dbLoad {filehash} | R Documentation |
Load a Database
Description
Load entire database into an environment
Usage
dbLoad(db, ...)
## S4 method for signature 'filehash'
dbLoad(db, env = parent.frame(2), keys = NULL, ...)
dbLazyLoad(db, ...)
## S4 method for signature 'filehash'
dbLazyLoad(db, env = parent.frame(2), keys = NULL, ...)
db2env(db)
Arguments
db |
filehash database object |
... |
arguments passed to other methods |
env |
environment into which objects should be loaded |
keys |
specific keys to be loaded (if NULL then all keys are loaded) |
Details
dbLoad
loads objects in the database directly into the
environment specified, like load
does except with active bindings.
dbLoad
takes a second argument env
, which is an
environment, and the default for env
is parent.frame()
.
The use of makeActiveBinding
in db2env
and
dbLoad
allows for potentially large databases to, at least
conceptually, be used in R, as long as you don't need simultaneous access to
all of the elements in the database.
dbLazyLoad
loads objects in the database directly into the
environment specified, like load
does except with promises.
dbLazyLoad
takes a second argument env
, which is an
environment, and the default for env
is parent.frame()
.
With dbLazyLoad
database objects are "lazy-loaded" into
the environment. Promises to load the objects are created in the environment
specified by env
. Upon first access, those objects are copied into
the environment and will from then on reside in memory. Changes to the
database will not be reflected in the object residing in the environment
after first access. Conversely, changes to the object in the environment
will not be reflected in the database. This type of loading is useful for
read-only databases.
db2env
loads the entire database db
into an
environment via calls to makeActiveBinding
. Therefore, the data
themselves are not stored in the environment, but a function pointing to
the data in the database is stored. When an element of the environment is
accessed, the function is called to retrieve the data from the database.
If the data in the database is changed, the changes will be reflected in the
environment.
Value
dbLoad, dbLazyLoad: a character vector is returned (invisibly) containing the keys associated with the values loaded into the environment.
db2env: environment containing database keys
Methods (by class)
-
dbLoad(filehash)
: Method for filehash databases -
dbLazyLoad(filehash)
: Method for filehash databases
Functions
-
dbLazyLoad()
: Lazy load a filehash database -
db2env()
: Load active bindings into an environment and return the environment