5 Utilities

The bindings described in this section are provided by the specific modules below, not by db or db/base.

5.1 Datetime Type Utilities

5.2 Geometric Types

The following structures and functions deal with geometric values based on the OpenGIS (ISO 19125) model.

Note: Geometric columns defined using the PostGIS extension to PostgreSQL are not directly supported. Instead, data should be exchanged in the Well-Known Binary format; conversion of the following structures to and from WKB format is supported by the wkb->geometry and geometry->wkb functions.

5.3 PostgreSQL-specific Types

The lb and ub fields must have the same type; the permissible types are exact integers, real numbers, and sql-timestamps. Either or both bounds may also be #f, which indicates the range is unbounded on that end.

The digits themselves are case-insensitive, accepting both uppercase and lowercase characters. Otherwise, if v is not a string matching the above pattern, this function returns #f.

Added in version 1.1 of package db-lib.
Changed in version 1.8: Made the check stricter: no characters are allowed before or after the UUID.

Note: PostgreSQL’s built-in geometric types are distinct from those provided by the PostGIS extension library (see Geometric Types).

The typeid refers to the OID of a row in the server’s pg_type system table. The typename symbol is the name this library uses for the type in parameter descriptions, error messages, etc; it is not necessarily the same as the server’s type name for typeid. The server’s type name must be used in SQL statements.

When the type identified by typeid appears in a query result, the result value is first received according to basetype, then the resulting Racket value is converted using recv-convert. If basetype is #f (the default), it is treated like the bytea type; that is, recv-convert gets the byte string sent by the server. If recv-convert is #f, the type is not allowed as a result type.

When the type identified by typeid is used as a query parameter, the argument value is first converted using send-convert, and the converted value is sent according to basetype. If send-convert is #f, the type is not allowed as a parameter type.

Added in version 1.8 of package db-lib.

Added in version 1.8 of package db-lib.

5.4 Cassandra-Specific Functionality

The default consistency level is 'one.

5.5 Testing Database Programs

This module provides utilities for testing programs that use database connections.

Use this function in performance testing to roughly simulate environments with high-latency communication with a database back end.

If sleep-atomic? is true, then the proxy enters atomic mode before sleeping, to better simulate the effect of a long-running FFI call (see FFI-Based Connections and Concurrency). Even so, it may not accurately simulate an ODBC connection that internally uses cursors to fetch data on demand, as each fetch would introduce additional latency.

5.6 Unsafe SQLite3 Extensions

The procedures documented in this section are unsafe.

In the functions below, the connection argument must be a SQLite connection; otherwise, an exception is raised.

• init-acc is the initial accumulator value.

• step-func receives arity+1 arguments: the current accumulator value, followed by the arguments of the current “step”; the function’s result becomes the accumulator value for the next step. The step arguments are SQLite values; the accumulator argument and result can be arbitrary Racket values.

• final-func receives one argument: the final accumulator value; the function produces the result of the aggregate function, which must be a SQLite value.

The following relationship roughly holds:

(begin (sqlite3-create-aggregate c "agg" 1 init-acc step-func final-func)

(query-value c "select agg(expr) from table"))

= (final-func

(for/fold ([accum init-acc])

([v (in-query c "select expr from table")])

(step-func accum v)))