valueType :db.type/string
                           :db/unique :db.unique/identity
                           :db/index true
                           :db/cardinality :db.cardinality/one}
                          {:db/ident :age
                           :db/valueType :db.type/long
                           :db/cardinality :db.cardinality/one}]})

(transact conn {:tx-data [{:name "Alice" :age 25} {:name "Bob" :age 30}]})

(def date (java.util.Date.))

(transact conn [{:db/id [:name "Alice"] :age 30}])

(q '[:find ?n ?a
     :in $ $since
     :where
     [$ ?e :name ?n]
     [$since ?e :age ?a]]
     @conn
     (since @conn date)) ; => #{["Alice" 30]}

(q {:query '[:find ?n ?a :where [?e :name ?n] [?e :age ?a]]
    :args [@conn]}) ; => #{["Alice" 30] ["Bob" 30]}

tempid clj

(tempid part)

(tempid part x)

Allocates and returns a unique temporary id (a negative integer). Ignores part. Returns x if it is specified.

Exists for Datomic API compatibility. Prefer using negative integers directly if possible.

transact clj

(transact conn arg-map)

Applies transaction to the underlying database value and atomically updates the connection reference to point to the result of that transaction, the new db value.

Accepts the connection and a map or a vector as argument, specifying the transaction data.

Returns transaction report, a map:

{:db-before ...       ; db value before transaction
 :db-after  ...       ; db value after transaction
 :tx-data   [...]     ; plain datoms that were added/retracted from db-before
 :tempids   {...}     ; map of tempid from tx-data => assigned entid in db-after
 :tx-meta   tx-meta } ; the exact value you passed as `tx-meta`

Note! conn will be updated in-place and is not returned from transact.

Usage:

;; add a single datom to an existing entity (1)
(transact conn [[:db/add 1 :name "Ivan"]])

;; retract a single datom
(transact conn [[:db/retract 1 :name "Ivan"]])

;; retract single entity attribute
(transact conn [[:db.fn/retractAttribute 1 :name]])

;; retract all entity attributes (effectively deletes entity)
(transact conn [[:db.fn/retractEntity 1]])

;; create a new entity (`-1`, as any other negative value, is a tempid
;; that will be replaced by Datahike with the next unused eid)
(transact conn [[:db/add -1 :name "Ivan"]])

;; check assigned id (here `*1` is a result returned from previous `transact` call)
(def report *1)
(:tempids report) ; => {-1 296, :db/current-tx 536870913}

;; check actual datoms inserted
(:tx-data report) ; => [#datahike/Datom [296 :name "Ivan" 536870913]]

;; tempid can also be a string
(transact conn [[:db/add "ivan" :name "Ivan"]])
(:tempids *1) ; => {"ivan" 5, :db/current-tx 536870920}

;; reference another entity (must exist)
(transact conn [[:db/add -1 :friend 296]])

;; create an entity and set multiple attributes (in a single transaction
;; equal tempids will be replaced with the same unused yet entid)
(transact conn [[:db/add -1 :name "Ivan"]
                [:db/add -1 :likes "fries"]
                [:db/add -1 :likes "pizza"]
                [:db/add -1 :friend 296]])

;; create an entity and set multiple attributes (alternative map form)
(transact conn [{:db/id  -1
                 :name   "Ivan"
                 :likes  ["fries" "pizza"]
                 :friend 296}])

;; update an entity (alternative map form). Can’t retract attributes in
;; map form. For cardinality many attrs, value (fish in this example)
;; will be added to the list of existing values
(transact conn [{:db/id  296
                 :name   "Oleg"
                 :likes  ["fish"]}])

;; ref attributes can be specified as nested map, that will create a nested entity as well
(transact conn [{:db/id  -1
                 :name   "Oleg"
                 :friend {:db/id -2
                 :name "Sergey"}}])

;; schema is needed for using a reverse attribute
(is (transact conn [{:db/valueType :db.type/ref
                     :db/cardinality :db.cardinality/one
                     :db/ident :friend}]))

;; reverse attribute name can be used if you want a created entity to become
;; a value in another entity reference
(transact conn [{:db/id  -1
                 :name   "Oleg"
                 :_friend 296}])
;; equivalent to
(transact conn [[:db/add  -1 :name   "Oleg"]
                {:db/add 296 :friend -1]])

unlisten clj

(unlisten conn key)

Removes registered listener from connection. See also listen.

with clj

(with db arg-map)

Same as transact`, but applies to an immutable database value. Returns transaction report (see transact).

Accepts tx-data and tx-meta as a map.

(with @conn {:tx-data [[:db/add 1 :name "Ivan"]]}) ; => {:db-before #datahike/DB {:max-tx 536870912 :max-eid 0},
                                                     ;     :db-after #datahike/DB {:max-tx 536870913 :max-eid 1},
                                                     ;     :tx-data [#datahike/Datom [1 :name "Ivan" 536870913]],
                                                     ;     :tempids #:db{:current-tx 536870913},
                                                     ;     :tx-meta nil}

(with @conn {:tx-data [[:db/add 1 :name "Ivan"]]
             :tx-meta {:foo :bar}}) ; => {:db-before #datahike/DB {:max-tx 536870912 :max-eid 0},
                                    ;     :db-after #datahike/DB {:max-tx 536870913 :max-eid 1},
                                    ;     :tx-data [#datahike/Datom [1 :name "Ivan" 536870913]],
                                    ;     :tempids #:db{:current-tx 536870913},
                                    ;     :tx-meta {:foo :bar}}