| Title: | Provides Access to Databases Through the JDBC Interface |
|---|---|
| Description: | The RJDBC package is an implementation of R's DBI interface using JDBC as a back-end. This allows R to connect to any DBMS that has a JDBC driver. |
| Authors: | Simon Urbanek <[email protected]> |
| Maintainer: | Simon Urbanek <[email protected]> |
| License: | MIT + file LICENSE |
| Version: | 0.2-10 |
| Built: | 2024-11-05 06:27:18 UTC |
| Source: | CRAN |
JDBC creates a new DBI driver that can be used to start JDBC
connections.
findDrivers attempts to find and load all JDBC 4 drivers on the
class path.
JDBC (driverClass = "", classPath = "", identifier.quote = NA) findDrivers(classPath = "", service = "java.sql.Driver", loader = NULL)JDBC (driverClass = "", classPath = "", identifier.quote = NA) findDrivers(classPath = "", service = "java.sql.Driver", loader = NULL)
driverClass |
name of the Java class of the JDBC driver to
load or a one of Java driver instances from |
classPath |
character vector, class path that needs to be appended in order to load the desired JDBC driver. Usually it is the path to the JAR file containing the driver and all necessary dependencies. It can be a vector and all paths are expanded. |
identifier.quote |
character to use for quoting identifiers in
automatically generated SQL statements or |
service |
string, name of the services class (for JDBC always "java.sql.Driver") |
loader |
Java class loader to use during the look-up or
|
JDBC function has two purposes. One is to initialize the Java VM
and load a Java JDBC driver (not to be confused with the
JDBCDriver R object which is actually a DBI driver). The
second purpose is to create a proxy R object which can be used to a
call dbConnect which actually creates a connection.
JDBC requires a JDBC driver for a database-backend to be
loaded. Usually a JDBC driver is supplied in a Java Archive (jar)
file. The path to such a file can be specified in
classPath. The driver itself has a Java class name that is used
to load the driver (for example the MySQL driver uses
com.mysql.jdbc.Driver), this has to be specified in
driverClass.
Modern drivers (those supporting JDBC 4) may use Java Service Provider
interface for discovery and those can be found using the
findDrivers() function which returns a list of drivers. You
can pass any of the returned elements as classDriver. Note that
the discovery is dynamic, so you can use
rJava::.jaddClassPath(...) to add new locations in which Java
will look for driver JAR files. However, only drivers providing JSP
metadata in their JAR files can be found. JSP was introduced in Java
1.6 so findDrivers() only works on Java 1.6 or higher.
There are currently three different ways to specify drivers:
dbConnect(JDBC("my.Driver.Class", "driver.jar"), ...)
is the most explicit way where the specified driver class is used
and expected to be found on the class path. This always works, but
the user has to know the full name of the driver class.
dbConnect(JDBC(, "driver.jar"), ...) omits the driver
class which means JDBC will try to find the driver using the
DriverManager. This only works if the JVM has been
loaded with the driver when initialized, so this method is
discouraged as it is in general very unreliable. The
DriverManager never updates the list of drivers, so once your
driver is not found, there is nothing you can do about it.
dbConnect(JDBC(findDrivers("driver.jar")[[1]]), ...) uses
findDrivers() (see details above) to find all available
drivers and then passes the needed driver (in this example the first
one) to JDBC(). You don't need to repeat teh class path in
this case as it is already set by findDrivers(). It is best
to look at the output to see which drivers have been found, but if
you pass the list, the first driver is used. Note that if you print
the driver you will see the class name so you can also use this
information in the first method above instead.
If you have issues loading your driver (e.g., you get ClassNotFound
errors), make sure you specify all dependencies of your driver,
not just the main JAR file. They all must be listed on the
class path. Also make sure your JVM is supported by the driver, trying
to load drivers with too old JVM versions also leads to ClassNotFound
errors (as the loader will ignore calsses it cannot load). You can
always enable debugging information in the rJava class loader using
.jclassLoader()$setDebug(1L) for more verbose output that may
help in your troubleshooting.
