7 Quick find procedures

(require (planet untyped/snooze/quick-find))

Quick find procedures provide convenient shorthands for retrieving persistent structs based on the values of their attributes. The procedures can be defined on a per-entity basis using the constructor macros custom-find-one, custom-find-all, custon-find-count and custom-g:find.

The constructor macros are described below and the quick find procedures themselves at the bottom of the page.

(custom-find-one entity kw-arg ...)

kw-arg   =   #:order (order-clause ...)

Defines a quick find wrapper for find-one. entity is the struct type identifier for an entity (e.g. student) and the order-clauses are as they appear in the syntax query language (see sql).

(custom-find-all entity kw-arg ...)

kw-arg   =   #:order (order-clause ...)

Like custom-find-one but defines a wrapper for find-all.

(custom-g:find entity kw-arg ...)

kw-arg   =   #:order (order-clause ...)

Like custom-find-one but defines a wrapper for g:find.

(custom-find-count entity kw-arg ...)

kw-arg   =   #:order (order-clause ...)

Like custom-find-one but defines a wrapper that finds the count of the matching structures in the database.

The quick-find procedures produced are keyword procedures that accept keywords with the same names as the attributes of the relevant entity. For example, the find-person procedure below:

(define-persistent-struct person

([name        type:string]

[age         type:integer]

[programmer? type:boolean]))

(define find-person

(custom-find-one person #:order ((asc person.name))))

would accept keyword arguments for #:name, #:age and #:programmer?. These attribute arguments can be used in the following ways:

• Passing a boolean, numeric, string, symbol, time-tai or time-utc literal matches structs with a specific attribute value.

• Passing a list of literals matches structs with any corresponding attribute value.

• Passing #f for any non-boolean attribute matches structs with null attributes.

• Passing void matches any value at all (useful when wrapping quick-find calls in other procedures).

• Arbitrary expressions may be specified by passing a procedure of type (attribute-alias -> expression).

Quick find procedures also accept #:what, #:order, #:limit and #:offset arguments:

• the #:what argument accepts an entity, attribute, expression, or list of attributes or expression;

• the #:order argument accepts a list of order terms;

• the #:limit and #:offset arguments accept a natural number or #f.

Examples:

; SELECT * FROM person WHERE name = 'Dave';

(find-person #:name "Dave")

; SELECT * FROM person WHERE name = 'Dave' AND age = 30;

(find-person #:name "Dave" #:age 30)

; SELECT * FROM person WHERE name IN ('Dave', 'Noel', 'Matt');

(find-person #:name (list "Dave" "Noel" "Matt"))

; SELECT * FROM person WHERE name IS NULL AND "programmer?" = false;

(find-person #:name #f #:programmer? #f)

; SELECT * FROM person;

(find-person #:name (void))

; SELECT * FROM person WHERE name ~ 'D.*';

(find-person #:name (lambda (attr) (sql:regexp-match attr "D.*")))

; SELECT surname FROM person;

(find-person #:what (sql person.surname))

; SELECT * FROM person ORDER BY surname DESC;

(find-person #:order (list (sql (desc person.surname))))