source: trunk/third/oaf/docs/query-language.txt @ 15904

This file documents the Grand OAF Database Query Language.

        Constants:

Strings: As in SQL, delimited by single quotes. Example: 'mystring'

Stringvs (string arrays): A comma-separated list of strings, surrounded by square brackets. Example: ['red','blue']

Numbers: Floating point decimals. (aka "whatever atof() accepts" :)

Booleans: TRUE or FALSE (other common boolean value identifiers also accepted, but not encouraged).

        Field identifiers:

Names of fields are attributes of a ServerInfo record. These include
'type', 'location_info', and 'iid', even though these are explicitly
stored instead of just other attributes.

Some pseudo-fields are also available - they are all prefaced with an underscore:
        _active - Whether the server is currently running (boolean)

        Variables:

Variables are various miscellaneous data items that are part of the
environment. The syntax for referring to a variable is a '$' sign
followed by the variable name. The following variables are available:

$hostname - the hostname that the requesting client is running on.
$domain - the "domain" that the client is requesting activation in.

        Functions:

Functions perform transformations on data and return a result. There are two possible syntaxes for a function call:
        funcname(arguments)
        field.funcname(other-arguments...)

Internally, 'field.funcname(other-arguments...)' is translated to be
exactly the same as 'funcname(field, other-arguments)', so
'priority.max()' is exactly the same as 'max(priority)'. The following functions are available:

defined(expression)
   Returns a boolean value that indicates whether the given expression is defined for the current
   record. For example, using a field name would indicate whether that field is defined for the
   record.

has_one(stringv1, stringv2)
   Returns a boolean value that indicates whether any of the strings
   in the 'stringv2' array are contained in the 'stringv1' array.

has_all(stringv1, stringv2)
   Returns a boolean value that indicates whether all of the strings
   in the 'stringv2' array are contained in the 'stringv1' array.

has(stringv, string)
   Returns a boolean value that indicates whether 'string' is contained in the 'stringv' array.

prefer_by_list_order(string, stringv) 
   This function is intended to use as a sort condition when you have a prioritized list of 
   preferred values. It returns -1 if the 'string' is not in the 'stringv' array, otherwise 
   it's position measured from the end of 'stringv'. The result is that the first item is 
   most preferred, items after that are next most preferred, and items not in the list are 
   lowest priority.

max(expr)
   Evaluates 'expr' over all the available server information records in the database, and returns
   the maximum value as dictated by the normal sort order for the data type of 'expr'.
   This function is not valid for string vectors.

min(expr)
   As with the 'max' function, but finds the minimum value.

Function names are case insensitive.

        Operators:

Binary relational operators 

==    equal
!=    not equal
<     less than
>     greater than
<=    less than or equal
>=    greater than or equal

Binary boolean operators

&&, AND   and
||, OR    or
^^, XOR   exclusive or

Unary boolean operators

~, NOT    not

Binary arithmetic operators

/   divided by
+   plus
-   minus
*   times

Unary arithmetic operators

-   negate


        Example queries:

To get a component implementing the IDL:GNOME/Graph/Layout interface you might use:

CORBA_Object o = oaf_activate ("repo_ids.has ('IDL:GNOME/Graph/Layout:1.0')",
                               NULL, 0, NULL, &ev);

A more complicated query might be:

"(repo_ids.has_all (['IDL:Bonobo/Control:1.0',
                     'IDL:Nautilus/ContentView:1.0']) OR
  repo_ids.has_one (['IDL:Bonobo/Control:1.0',
                     'IDL:Bonobo/Embeddable:1.0'])) AND
  repo_ids.has('IDL:Bonobo/PersistFile:1.0') AND
  foo:bar.defined()"

This would get any component with both 'Control' and 'ContentView' or
with either 'Control' or 'Embeddable' as long as they supported the
'PersistFile' interface, and defined the attribute 'foo:bar'.