Due to the fact that JDBC can talk to a wide variety of databases, the
SQL dialect understood by the database is not known in
advance. Therefore the RJDBC implementation tries to adhere to the SQL92
standard, but not all databases are compliant. This affects mainly
functions such as dbWriteTable that have to
automatically generate SQL code. One major ability is the support for
quoted identifiers. The SQL92 standard uses double-quotes, but many
database engines either don't support it or use other character. The
identifier.quote parameter allows you to set the proper quote
character for the database used. For example MySQL would require
identifier.quote="`". If set to NA, the ability to quote
identifiers is disabled, which poses restrictions on the names that
can be used for tables and fields. Other functionality is not affected.
As of RDJBC 0.2-2 JDBC-specific stored procedure calls starting with
{call and {?= call are supported in the statements.
JDBC returns a JDBCDriver object that can be used in
calls to dbConnect.
findDrivers returns a list of Java object references to
instances of JDBC drivers that were found. The list can be empty if no
drivers were found. Elements can be used as the driverClass in
calls to JDBC.
## Not run: drv <- JDBC("com.mysql.jdbc.Driver", "/etc/jdbc/mysql-connector-java-3.1.14-bin.jar", "`") conn <- dbConnect(drv, "jdbc:mysql://localhost/test") dbListTables(conn) data(iris) dbWriteTable(conn, "iris", iris) dbGetQuery(conn, "select count(*) from iris") d <- dbReadTable(conn, "iris") ## End(Not run)## Not run: drv <- JDBC("com.mysql.jdbc.Driver", "/etc/jdbc/mysql-connector-java-3.1.14-bin.jar", "`") conn <- dbConnect(drv, "jdbc:mysql://localhost/test") dbListTables(conn) data(iris) dbWriteTable(conn, "iris", iris) dbGetQuery(conn, "select count(*) from iris") d <- dbReadTable(conn, "iris") ## End(Not run)
Class representing a (DBI) database connection which uses JDBC to connect to a database.
Objects can be created by call to dbConnect of a
JDBC driver.
jc:Java object representing the connection.
identifier.quote:Quote character to use for
quoting identifiers it automatically generated SQL
statements or NA if the back-end doesn't support
quoted identifiers. Usually the value is inherited from the
"JDBCDriver".
Class "DBIConnection-class", directly.
Class "DBIObject-class", by class "DBIConnection", distance 2.
No methods defined with class "JDBCConnection" in the signature.
JDBC, "JDBCDriver"
Methods for the class ‘JDBCConnection’ in Package ‘RJDBC’.
dbSendQuery and dbSendUpdate submit a SQL query to the
database. The difference between the two is only that
dbSendUpdate is used with DBML queries and thus doesn't return
any result set.
dbGetTables and dbGetFields are similar to
dbListTables and dbListFields but the result is a data
frame with all available details (whereas the latter return only a
character vector of the names).
dbSendUpdate (conn, statement, ...) dbGetTables (conn, ...) dbGetFields (conn, ...)dbSendUpdate (conn, statement, ...) dbGetTables (conn, ...) dbGetFields (conn, ...)
conn |
connection object |
statement |
SQL statement to execute |
... |
additional arguments to prepared statement substituted for "?" |
Some notable enhancements to the DBI API:
dbSendUpdate supports vectorized arguments which is far more
efficient than using scalar updates. Example:
dbSendUpdate(c, "INSERT INTO myTable VALUES(?, ?)", rnorm(1000), runif(1000))
performs a single JDBC batchExecute() call. Additional
parameter max.batch=10000L is an integer that specifies the
maximum batch size supported by the DBMS.
dbSendQuery and dbSendUpdate accept both ...
(populated frist) as well as list= (populated as second).
