backend_db {dplyr} | R Documentation |
These generics execute actions on the database. Most generics have a method
for DBIConnection
which typically just call the standard DBI S4
method.
db_list_tables(con) db_has_table(con, table) db_data_type(con, fields) db_save_query(con, sql, name, temporary = TRUE, ...) db_begin(con, ...) db_commit(con, ...) db_rollback(con, ...) db_create_table(con, table, types, temporary = FALSE, ...) db_insert_into(con, table, values, ...) db_create_indexes(con, table, indexes = NULL, unique = FALSE, ...) db_create_index(con, table, columns, name = NULL, unique = FALSE, ...) db_drop_table(con, table, force = FALSE, ...) db_analyze(con, table, ...) db_explain(con, sql, ...) db_query_fields(con, sql, ...) db_query_rows(con, sql, ...)
con |
A database connection. |
table |
A string, the table name. |
fields |
A list of fields, as in a data frame. |
Note, a few backend methods do not call the standard DBI S4 methods including
db_data_type
: Calls DBI's dbDataType
for every field
(e.g. data frame column) and returns a vector of corresponding SQL data
types
db_save_query
: Builds and executes CREATE [TEMPORARY]
TABLE <table> ...
SQL command.
db_create_table
: Builds and executes CREATE [TEMPORARY]
TABLE <table> ...
SQL command.
db_create_index
: Builds and executes CREATE INDEX <name>
ON <table>
SQL command.
db_drop_table
: Builds and executes DROP TABLE [IF EXISTS]
<table>
SQL command.
db_analyze
: Builds and executes ANALYZE <table>
SQL
command.
db_insert_into
and db_explain
: do not have methods
calling corresponding DBI methods. The latter because no underlying DBI S4
method exists and the former because calls to the corresponding DBI S4
method (dbWriteTable
) need to be able to specify an appropriate
combination of values for non-standard append
and overwrite
arguments.
Currently, copy_to
is the only user of db_begin()
, db_commit()
,
db_rollback()
, db_create_table()
, db_insert_into()
,
db_create_indexes()
, db_drop_table()
and
db_analyze()
. If you find yourself overriding many of these
functions it may suggest that you should just override copy_to
instead.
Usually a logical value indicating success. Most failures should generate
an error. However, db_has_table()
should return NA
if
temporary tables cannot be listed with dbListTables
(due to backend
API limitations for example). As a result, you methods will rely on the
backend to throw an error if a table exists when it shouldn't.