spec_arrow_get_query_arrow: spec_arrow_get_query_arrow

In DBItest: Testing DBI Backends

spec_arrow_get_query_arrow

Description

spec_arrow_get_query_arrow

Value

dbGetQueryArrow() always returns an object coercible to a data.frame, with as many rows as records were fetched and as many columns as fields in the result set, even if the result is a single value or has one or zero rows.

Failure modes

An error is raised when issuing a query over a closed or invalid connection, if the syntax of the query is invalid, or if the query is not a non-NA string. The object returned by dbGetQueryArrow() can also be passed to nanoarrow::as_nanoarrow_array_stream() to create a nanoarrow array stream object that can be used to read the result set in batches. The chunk size is implementation-specific.

Additional arguments

The following arguments are not part of the dbGetQueryArrow() generic (to improve compatibility across backends) but are part of the DBI specification:

• params (default: NULL)

• immediate (default: NULL)

They must be provided as named arguments. See the "Specification" and "Value" sections for details on their usage.

The param argument allows passing query parameters, see dbBind() for details.

Specification for the immediate argument

The immediate argument supports distinguishing between "direct" and "prepared" APIs offered by many database drivers. Passing immediate = TRUE leads to immediate execution of the query or statement, via the "direct" API (if supported by the driver). The default NULL means that the backend should choose whatever API makes the most sense for the database, and (if relevant) tries the other API if the first attempt fails. A successful second attempt should result in a message that suggests passing the correct immediate argument. Examples for possible behaviors:

1. DBI backend defaults to immediate = TRUE internally

   1. A query without parameters is passed: query is executed

   2. A query with parameters is passed:

      1. params not given: rejected immediately by the database because of a syntax error in the query, the backend tries immediate = FALSE (and gives a message)

      2. params given: query is executed using immediate = FALSE

2. DBI backend defaults to immediate = FALSE internally

   1. A query without parameters is passed:

      1. simple query: query is executed

      2. "special" query (such as setting a config options): fails, the backend tries immediate = TRUE (and gives a message)

   2. A query with parameters is passed:

      1. params not given: waiting for parameters via dbBind()

      2. params given: query is executed

See Also

Other Arrow specifications: spec_arrow_append_table_arrow, spec_arrow_create_table_arrow, spec_arrow_fetch_arrow, spec_arrow_fetch_arrow_chunk, spec_arrow_read_table_arrow, spec_arrow_send_query_arrow, spec_arrow_write_table_arrow, spec_result_clear_result

DBItest documentation built on June 22, 2024, 11:55 a.m.