Only unnamed arguments are used from ... (assuming that those
are function arguments and no data) while all elements are used from
list=.
dbGetQuery is a shorthand for sendQuery +
fetch. Parameters n=-1, block=2048L and
use.label=TRUE are passed through to fetch() others to
dbSendQuery.
dbListTables and dbGetTables have the arguments
(conn, pattern="%", schema=NULL). dbExistsTable is just
a wrapper for dbGetTables.
dbWriteTable is defined as
(conn, name, value, overwrite=FALSE, append=FALSE, force=FALSE, ..., max.batch=10000L)
and is just a short-hand for the corresponding dbSendUpdate()
statements. Since it is only a convenience wrapper, it is strongly
recommended to use dbSendUpdate() in any real use-cases
as you have far more control over the shape and properties of the
table if you issue the CREATE TABLE statement according to
your DBMS' capabilities.
dbReadTable is just a shorthand for
dbGetQuery(c, "SELECT * from <table>")
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(dbObj = "JDBCConnection", obj =
"ANY", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", name =
"character", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", statement
= "character", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection", ...)
signature(conn = "JDBCConnection",
statement = "character", ...)
signature(conn = "JDBCConnection",
statement = "character", ...)
signature(conn = "JDBCConnection", ...)
A DBI driver that uses any JDBC driver to access databases.
Objects can be created by calls to JDBC or dbDriver.
identifier.quote:Quote character to use for
identifiers in automatically generated SQL statements or NA
if quoted identifiers are not supported by the back-end.
jdrv:Java object reference to an instance of the driver if the driver can be instantiated by a default constructor. This object is only used as a fall-back when the driver manager fails to find a driver.
Class "DBIDriver-class", directly.
Class "DBIObject-class", by class "DBIDriver", distance 2.
No methods defined with class "JDBCDriver" in the signature.
Methods for the class ‘JDBCDriver’ in Package ‘RJDBC’.
Most prominent method is dbConnect, it creates a new JDBC
connection using the specified driver. From RJDBC 0.2-9 on the driver
takes precedence over DriverManager, because DriverManager is static
and is not capable of finding drivers dynamically. DriverManager is
now only used if the driver is a NULL-driver, i.e., JDBC(NULL).
There are only two positional properties user='' and
password='' neither of which will be set if empty. All other
arguments are treated as additional properties passed to the
connection (except when DriverManager is used).
Additional arguments to dbConnect() properties are set
dbListConnections always return NULL with a warning,
because JDBC connections are not tracked.
dbGetInfo returns very basic information, because the JDBC
driver is not loaded until a connection is created.
dbUnloadDriver is a no-op in the current implementation,
because drivers are never removed from the JVM.
signature(drv = "JDBCDriver", ...)
signature(drv = "JDBCDriver", ...)
signature(drv = "JDBCDriver", ...)
signature(drv = "JDBCDriver", ...)
Representation of a DBI result set returned from a JDBC connection.
Objects can be created by call to dbSendQuery.
jr:Java reference to the JDBC result set
md:Java reference to the JDBC result set meta data
env:Environment holding cached objects (currently the
result helper object used by fetch())
stat:Java reference to the JDBC statement which generated this result
Class "DBIResult-class", directly.
Class "DBIObject-class", by class "DBIResult", distance 2.
No methods defined with class "JDBCResult" in the signature.
Methods for the class ‘JDBCResult’ in Package ‘RJDBC’.
fetch retrieves the content of the result set in the form of a
data frame. If n is -1 then the current implementation fetches
32k rows first and then (if not sufficient) continues with chunks of
512k rows, appending them. If the size of the result set is known in
advance, it is most efficient to set n to that size.
Additional argument block can be used to inform the driver
that pre-fetching of a certain block of records is desirable
(see setFetchSize() in JDBC) leading to possibly faster pulls
of large queries. The default is to pre-fetch 2048 records. Note
that some databases (like Oracle) don't support a fetch size of more
than 32767. If set to NA or anything less than 1 then the
fetch size is not changed. This is only a hint, drivers are free to
ignore it.
Finally, use.label logical argument determines whether
column lables are used for naming (TRUE, default) or column
names should be used (FALSE) since some database drivers do not
implement labels correctly.
dbClearResult releases the result set.
dbColumnInfo returns basic information about the columns
(fields) in the result set.
dbGetInfo returns an empty list.
dbListResults returns an empty list and warns that JDBC doesn't
track results.
signature(res = "JDBCResult", ...)
signature(res = "JDBCResult", ...)
signature(res = "JDBCResult", ...)
signature(res = "JDBCResult", ...)
signature(res = "JDBCResult", ...)