Packages

t

molecule.core.generic

GenericVAET

trait GenericVAET extends AnyRef

VAET reverse Index.

"The VAET index contains all and only datoms whose attribute has a :db/valueType of :db.type/ref. This is also known as the reverse index, since it allows efficient navigation of relationships in reverse." (from Datomic documentation)

Access the VAET Index in Molecule by instantiating a VAET object with one or more arguments and then add generic attributes:

for {
  // Say we have 3 entities pointing to one entity:
  _ <- Release.e.name.Artists.e.name.get.map(_ ==> List(
    (r1, "Abbey Road", a1, "The Beatles"),
    (r2, "Magical Mystery Tour", a1, "The Beatles"),
    (r3, "Let it be", a1, "The Beatles"),
  ))

  // .. then we can get the reverse relationships with the VAET Index:
  _ <- VAET(a1).v.a.e.get.map(_ ==> List(
    (a1, ":Release/artists", r1),
    (a1, ":Release/artists", r2),
    (a1, ":Release/artists", r3),
  ))

  // Narrow search with multiple arguments
  _ <- VAET(a1, ":Release/artist").e.get.map(_ ==> List(r1, r2, r3))
  _ <- VAET(a1, ":Release/artist", r2).e.get.map(_ ==> List(r2))
  _ <- VAET(a1, ":Release/artist", r2, t7).e.get.map(_ ==> List(r2))
} yield ()

Index attributes available:

  • e - Entity id (Long)
  • a - Full attribute name like ":Person/name" (String)
  • v - Value of Datoms (Any)
  • t - Transaction pointer (Long/Int)
  • tx - Transaction entity id (Long)
  • txInstant - Transaction wall clock time (java.util.Date)
  • op - Operation status: assertion (true) / retraction (false)
Source
GenericVAET.scala
Note

The Molecule Index API's don't allow returning the whole Index/the whole database. So omitting arguments constructing the Index object (like VAET.v.a.e.t.get) will throw an exception.
Please use Datomics API if you need to return the whole database Index:
conn.db.datoms(datomic.Database.VAET)

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  20. object VAET extends VAET_0_0_L0[VAET_, Init] with FirstNS

    VAET Index object to start VAET reverse Index molecule.

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